Instruction/ maintenance manual of the product 494A Tektronix
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Service Manual 494A & 494AP Tektronix o o o o o o o o o o o I o o o o a o o o o o o o o o o o o o o a o o a o o o o o o o o o Spectrum Analyzers Volume 1 070-ss60-00 Warning The servicing instructions are for use by qualified personnel only. To avoid personal injury, do not perform any servicing unless you are qualified to do so.
Copyright @ Tekrronix, Inc. 1987. All rights reserved. Tektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supercedes that in all previously published material. Specifications and price change privileges reserved.
o o o o o o o o o o a o I o o O o o o o o o o o o o o O I o o o o o o t o o o o I O a o RELEASE OF COPYRIGHT Tektronix cannot provide manuals for measurement products that are no longer eligible for long term support.
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I o o I o I t I o o I I O o I t o I I o o o o o o o t o I o o o o o I o O t I O o O t o WARRANTY Tektronix warrants that this product will be free from defects in materials and workmanship fbr a period of one (l) year from the date of shipment.
O a o I ? o a a a a a I t o I a a a O o O o o o t C a I a o O t a o a o a o o a o o I o.
o o o t o o I I o a O I a o I I o t I o a o O o I o o o I o o I o o o a o I a o o o o o PREFACE This manual contains servic€ information for the TEKTRONfX 494A1494Ap. The information is tocated in two volumes. Volume 1 contains the text and Volume 2 contains the diagrams and parts lists.
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TABLE OF CONTENTS The 494A/494AP service Manuat is divided into two volumes. VOLUME 1 Page PREFACE ........................ i TABLE OF CONTENTS .............. .......... iii LIST OF ILLUSTRATTONS ........... ........ x LIST OF TABLES ............. xiii SERVICING SAFETY SUMMARY .
o o o I .| r o o a a o I o o t a o O o o o I a o o o t o a a I I I o o o o o I o a a a o tv 49441494AP Servtce Vot. i Section 4 Section 5 TABLE OF CONTENTS (Gonr.) page PERFORMANCE CHECK (Conr.) 24. Check LO Emission .....4-29 25. Check 1 dB Compression point .
TABLE OF CONTENTS (Conr.) o o o I O I I o o O I a o o a I o I o o t o o o a o o o I o a a t o O o I o o o a o o o 494A/494AP Service Vot. 1 Section 6 page MAINTENANCE (Conr) Firmware Version and Enor Message Readout ............... 6-1 5 Selected Components .
TABLE OF CONTENTS (Cont.) Page Section 7 THEORY OF OPERATTON (Cont) DETAILED DESCR|PT|ON ................ ..... 7 -4 1ST CONVERTER SECTTON ............. 7_4 RF Interface Qircuits .................... 7-4 'l st Converter ................. ........
TABLE OF CONTENTS (Conr.) o o o o o o O a o o o a o I t I o I o o I o o a o o o o o t o a I o o t t o a O o o o a 494A1494AP Service Vot. I Page Section 7 THEORY OF OPERATION (Conr) Fast Retrace Blanking ...,.,... 742 Memories ........7-47 DEFLECTION AMPLIFIERS .
TABLE OF CONTENTS (Cont.) Page Section 7 THEORY OF OPERATTON (Conr) DtctTAL CONTROL SECTTON .......... 7_88 Microcomputer ............................. 7-gg Processor ............. 7-gg Microprocessor ................... 7-88 Cfock ......... ......7-92 Microcomputer Bus .
494A/{94AP Service Vot. 1 TABLE OF CONTENTS (Cont.) VOLUME 2 Sec|ion 9 REPLACEABLE ELECTRICAL PARTS Section 10 DTAGRAMS Section 1.I REPLACEABLE MECHANICAL PARTS.
494A/494AP Servlce Vol. 1 Figure page The 494AP Spectrum Analyzer. ................... xvi 2-1 Dimensions. ....,....,..2-12 3-1 Location of input power selector switch and fine fuse. .._....... .....,..,.........9-2 4-1 Crt display at initial power-up.
LIST OF ILLUSTRATIONS (Conr.) Page Flgure I o o a o I I o o a I a t o I I o t o o I t o a o o a o I I a o o o I o I o a o o o o I 494A/494AP Servtce Vot. 1 Figure 5-21 PreseleetorDriver adjustment setup. ......... ............5_22 5-22 Preselector Driver test point and adjustment locations .
494A/494AP Servlce Vot. 1 o I o a I I o a o I I I o o O t o o o I a I o o I o o o o ) o o a o o I a o I o o o o t LIST OF ILLUSTRATIONS (Cont.) Page Figure Figure 7-12 Selection of disptay position on the log scale. .....7-94 7-13 Functional diagram showing the sp€ctrum analyzer and 1405 TV Sideband Adapter system.
o a o a o O I I O o o I o I t I I I I I o I o a I o t o I t a o o o a o I o o o o o o o 494A1494AP Service Vot. 1 Table page 1-1 TEKTRON'X WAVEGUIDE MIXERS .............. 1-3 2-1 FREQUENCY RELATED CHARACTERTSTTCS .................. 2-1 2-2 AMPLITUDE RELATED CHARACTERTSTTCS .
{944/494AP Service Vot. 1 Table page 8.1 EXTENDED SERVICE AND WARRANW OPT|ONS .............8_1 8.2 OPNON 07 ALTERNATE spEctFtcATloNs ................... 8-2 8.3 OPTIONS 21 AND 22 WAVEGUIDE MtxERS CHARACTERTSTTCS ...................... 8_3 page OPTION 41 ALTERNATE SPECTF|CAT|ONS .
t o o I o I I I o o o a o O t I o I o I I o o o o I o o o o o o I o o t a o o o o o I I SERVICING SAFETY SUMMARY FOR QUALIFIED SERVICE PERSONNEL ONLY 494A|494AP Service Vot. 1 Do Not Service Alone Do not perform internal service or adjustment of this product unless anoth€r person capable of rendering first aid and resuscitation is present.
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GENERAL INFORMATION Product Description The 494A and the 494Ap (programmabte) instru_ ments are high performance, compict, portable spec- trum analyzers. Microcomputer control of most func- tions simplifies and enhances operation. The analyzers feature: .
Generaf Infornation - 4g4[l4g4Ap Service, Vol. 1 throughout the United StatEs and in countries wherE our products are sold. Several types of maintenance or repair agreements are available. For example, for a fixed fee, a maintenance agree- ment program provides maintenance and recalibration on a regular basis.
I o o a o I I o o o o o o o a o a o t I I o o a t o t o I o o o I a o o o I o o o a I o EXAMpLE: R2090 on assembly A2O becomss 420R2090. EXAMpLE: U1044 on subassemblv Al of assembly A36 is found in the ejectrical parts tist as A3641U.
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I o a I o o o t o o o J o o o o I a t a I a o o o o o o I o I o I a o C I o o o o I I o Section 2 - 494A1494Ap Service, Vol. 1 SPECIFICATION This section includes the eiectrical, physical, and environmental characteristics of this insirument. Any instrument specification changes due to options ari listed in the Options section of this manual.
Table 2.1 (Continued) Characteristic Perf ormance Requirement Supplemental Information I nitial Accuracy (continued) Bands 1& 5-12 with SPAN/DIV (200 kHz, and Bands 2-4 with SpAN/DlV (100 kHz (1st.
Specification - 494Al4g4Ap Service, Vol. 1 - Tabte 2-1 (Continued) FREOUENCY RELATED CHARACTERISTICS tal Inlormation Characteristic Signal Counter (continued) Delta Frequency Accuracy Sensitivity Read.
Specilication - 494A/494Ap Service, Vot. 1 Table 2-l (Continued) FREQUENCY RELATED CHARACTERTSTICS Characteristic Performance uirement Supplemental Inf ormation cally (-55 dBc (47 Hz - 44A Hz) 3 kHz 300 Hz 30 Hz 3Hz 0.
o o O a o o a t o o t o o o o o e o I o I o ? O o o e o o I o o o o o o o o a o o a o o Characteristic Frequency Span/Div (cont) Multiband Mode Maximum Span/Div Band 1 (0-1.
Characteristic Performance Requirement Supplemental Inf ormation requency Response Coaxial (direct) Input Band and Freq Range 1 (10 kHz-l.8 GHz) 2 (1.7-5.
Characteristic Specification _ 494A1494Ap Service, Vot. 1 AMPLITUDE RELATED CHARAiTERISTICS tal Informalion Top of the graticule. From -117 dBm to +50 dBm; +50 dBm inctudes 20 dB of tF gain reduction (+30 dBm is the maximum safe input). Alternate reference levels arei .
Specification - 494A!494Ap Service, Vol. 1 Characteristic Reference Level (continued) SEt With DATA ENTRY buttons Vertical Display Modes Display Dynamic Range Accuracy 10 dB/div Log Mode 2 dBldiv Log Mode Linear Mode RF Attenuatol Range Accuracy Dc to 1.
o o o I o o o o o o o c I o o o o o a o I o o ) o o o o I o ? o a o O o o I o o a o I o Specification _ 494A1494Ap Service, Vot. 1 Tabte 2-2 (Continued) AMPLITUDE RELATED CHARAiTERISTICS Characteristic lF Gain Range Accuracy 'l dB Step .
Table 2-2 (Continued) Characteristic Perf grmance Requirement Supplemental Intormation Sensitivity Frequency Range Band 1 10 kHz-'t.8 GHz Equivalent Input Noise in dBm vs. Resolution Bandwidth quivalent maximum input noise rr each resolution bandwidth.
I o o t o I o I o t I o o I a I o o o o I o o o o O t e t c o o o o o o o I o o o I t 3 Characteristic RF INPUT lmpedance VSWR with 10 dB or more RF Attenuation 10 kHz-2.5 GHz 2.5-6.0 GHz 6.0-18 GHz 18-21 GHz VSWR with 0 dB RF Attenuation 10 kHz-2.5 GHz 2.
Specification - 494A1494Ap Service, Vol. 1 Characteristic HORIZITBIG (Rear Panel) Sweep Input Voltage Range Trigger Input Voltage Range Minimum Maximum dc + peak ac Pulse Width MARKERIVIDEO (Rear Pane.
Characteristic Speclfication - 494Al4g4Ap Service, Vol. 1 Table 2-3 (Continued) INPUT SIGNAL CHARACTERISTICS Supplemental Inf ormation Internal Control. High (default) selects internal control. lnstrument bus lines are output at the J104 ACCESSORy connector.
Specification - 494At494Ap Service, Vol. 1 Characteristic EXTERNAL MIXER Bias Range VERT (OUTPUT) (Rear Panet) HORIZ (OUTPUT) (Rear panet) PEN LIFT (Rear Panel) 10 MHz lF (OUTPUT) (Rear Panet) IEEE ST.
o o o o t I t o o t o o o t o o o t o o o a o o t o t o o I o o I o o o I o o o I o o I Characteristic Sweep Modes Sweep Time Accuracy Triggering Internal Trigger Level External Trigger Input Level Cr.
Speclfication - 494A1494AP Service, Vot. 1 Table 2-7 ENVIRONMENTAL CHARACTERISTICS Vibration (operating) (instrument secured to a vibra. tion platform during test) Meets MIL T-28800C, type class 3, style C specifications. Characteristic Descr Temperature Operating and Humidity -15oC to +55oC/95"/" (t 5o/" relative humidity).
o I a o , t a o o o ) I o t o I o o o J a a O o o t a o I t o o o o o o o o J o o o o , Characieristic Weight Dimensions (see Figure 2-1) Without Front Cover, Handle, or Feet With Front Cover, Feet, and Handle Handle Folded Back Over the lnstrument Handle Fully Extended Specificaiion - 494A1494Ap Service, Vol.
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a O o a o o I I o t I ) I o a I a o o a o o o o o a o o I o o O I o a a o a o o o O o o Section 3 - 494A1494Ap Service, Vot. I INSTALLATION This section describes unpacking, installation, pow€r requirements, storage information and repackag- ing for the spectrurn analy;er.
Installation - 494A/494Ap Servlce, Vol. 1 CONNECTING POWER Power Source and power Requirements o a o I a a o o O a o a o I I o o o t o a o o o o O o o o o o O o o a o o o o o o o ) a g-2 Changing the powef input can be dangerous.
o o o o o o o o o o o a o o o o o o o o o o O o a o o o o o a o O o o o o a o o o o o o Long Term - For instrument storage of more than 90 days, retain the shipping container ti iepacXage ttre instrument. The battery in tt e instrume-rit does not require rernoval.
O o o o o a o o o O o o o o o o o o o o O o o o c o O o o o a o o O O o o o I o o o o o.
PERFORMANCE CHECK Introduction All performance checks are carried out without removing the instrument covers. The procedures in this section verify that the instru- ment performance satisli€s the performance require- rnents specified under the performance Requirement column in Section 2, Specification.
Performance Check Procedure - 494A/4g4Ap Service Vol. 1 Table 4-1 EOUIPMENT REOUIRED or Test Flxture Test Oscilloscope Time Mark Generator Frequency Countera Prescaler Function or Sine-Wave Generator .
o o o o o o o o o o o o o O o a o o o o o o o o o o o o o o o o o o o o o o o o o o o o Performance check procedure - 4g4br4g4Ap service vor. 1 Table 4-1 (cont) EOUIPMENT REOUIRED Equipment or Test Fi.
Performance Check Procedure - 4g4Ll4g4Ap Servlce Vol. 1 PRELIMINARY PREPARATION o o o o a o o o o o o o o o O o o o o o o o o o o o o o o o o o o o O o o o o o o o o o 4-4 lnitial Power-Up During init.
E -28( o a. s r rotx f, -t { { { - -r - - -ta .C DII I I t' I ssqx2 o o o o o o o o o O o o o o a o o o o o o o o o o o o O o o o o o o O a O o o o o O a o Performance Check procedure - 4g4Ll4g4Ap Service Vol. 1 Figure -4-2. Typical display of catibrator signat In Max Span/Div.
Performance Check Procedure - 4g4Ll4g4Ap Servlce Vot. .l PERFORMANCE CHECK PROCEDURE 1. Check 10 MHz Reference Oscillator Accuracy (Aging rate <1 x 10-7) The 10 MHz Reference Oscillator accuracy is not a performance requirement; however, it must be checked so the center frequency accuracy can be verified.
o o o o o o a o o a o a o o o I a o o o o I o o o o o O I I o o O o I I o O O o a o o o 4. Check Center Frequency Accuracy . This is a two part procedure; part I checks center frequency accuracy with the 1st LO unlocked, part ll checks accuracy with the l st LO phase lockecl.
Performance Check procedure - 4g4A/4g4Ap Service Vol. 1 TM 5OO Main Frame Flgure 4-3. Test equipment setup for checking center f.equency accuracy. Tabte 4-2 CENTER FREOUENCY ACCURACY CHECK POINTS (1sr.
o o o o o a a I o o o o a o a O a o a a o o o o a o o o O o O o o o o a o o o o o o a o wrTlt F|RST stOilAL ATC€NTER, SEOol{D CAil EE Wrn$t TH|S RAI{OE r| _ta -tt -tl {l -€ € 4' { {l 5s6035 Figure 4-4. Cenler frequency drift with the 1st LO tocked.
Performance Check procedure - 4g4Al4g4Ap Service Vol. 1 cr gl.TttB lm{ iv ra.l ta., t2.a a.l a.a 2-a t.l A C.bubu|g tbp. of |lteon|.. E -2$el .a( t.5:rrq _2rS/--* n la.a ta.t t:.t ra. a,l a.a {.1 2.4 a.l .T IM n B. Lr.r|dog Ft .t lhc drylato||/dl'rlaloo ot urc roapo||ac.
E -Otr .rr t.Eq' i5tr TI -t -- ..4 -r -tt - { -ll ^rla trl 'l ''t I' r' ss603it o o o t O o a o o a o a O o t O a o a a O o o o a o o o a o I o o o o o t t a o o o I o Performance Check procedure - 4g4AJ4g4Ap Servlce Vol.
Perlormance Check procedure _ 4g4A/494Ap Service Vol. 1 8. Check Marker Accuracy Accuracy with the 1st LO untocked is * {(20% of the Span/Div or Resolution Bandwidth, whichever is greater) + (CF x Reference Frequency Enor) * 15N kHzl. Accuracy with 1st LO tocked is * ((20% of the Span/Div or Resolution Bandwidth, whichever is greater).
o o a o o o a o o I I t o a a o a o o o a I o O o o t o I O t a o a a O O I O o o o o o Performanee Check procedure _ 4g4Al4g4Ap Servlce Vol. 1 SPECTRIfr AI{I.AYZER UI{OER TEST coME OENERATOR MOOULE Figure 4-7' Test equipment setup for checklng frequency span/Dlv and sweep Time/Div accuracy.
Performance Check procedure - 4g4A/4g4Ap Service Vol. 1 b. Activate PULSE STRETCHER and nore that this mode extends the talt time of the markers. c. Remove the test equipment. o o o o I o ) o o o a a o a o a t o o o o o a o O o o o o a o O a o o O o o a o I o I o Figure 4€.
I o o t o t o I o o I I o a a a a O a a o o o o a o o a a I a o I o o o o I O o I o I o Perlormance Check procedure _ 4g4Ll4g4Ap Servlce Vot. 1 g. Check the resolution bandwidths and shape fac_ tors for the 100 kHz (300ftHa for Option bA, 10 kHz, 1 kHz, and 100 Hz fitters.
Performance Check procedure _ 4g4Al4g4Ap Service Vol. 1 14. Check Frequency Response (Response, about the midpoint between two €xtremes, measured with 10 dB of RF attenuation and peaking optimized in the applicabl€ bands for each center frequency setting, is as follows: Band 1: +1.
Perforrnance Check procedure _ 4g4Ll4g4Ap Servlce Vol. 1 4-17 o o o o o a o I o o a o o a a I o I o o o a o o t o J a t t O a I o a o o o o a a o I o Oscillator Sweep Range 3-5.
Performance Check procedure - 4g4A/494Ap Service Vol. 1 ^ b: Check frequency response from 10 kHz to 10 MHz (lower end of Band 1). - (1) Reconnect the_test eguipment as shown in Fig- ure 4.
t I a o o o o o o o t a o o o a o a a a o a o o a I a o o o o o o o o I t I o O a a I t Performance Check procedure _ 4g4Ll4g4Ap Servlce Vol. 1 (4) Check that amplitude deviation from the 100 MHz reference_does not,*.""J-*i.s dB. Atso check that flatn€ss is within *1.
Performance Check procedure - 494A/4g4Ap Service Vol. 1 d. Check that the signal steps down in 10 dB (r1.0 dB) steps as attenuation is added. Maximum cumulative error should not exceed 2.0 dB over the 80 dB range. e. Deactivate the NARROW VTDEO F|LTER, return the external attenuation to 0 dB, and change the VERTI- CAL OISPLAY to 2 dB/DlV.
t o a o I o o I a a o o a O I I I a O o o o o o a O a o I I o O O o t o o o o I o o a I Cal Factor Test frequency Mode dBm Range Hotd Out .h. setthe signat gen€rator (Hp g3508/s3595A) con- trols as follows: Performance Check procedure - 4g4Al4g4Ap Servlce Vol.
Performance Check procedure _ 4g4Ll4g4Ap Servlce Vol. 1 o o a o o o O o o a o I o o o I o I o o ) I o o I o a o a I I a a o t t a a o a a a o o o. Check that the difference between the SAVE A and V|EW B_disptays is tess than O.S dB up to 1.g GHz, less than 1.
o I ) o o o o o a I o o I o t I t a I o o o o o I O o o o I o o t o a t I I a o o t I o Performance Check procedure - 4g4Al4g4Ap Servlce Vol. 1 b. Connect the test eguipment as shown in Figure 4-15.
Performance Check procedure - 4g4Al4g4Ap Service Vot. 1 f. Turn off the 50 MHz reference on the power rneter, and disconnect th€ power sensor from the Power Ref Output port. - g. Collect the generator output to the Spectrum Analyzer RF lN through the precision cabte and 10 dB attenuator.
o I a o o o o o o a o I o o I I , o I o I a o o a a a o a o O a I o o t I t o o O a I o .. q: 19.gt the Spectrum Analyzer RF attenuator set- ting to 60 dB, and increase the reference level setting by t0 dB. .r, lheck that t,€ {itEreqce between the SAVE A and.
Performance Check procedure - 4g4Al4g4Ap Service Vol. 1 19. Check Gain Variation Between Resolution Bandwidths (Less than *0.4 dB with respect to the 3 MHz fitter and less than 0.
o o I o o o o o o a o o o o o o I o I I O a O o o o o o o o a a I o o a I o I a o o o a Performance Check procedurc - 4g4Ll4g4Ap Service Vol. l Table 4-8 SENSITIVITY. tN dBm (dBmV for 75o tNpUT) 21. Gheck Residual Spurious Response With no input signat, -100 dBm oi tessl _a.
Performance Check procedure - 4g4A/4g4Ap Service Vol. 1 Spactum Analtrar Un(br Totl al|C T{oilt clot Figure 4'16. Test equlpment setup for checking intermoduration distortion. o o t o a o O a o I o I o a o I I a o t o o o o o o o o o o t o o o t I C a a O o o o o freq.
o o o o I o s o ) o o o o o I I I t I I I a o o o o o o o t a I a o o a I I o a t a I a 23. Check Harmonic Distortion {-60 dBc or tess frorn 10 kHz to 1.g GHz) {Not discernible above tt " "u"r"g" no]r" ftoor (at teast 100 dBc) from 1.
Performance Check procedure - 4g4Al4g4Ap Service Vol. 1 Spectrum Analyeer Under Test Figure 4-18. Test equipment setup lor checklng harmonic distortion. d. Monitor the 10 MHz lF output on the rear panel with a test sp€ctrum analyzer through a 1 dB step attenuator.
o I o o o o o I o e I o o o a o {l I I a I o o a o o e o o I o o o o i o I I o a C o o a l. Check that the 1 dB compression point occurs at -20 dBm or less (20 dB or less attenuation Oetween the generator and the RF INPUT). 26. Check External Reference Input power (+15 dBm to -15 dBm) (1 MHz, 2 MHz, 5 MHz, or 10 MHz.
Performance Check procedure - 4g4A/4g4Ap Service Vol. l Speclnm Andyrcr Undcr Tcst Iodrl.l.d RF Figure 4'20. Test equlpment selup for checking Intemal trlgger characteri3tica. o a o o a o I a o t t e o a o o o a f o t o a o o O o o o a a o o a a o o a o a c o o a 4-32 b.
a. Connect the test eguiprn€nt as shown in Figure 4-22. Set the Spectrum enityzer "ontroi, "i fouows: VERT|CAL DTSPLAY 2 dB/DtV T|ME/D|V EXT VIEW A and V|EW B Otr b. Set the function generator controls for no output (0 v). c. Use thE POSITION "ontroi to position the crt beam -on the left graticule edge.
Performance check Procedure - 4g4Al4g4Ap servrce Vor. I 29. Check VERT OUTPUT Signal (0.5 V *5% per division of disptay from the center line) a. Monitor the VERT OUTPUT with a dc_coupted test oscilloscope. b. S€t the test oscilloscope controls for a sensitivity of 1 V/div and a sweep rate of 10 ms.
32.Gheck Option 07 Frequency Response (Response, about . tt"' rniJioini'.0!i*""n two €xtremes, measured with 10 dg oi nF-ettenuation, is *2 dB from S MHz to 1000 MH;i farts.lt-trryugh f check frequency response fro.m t0 MHz to 1 GHz, anO'partJ g il;;;; i;ff;:.
Performance Check Procedure - 4g4A/4g4Ap Servlce Vol. 1 - c. Set tle_:rlveep oscillator controls for a cw output frequency of 500 MHz and an amptitude of +20 Oe;1V at the 75O INPUT. d. lf necessary, set th€ cAL AMPL adjustment for 5 divisions on the Spectrum Analyzer display.
33. Check Option 4t Frequency Span/Div Accuracv !1t73 o.t 5 MHz/Div over the cdnter 6 divisions of the display) ., Sp:laccuracy is c_hecked at center frequency set- tings of 6 GHz and 11 GHz. a. 'Connect the test equipment as shown in Figure 4-26.
Performance Check procedure - 4g4Al4g4Ap Service Vol. 1 34. Check Option 42110 MHz OUT Level ((0 dBm for Band 1) (>.-40 dBm for Band 5) . a. Tune the Spectrum Analyzer CENTER FRE_ QUENCY to 100 MHz. b. Connect a signal generator to the RF lNpUT. Set the signal generator output frequency to i00 MHz, and output level to -30 dBm.
o I o C o t o t o o I ) t I C o a o o c o o t a o o o o o o a o a o o o c O o o a o I o 7L14 Center Frequency Freq Span/Div Hz Resolution Reference Level Display Mode Digitaf Storage TimelDiv Triggering Source Mode Video Filter 110 MHz 1 MHz 3 MHZ 0 dBm 2 dBlDiv off Manuaf Free Run Norm On Performance Check procedure - 4g4Al4g4Ap Service Vol.
Performance Check procedure - 4g4A/4g4Ap Service Vol. I Lines 9000-10000: Group Execute Trigger test. Checks that a GET message does cause the Spectrum Analyzer to abort the present sweep and re-arm the trigger, causing a sweep to start and end, sending out an End-of-Sweep SRe.
o o o o a o t t o o o o t a I I o o o o o o t I a o t o I o o o o a o a o r C o o o I o Performance check procedure - 4g4A/4g4Ap service vor. 1 5130 A1-vALrr$) 5140 tF A1>0 AND A1 <31 THEN 5180 .
Performance Check procedure - 4g4Ll4g4Ap Service Vol. 1 8060 PRINT @A1:'TlM?, 8070INPUT @41:T6 8080 tF R<>T6 THEN 8100 8090 GO TO 9000 8100 PRINT "J".. GO TO LOCAL...........GTL '* FAIL *rG, 8110 cO TO 19530 8120 REM 8130 REM 8140 REM 8150 REM 8160 REM 9OOO REM "' GROUP EXECUTE TRIGGER.
t O o I o o ? o o c o o I ) o T o t o a o o o o o e a o o o o e o o ) t o o a o o I a I perrormance check procedure - 4g4A/4g4Ap servrce vor. 1 11120 REM 11130 REM 1 I 140 REM 12OOO REM " ADDRESSED AS LISTENER, TALKER "' 1 201 0 pRtNT,.
Performance Check procedure _ 4g4Ll4g4Ap Service Vol. 1 14190 PAGE 14200 A1-16 14210 GOSUB 19000 14220PR|NT" 0 L0l0 l_1o0oo. 14230 GOSUB 19070 14240 GOSUB 19190 14250 REM 14260 REM 14270 REM 14280 REM 14290 REM 15000 REM ., nLFr oR ,EOl. swlTcH .
I o o C o a I I o e C o o a o ; o I a o o a o o o e o O t o o C o o o o o o o o a ) o o performance check procedure - 4g4Ar4g4Ap servrce vor. 1 17120 PR|NT' 0L ol_ 0LO OOO I, 17130 cosuB 19d70 1 7140 PRTNT @A1 :'REF?,, 17150INPUT @At:V$ 17160 tF v$<>"REFLVL +0.
Performance Check procedure _ 4g4Ll4g4Ap Servlce Vot. 1 19260 RETURN 19270 REM 19280 REM ". SRQ HANDLER ". 19290 T6-3 19300 cosuB 19390 19310 POLL 21,21;A1 19320 PRINT @A1:"ERR?" 1.
ADJUSTMENT fntroduction l{ the lnstrument performance is not within specified requarements for a particular characteristic, determine the cause, repair if necessary, then use the appropriate adiustment procedure to retuln the instrument operation to .
Adluctment Procedure - 4g4A/4g4Ap Servtce Vot. 1 o o o o o o o ) o o o o o o ; a o o I I o O o o t o o O o o a o ) o o o t o I o a a a o Table 5-l EOUIPMENT REOUIRED Equlpment or Test Flxture lsolatio.
o o o o o o o o o o o a o o o o o O o o o o o o o o , o o o a o o o a o O o o o o o o o 1. !{iust Low Vottage power Suppty (R6028 and R6061 on the power Su'pljly board) This high-efficiency power supply uses an internal oscillator with a frequency of 66 i<fiz.
o o o o o o o o o o o o o o o o o o o o o O O o o o o o o o o O o o o o o o o o o O o o Adjustment Procedure - 494A/494Ap Service Vol. 1 F1035 F1033 R6028 {+15 V adjurt} is acceccibte throogfr screw hole Rfl)6l TP6O53 €tr8 Figure 5-1- Low voltage power supply adiustments.
o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 2. ^qlult Z-Axis and High Votrage Circuits {110?1, R1027, Rlogo,-R1ost, tno-ili0s8 on the Z-Axis board; R2O4A and R3030 on the High Vottage board) a.
AdJustmant Procedure - 494A/4g4Ap Service Vot. .l Figure 5-3. Adiustment and test point locations on Hlgh Voltage module. (3) Switch POWER back on. After the instrument initializes, activate 2 dB/Dtv and switch Digital Storage off. (4) Adjust Intensity Limit R1027 (Figure 5-2) for a voltage reading of 0.
o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o O o o o o o o o o o Figure 5-4. Test equlpment setup for adiusting the D€flection Amplifier. Adiustment Procedure - 4g4Al4g4Ap Service Vol. 1 p. Adjust C4061 for the best response. Figure 5-5.
Adfustment Procedure - 4g4Ll4g4Ap Servtce Vot. 1 Flgure 5€. Deflection Amptilier test points and adiuetments. o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o O o o o o o o o o o o o q. Monitor the collectors of e1095 and e20g6, on the Deflection Amplifier board, with test oscilloscope.
o o o o o o o o o o o o o o o O o o o o o o o o o o o o o o o o o o o o o o o o o o o o AdJustment Procedure - 494A1494Ap Service Vot. 1 lnput Gain,RlO3a O.rtput Of*t ouFur Garn R1033 | nrors iITAL STORAGE HORIZONTAL RIINC G.io R1OOo Figure 5-7. Digltal storage adiustment locations.
Adjustnent Procedure - 4g4A/4g4Ap Servtce Vot. 1 Figure 5-9. Sweep board tlming adiustment and test point locations. o o o a o O o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o The Spectrum Analyzer has a procedure in firmware for calibrating the frequency control system.
a o o o a o o o o O a o o a o o O o o o o o o o o o o o o o o o o o O o o o o o a o o '' 7. Adjust Log Amptitier (R1012, R102S, R1030, R1037, and R.t060 on the Log Amptifier board) Use only an insulated screwdriver or tuning tool to make these adjustments.
o o o I a o o o o o a o o o o o o o o o o o o o O o a o o o o o o o o o O o o o a o o (?, 5565-19 Analyzer Under Tesl &21 Ampl Bd BilC fo Sorlos:tro Ad.gtCr 'lO dB Stcp Attcnu.tor 1 dB Stcp An nu.to. m LHr Lcvclod Signrl Gcocr.to?,0-lO dBm To on Log Spectrum @"o.
o o O o I I o I o o o t o o o o o I o o o o o o o o o o a o o o o o o o a o o o a o o O .- .k. lctlvate 2 dB/Dtv and add 10 dB of artenuation. lf..the 1098 step (S division) is short, adjust the gain slightly with R'|037 in the same direction;'then rem-ove the 10 dB of external attenuation and adjust R1012 for a full.
Adjustment Procedure - 494[l4g4Ap Service Vot. 1 Figurc 5-14. Test equipment 3etup tor adiusting tlre Varlable Re3olution rnoOut". 5[ton'"*' ffi I Filrc. sotocr I 6097-18 , o o a o o o a o o a o o o o o o o o o o o o o o o o o I O o o o o O o a o O o o o o a v.
o o o o o o t t o I o O o O o o o a o o o o o a a o O o o a o O o O o o O o a o o o o o Flgure 5'15. Adiu3tmonts on the rear of tre Variabre Resorudon modure.
Adlustnent Procedure - 494ful4g4Ap Servtce Vot. 1 Flgure 5-16. 100 kHz over l0 kHz litter respona€. (1) Set the, foltowing adjustments to midrange: R4025 on the VR 2nd Fitter Select board, and R3OIO 'and R3025 in the 10Hz/100H2 Bandpass Fitter assembly.
o o o a O o o I O o I a o a o I o I O o o a o o o o a o t I o O O o o o o t a o o o o o (29) Press RECALL SETTTNGS 2. !30) Adjust C4060. in the 10 Hzl100 Hz Bandpass Filter assembly for best symmetry. lgtt Repeat parts 2g through 31 to etiminate interaction.
o O o og o o $o o3 $o oE EooE a $o go0F go o o , oH o o o Adiustment Procedure - 494A1494Ap Service Vol. 1 Figure 5-18. Adiustments on the 10 Hzl100 Hz Bandpass Filter assembly. FILTER Filter Locatlon Preset the Variable Resolution Gain and Band Leveling (R1030 on the Post VR Amplifier board) (R2031 on the Va #2 Mother board).
b, - O O o I o I o I o I O o o I o t o o o o o o o o o o I O a a o o o o I o o o o o o o Adjurtment Procedure - 494A1494Ap SeMce Vot. I e. Disconnect p693 (Figure 5-17) and activate MtN NOISE.
Adiustment Procedure - 494A/4g4Ap Service Vot. 1 10. Adjusf Calibrator Output Level (R1041 on the 100 MHz Osc and 3rd Converter board) The calibrator output level is matched to a known reference. A power meter is used to verify the output level of the reference sig_ nal generator.
o o o a o o O I o a I a a o t t t I o o O o o o o o a o I o o o I o o o o I I o o t I a Adjustment procedure - 4g4Al4g4Ap seMce vot. 1 Figure 5-20- lF gain test setup, and adjustnent and conn€ctor rocason3- 12.
Adlustment Procedure - 494A/494Ap Servlce Vot. 1 Figure 5-21. Preselector Driver adiustment lietup. o a o o o o o I o o I a a a I o o ) o a o o a O o o o o t o o a O O O o o o o o I o o o b. Set th€ test equipment as follows: Time Mark Generator .l 0 ns Comb Generator On c.
o I o o O O o I o O o I a a o o t a a o o o o o a o a O I o a o I a o o I t o o a I a a o { A Adrustment Procedure - 4g4A/494Ap Service Vol. l $tsr. h - 1,",1 ';'i 1'[ -''l Figurc 5-22. Preselector Driver test point and adiustment locations.
Adfustrnent Procedure - 4g4A/4g4Ap Servtce Vol. 1 o I o a o o o t o a I t O O o o a t o a a o a O a o o o O o a o t o o o I o o o o o o o Figure 5-23. Test equipment setup for band leveling adiustmenl 1tt.
a I o o o o o I o o o t o t o I I I o a a o o o o o t o o O a o o a o o I t o o a o o o . f. Adjust Band 2 Gain RgOg4 on th€ vR Mother b.oard #2 (Figure 5-241 tor a fult screEn (_20 OBml display.
AdJustnent Procedure - 494A/4g4Ap Servtce Vot. I To: Vsrt liignel Out (back penell Spectnrm Analyrer Under Tegt Flgure 5-25. Test equlpm€nt retup for adjusting llre phase Lock assembly.
0@ coitrnou.ED OSCIIIATOR PSI B o c1013 c,rll @@r o*tto @ (E J-ffi] @ @ snrnasrzen @ l-r rP2C3 E rpzoro El TP10'|O @ Cf 0 put.l El Ptilt- L-J @ oFFsE nrxEn @ A Syntfredror, Oftrrt l|h.r, rnd Gontlotocl Orcileor. LOOPOA0T R30!2 n TP36T E TP,OI5 EI | "trrl c2105 o fTr.
Adiustment Procedure - 494A/tg4Ap Service Vol. 1 (3) Connect the counter to Tp2o11 on th€ con- trolled Oscillator board (Figure 5-26a) and atter- nately press AUTO RESOLN and IDENT and check for a count reading of either 25.0g4g MHz or 25.0328 MHz. f.
o o o o o I o a O I a a o t o I I I I o a t a O t o o o t a o a I a o a I a o o o o o I 07) Move p2035 back to pins 1 and 2, reptace P3057, and disconnect the iest oscilloscope from the Error Amplifier board. (18) Reduce SPAN/D|V to 200 kHz and ensure that phase lock occurs, by the absence of error rnessage and a sweep.
DC503A I [[ ORF oo lc ba 1* RF OurO LO lst LO Input rrn I e RF ln I O lrtlO O P1024 P1012 P1010 (rF ouT) (OUr) (tN) H:N Adrustment Procedure - 4g4A/4g4Ap Servlce Vot, I o o o o o t I t O t o a t t o a o o o o I t a a I o o o a O a a o a o a o o o o o o o o Figure 5-27.
a o o o a t o o o o I t o I o I a o I t o a o o o O o o a o o O t a o o O O I O o o I I Sectfon 6 - 494A/494Ap Servicc Vot. 1 4. Nothing capabl€ of generating or hotding a static charge should be allowed on the work station sur- face. 5.. Keep the cornponent leads shortEd together whenever possible.
PREVENTIVE MAINTENANCE Preventive maintenance consists of cleaning, visual inspection, performance check, and if needed a recali- bration. The preventive maintenance schedule that is established for the instrument should be based on the environment in which the instrument is operated and the amount of use.
o a a o o I o o o a o ) t o t o I a t a o e a a t o t o o o t o o o I o I o o o o o I o Maintenance - 494A1494Ap Service Vol. 1 Table 6-2 SERVICE KITS AND TOOLS Nomenclature Service Kit consisting of:.
Malntenance - tl94A/494Ap SeMce Vot. 1 Schematic diagrams list the Tektronix part No. (670-xxxx-) for the assembty or board atong with the assembly number (e.9. AS0) and name. The tast two digits or sufftx of the part number are not indicated on the diagram, however, they are list€d in the El€ctrical Parts section.
Diagnostic Firmware The firmware in the sp€ctrum analyzer provldes diagnostic routines that can be used wittr itre Diagnostic part of this section to troubl€shoot th€ Frequency Con- trol system and diagnose power Supply problems. This part fottows GenErat trouOtestrbttini information.
Malntenance - 4tt0[l4g4Ap Servlce Vol. I Because the frequency control loop may be unlocked when using the internal reference freguency in a ucold' instrument.
o o o o o o o o o o o a o o o o o o a o o o o I o o o o o I o o o a o I a o | o o a o o (1) Press <Btue-SHtFT> PULSE STRETCHEB and #0, then setect either the lst to reaoout lmenu item #1) or the lnd fg.readout (menu iteni *e1. I!9 _LO frequency wiil be displayect on the crt CENTER FREQUENCY readout pbsition.
Malntenance - 494A/494Ap Servlce Vol. 1 f. lf the fuse does not open and the vottage is still absent, it indicates the trouble is the power Supply. (E) g. lf the voltage from a current limited supply is absent or low, the problem could be the supply, or cir- cuits the supply furnishes may be drawing excessive curr€nt.
Mafntenance - 4g4ful4g4Ap Servtce Vot. 1 1ST LO CONTROL DIAGNOSTIC AID NOMINAL -6.79 V 3.43 V DESIRED 2.720 504 c|-1.z 45.896 MHZ DAC TUNE VOLTS SENSE VOLTS lST LO FREQ MIXER FREO 1ST LO SETNNG ACCURACY AUXILIARY SYNTHESIZER PRESS 'SH|FT" TO EXIT -6.
Mafntenance - 494A1494Ap Servtce Vot. 1 a. lf the calculated and measured frequencies are within 50 MHz of each other and the mbasured fre_ quency agrees with the internally count€d 1st LO Freg readout or differs from it by a multiple of the Auxiliary Synthesizer Freq, r€turn to normal opera_ tion- (by pressing <Btue-SHtFT>).
(b) lf the -e1o-r-9cnr: with frequency spans greater than 5 MHz/div, ttre t si t-O is iroO- abty defective. (E) (4) lf the measured and calculated currents are not equal, th€ problem is likely in the final stage of the LO Driver. (E) 4. Measure the lst LO tuning voltage at edge con- nector 47, of the Center Frequeniy Conirot boarO.
Malntenance - 494A1494Ap Servtce Vol. 1 5. Measure the 2nd LO Tune Volts at Tp1044 on the Center Frequency Control board. a. lf the 2nd LO tuning vottage is within 200 mV of the DAC SEt value, measure the 2nd LO frequency at the front-panet 2ND LO Output connector.
a o I o ) o t o o I o ) a o o |, a o t o a o o I t o I o o o a a I o o O o e o o a o e I a. lf.b€at notes are present, press HELP to enable the lock. Check the- Error' Amplifiei output at T?2O3T, on th€ Error Amplifier OolrJln the prrase Lock module.
Malntenance - 4S4Al4g4Ap Servtce Vol. 1 o a o o a a I o o t o t a o o o t o t o o o o a o a t o o o a a a o o o o I t o o I o a TRACE MODES Trace Mode provides information on how the fre- quency control system is working. lt is acc€ssed by pressing <Blue-SHtFT> PULSE STRETCHER.
CORRECTIVE MAINTENANCE o o o o o o I o o o ) ) I t o t I o C o t o o o t o o o o o o o t o a o o C o o J o I o Maintenance - 494Al4g4fup Service Vof. 1 Corrective maintenance consists of component replacement and instrument repair.
Malntenance - 494A1494Ap Service Vot. 1 o o o o o o ) o o o o I o t I a a o o o f o a a t o o o ) o I o a o o o o I o o t a t o Table 6-4 SELECTED COMPONENTS t Number 422A1Rl070 422A1R2049 422A1R2070 .
o o 3 o o o o o o o o ) I I o I a I o o I o o o o o o o o o a o o o o o o t o o a a o o Mafntenance - 494[l4g4Ap Servtce Vot. 1 SERvIcING TooLs FoR BoARD'Tffi3.
ct66.t-14 Figure 6-2. Diode polartty marklngs. Maintenance - 494A/494Ap Servtce Vot. 1 Diode Color Code The cathode of each glass encased diode is indi- gated by a stripe, a series of stripes, or a dot. Some diodes have a diode symbol printed on one side.
o a a o o o o o o o o a o o o t O I o o e a o o o c o o I o o a o o a o a o o O o O o o lf you desire to remove the component l€ads, use a J.5 Y ol tess pencil type iron. Straigtrten-the teads on me oacK side of the board; then when the sotder melts, gently puil the sotdered tead through the hote.
o a o o a o o o o o o o o c o o o o o o ) o o o o c o o o o a O o o o I o o o o O o o o A30-POWER St,PPLY A30A57-GPIB INTERFACE A62-LOG & VIOEO ATPL A61_DIGITAL STORAGE YERT A6O-DIGITAL STORAGE }I.
O o o o o o o o o o o o a o o o o o o o a O o O o o o o o a a o a o a a o o o o o o o I Maintenance - 494Al4g4Ap Service Vot. 1 FL36 FL15 A32-110 ilHr IF AMPL 413_POWER OIVIDER A23-E29 trtHz 2ND CO}IV.
Mafntenance - 494A1494Ap Service Vot. 1 Some circuit boards and assemblies must be placed on extenders to access test points or adjustments. Before removing these boards and assembli6s, the air bafie attached to the left siderail must also be r€moved.
o o o o o o o o o o o o o o o o o o o o o o a o o o o o o o o o o o o o o o o o o o o o 5. Open the diode package. Use a pair of tweezers to grasp th€ diode assembly by its side, and place it on a static-free surface. Grasp t-he side of the'"rr"rOty with^the fingers.
Maintenance - 4g4A/4g4Ap Seruice Vot. 1 - 3. Unplug the CAL OUT coaxial cabte from the grd Converter; then disconnect the five crt cables from the Z-Axis/RF Interface, High Voltage module, and Deflection Amplifier.
o o o O a o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 7. Reinstall p361. mounting bracket then ptug pg045 onto th€ power supply board anO repacJ the cover.
Fan brackets should be installed as in Fig- ure 6-8. 7. Insert the posts of the brackets into the holes provided in the resilient mount and install the remaining bracket, with lockwashers and nuts, to the back side of the power supply housing.
o o o o o o o o o o o o o o a o o o o o o o o o o o o o o o o o o o o o o O o o o a o o Four Cavlty Fllter-The characteristics of the filter are checked with a network analyzer. Freguency of the filter is 2A72MHz, bandpass, t-S Ul-lz down, is 1 dB, return loss is 20 dB or greater, and insertion loss is 1 clB.
Mafntenance - 494A1494Ap Servtce Vot. 1 Input c1045 c2047 Flgure 6-10. 110 MHz lF test poinb and adiuetmenb. 110 MHz Three Cavity Filter Alignment of this filter is not required unless the spectrum analyzer fails to meet bandwidth specifications.
o a o o t o t o o I o a o t a O a o o o a a o o o o O o o o o o o o o o o o o o o a o o 829 MHz Converler Maintenance Some circuit boards in this assembly contain critical-length printed elements. When damaged, these elements are usually not repairable; therefore, the cir_ cuit board must be replaced.
Maintenance - 494A1494Ap Service Vot. 1 _ Check the freguency by noting the reading on the frequency counter. lf above 729.900 MHz, the stub must be lengthened. Solder a bridge across the cut "q r.e"!99 frequency. Nominal frequency for an uncut stub is 710 MHz.
o o o o o o I o o O o a O a t o a o o a O o a o a o t o a O I o I o o o o o o o o a o o g. .With the adjacent resonator (second) shorted to ground, adjust the series capacitance by benOing tne tab so the response on the_spectrum analyzer display is centered at 829 MHz (see Figure 6_16A).
Malntenance - 494A/4g4Ap Service Vol. 1 Flgure 6-'15. 829 MH: Converbr lilte. hlne tabs. Troubleshooting and Calibrating the 2nd LO The 2182 MHz Oscillator and 2200 MHz Reference Mixer contain critical printed elements that are difficult to repair.
o O o I a o o I O o o t o I o I I I o o O o a O o O a O o o a o o o O o o o o o o a o o Malntenance - 4g4A/4g4Ap service vot. 1 A 3rd Resonator Retu?n Lo-ss >12 dA B. 4th Resonator and Fllter Figure 6-17. Corect re3ponse tor g29 MHr tlrlrd and fourth resonators.
o o o a o o o o o o o o O o o o I o o o o o o o o o o o o o O o o o o o o o o o o a o o Maintenance - 494A/494Ap Servlce Vol. 1 Table 6-7 EQUIPMENT REOUIRED FOR 2nd LO CALTBRATTON Test Equipment Characteristics Recommended Type Spectrum Analyzer Frequency range to 2.
o o o a I o o I O o o O O o I o a I a a o o a o o I o O I o a O I o a a o o O o o o o o Preparing the 2nd LO Assembly lor Adjustment .. T_":! _"guipment setup is shown in Figure 6-19. Turn the POWER off. Rernove the cabinet and place the Spectrum Analyzer_upside Oown io-ine nf Oect< is exposed.
Maintenance - 494A/4g4Ap Servtce Vot. 1 2lE2 }'/Hz tro||! Unbuttcrcd OrIput Porf ffiffi o@@@ @ 9o Flgure 5-19. 2182 MHz Phase Locked 2nd LO adiustment letup.
t o a I o o o o o a o a o a o o I I o o I a a o o o I o o t a t I a I t o o o I o o t I Maintenance - 4g4Al494Ap Service Vot. 1 c2201 TP +12 V ol ?o,il,- .e: ,- zrfP2o3s-+o 5 r (2)-- r _rr r1l*rffi Figure 6'20. 16-20 MHz phase Lock circuit test point and component rocadons.
Mafnfenance - 4g4Ll494Ap Servtce Vot. 1 Figure 6-22. Coaxial test probe construction detaits. 3. Gheck the 2200 MHz Relerence Mixer a. Use a probe, consisting of a short length of semi-rigid coaxial cabte with a dc block (see Figure 6_ 22), to connect the output of the reference mixer at Q2204-to the input of the test spectrum analyzer.
6-39 o O o a O o O t o I o I o I I t o I a a o a a o o a o o I I a a I O o a o o a o a o o I Maintenance _ 494A/494Ap Service Vot. 1 Tabte 6-g EOUIPMET.IT REOUTRED FOR CALTBRATING THE 16-20]VtHz pHASE LOCK C|RCU|T Tesl fqulprng6l Characteristlcs Recommended Type utgtrat v9tlmeter Frequency Counter Time-Mark Generator Measures to within 0.
Maintenance - 494A/{g4Ap Servtce Vol. I Troubleshooting and Galibrating the 16-20 MHz Phase Lock Section Replacing oscillator components in this section may alter sweep linearity and the oscillator frequency. Thi following checks and calibration aid in repairing and retuning the assembly.
o o o a o o o o o o o o o o I o o o a a o a o o I o a a I I I a I o o a t o o o o a o o Maintenanco - 4g4A/4g4Ap Servlce Vol. 1 Figure 6-24, Tune and Sweep Range adjustnents. R404O Fine Tune Ranee -+! CENTER F REOUE'{CY COI{TROL A. Location of R4040, Fine tune Renge.
Maintenance - 494A/4g4Ap Servlce Vot. 1 5. Setting Sweep Range a. Apply 5 ps time markers from the Time Mark Generator to the RF tNpUT. Set the FREO SPAN/D|V to 500 kHz then back to 200 kHz to center the 2nd LO frequency. b. Adjust the REF LEVEL to disptay the 200 kHz markers then center one of the markers with the CENTER FREOUENCY controt.
o o o o o o o I o o o o o I I I I o a o t a o o o o o a o I I o I o o O o I a o o a o o _ ^ wIT the foop is unlocked, RF teakage from the 16-20 MHz osciilator buffer is present .ip224 with a level of --35 dBm. The-amplified Omeience frequency can be monitored at Tp20gS.
Malntenance - 4g4A/4g4Ap Servlce Vol. i 1st Converter Bias This procedure presets flatness for Band 4, Band 5, and Bands '1, 2, and 3,: then adjusts the Start (O Hzi Response amplitude and overall flatness. These adjustments should only be performed after replacem€nt of the Dual Diode Assem'bly in the First Converter.
Malntenance - 494A1494Ap Servtce Vol. 1 6-45 o o O o o o o I o o o t o o I o o o I I o o o o o o a a o o t a o a a o o o o o O a o o Table 6-9 EQUIPMENT FOR ADJUSTING FIRST CONVERTER BIAS AND START SP.
Maintenance - 4g4A/4g4Ap Servlce Vol. I Flgure 5-27. 1st LO Ddyer board adjustment and test point locatlons. o o o o o a o t o o o o o o I t o o o I o o o o o o a a o t t I o o o O o o ) o o I o o Baseline Leveling (Video processor) a. Connect the test equipment as shown in Figure 6-28.
o o a O a o o I o o I o o a t o o o o o o a o o o o o o I I a a o a I O t o o o I I o o Figurc 6-28. Baseline levefing tert setup. (6) Adjust R1069 for a triangular waveform across the screen. See Figure 6-g1b: f/) Reset Rl0tg through Rl061 to midrange.
Malntenance - 494A/494Ap Servlce Vol. 1 Figure 6-29. Typlcal basellne teveling response. o o o a o o o t o t o o o I t o o o o I a o o o o I a o o t t a o o o a o o o o o I o a (7) Activate View A, View B, and MAX HOLD. Note the response as th€ oscillator sw€eps.
Malntenance - 494A/4g4Ap Service Vot. 1 Figure 6-30. Easeline leveling adiument and test point locations. o o a o t o t o o o I a o a o o o o a o o a a o I I I o o t o a a o o I I I t a I a a I 106l (low) through R1013 (high) leyete, actiustments I t.
Maintenance - 494A/4g4Ap Servtce Vot. 1 a o a a o I I a o e o a o o o o o o a t o o o o o t a o o , t a a o o o o o t o O I o o MICROCOMPUTER SYSTEM MAINTENANCE Several maintenance aids are built into the micro- computer syst€m. Th€se operating tssts dEmonstrate correct performance or indicate the location of a prob_ lem, if any.
o I t I I I o I o t o t o o o o o a o a o a o o t a I o t t o I a o o t t 3 o o o a I t Microcomputer System Test .The microcomputer system test is chosen by setting switch #8 ctosed and switch #7 ogen in S1O6O. fni display is inoperative while this test is being performed.
Maintenance - 494A/494Ap Service Vot. 1 !. A" microcomput€r next tests U2015, a timer chip on th€ Procassor board. lf any of the timers in U201b result in timo d€lays that ar€ too short or too long, the test stops with LED DS10Sg on th€ GptB board tit.
o o o a t o t I a o o O o I o o o o I I o a o o I a o o o I o O t a a o o o I o o a o a Processor Address Decoder _ Address decoder U3035 on the processor board decodes severd chip_ sel€cts. Y0, Y'1, y5, and y7 are shown in relation to the T/6-line in Figure 6-37.
Instrument Bus Test lf the microcomputer performs the power-up self- test, but fails to properly control the instrumeht, the instrument bus interface may be faulty.
Malntenance - 4g4N494Ap Service Vol. 1 ADDR (instrument bus address) command These commands and queries are transmitted to the !ryl*rn Anatyzer with ihe pRtNT st#ment. rne upecrrum Anatyzer resp-onse to a query is input into a string variable with the tNpUT statement.
DATA (instrument bus data) query l F--{ oaraz }-.- - :^p0RjdglE*tF' 4416-08 Response to DATA query a4t$09 Combined ADDR command and DATA command Malntenance - 494Alttg4Ap Service Vol. I The address command may precede a data com- mand or query to identify the instrument bus location as part of the same m€ssage.
G. Sweep (refer to diagram 3l) The microcomputer writes to registers 0F and 1F to control sweep rate, mode. holdott, interrupts, and triggEring. H. Span Attenuator (refer to diagram 32) Registers 75 and 76 control the span attenuator. l. lst LO Driver (refer to diagram 33) Register 72 controls functions on the 1st LO Driver board.
Maintenance - 494A/494Ap Service Vot. i Table 6-13 (cont) Data Bits 76543210 Description C. Vldeo Processor (7C) 011xxxxx 001xxxxx 1l1xxxxx 010xxxxx D.
Data Blts 76549210 D. Digital Storage (cont) DB7-DBO DB7-DBO x1'lxxxxx xl0xxxxx x0lxxxxx E. Z-Axls & RF Interfaee Maintenance - 494A^l494Ap Service Vot. 1 Table &13 (cont) Table &13 {cont) Deseription Ver$cal Digltal Storage Board FA Data values from digital storage.
Table 6-13 {cont) Malntenance - 494A/4g4Ap Servlce Vol. 1 Data Bits 76549210 Descriptlon G. Sweep I o o o I o ) t o o a o o o o I o I o 3 a o o o C o o o o a o o o o o o o a a O o o t o xx00xxxx xx0lx.
o o C o I o o C o o o o o a o I O t o J a o o a o o t o t I o o o a o o o o a o o a I o x x x x x x x x x Data Bits 7654321A J. Preselector Driver (77) 0lxxxxxx l0xxxxxx 00xxxxxx xxlxxxxx K. CENTER/MKR FREQUENCY Con- trol lxxxxxxx 0xxxxxxx x0xxxxxx xx0xxxxx xxx0xxxx xxxxxx0x xxxxxxx0 DB7-DBO D87 DBO L.
Malntsnance - 494A/494Ap Servlce Vol. l Table 6-14 AUXILIARY SYNTHESTZER VALUES AS A FUNCTION OF N AND A Front-Panel Registers See Table 6-15. Table 6-15 FRONT.
I o J o I I t I o O o ) I I J t o o o o I o o o I o t o o I o o I a J ) o o o o o a a I Maintenance - 4g4ful4g4Ap Service Vol. 1 TAPE DATA TRANSFER PROGRAM Macros stored in battery-backed up memory cannot be down-loaded to tape. consequenfly, the macros will be lost each time the battery is removed from ttre f_Aemory UoarO.
Maintenance - 4g4[l4g4Ap Servlce Vot. 1 1320 T1-t1+1 1330 Next i 13a0 S1:0 1350 Print 1360 Print 1370 Print 1380 For i-1 to 10 1390 Gosub 5000 1400 lf z-0 then goto 1400 1410 Print s1;'- Settings from Data File ";t1 1424 Goto 1440 14i10 Print s1 ;"-.
o o t o I I o o o t a t a I ) I a t o a t a o o t o o o o t ) o I o ) o o o o o o a o t 237A 2380 2390 2400 2410 2420 2$A 2440 3000 3010 3020 3030 3040 3050 3060 3070 3080 3090 3100 31 10 3120 3130 3140 3150 3160 3170 3180 31 90 3200 3210 3220 3230 3240 3250 3260 3270 3280 51-sl+1 T1-tl+1 Next i Print #a1:i$ Print Print Print ".
Malntenance - 494[l4g4Ap Servtce Vot. 1 5000 ! Retrieve taped settings (s$) and send to memory tocations (s1) 5010 Z-0 5020 Delete var s$ 5030 Dim s$ to 6zt0 5040 Open #100:"FtL"&st6(t1).
o o o o t I o I o o o t o o t I o o o o o a a o t o o o o a a o o o a o a o o o o a o o 8110 Return 9000 ! This routine shows the contents of Memory disprays and settings 9010 Print "Disptay Memo.
o a o o ? o o a o o o o O o t o o o o o a o o o o a o o o o o o o o I o o a t o o a o o.
O o o o o a o o o O o a o o o t a o o a o o o o o o o a o O a o o o o a a o o O a o o o First, Second, and Third Converters Swept-frequency anatysis is achieved by a triple- conversion superheterodyne technique. Each of 'the three frequency converters consists of a rnixer, a local oscillator, and appropriate filters.
Theory of Operation - 494A/494Ap Service, Vol. 1 main lF section for processing and detection. lF Section This section processes the signal for frequency resolution. Several functions are performed here: bandwidth filtering, amplitude calibration and loga- rithmic conversion, and signal detection.
o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o Digital Control Section Operational modes and internal functions of the spectrum analyzer are selected and controlled directly from the front panel.
Theory of Operation - 4g4Ll4g4Ap Service, Vot. 1 DETAILED DESCRIPTION The following description is arranged by sections or systems; such as lst Converter, 2nd Converter, etc.
o o o o o o o o o o o o o o o O o o o o o o o a o o o o o o a o O o o o o o o o o o o o _ The 2GHz Limit€r (A10) operates from 100 kHz to 2 GHz. lt has a linear two-port transfer characteristic of unity (-1 dB) until the input exceeds +5 dBm.
Theory of Operation - 4g4A/494Ap Service, Vot. 1 Directional Filter The Directionat Fitter (FL10) couptes the 2072 MHz signal to the 2nd Converter via low-pass and band-pass filters FLl1 and FL14.
Theory of Operafon - 4g4A/494Ap Servlce, Vot. i o o o o a o o I o o O o o o o o o o o O o o o o o o o o o o o o o o O o o o o o o o o o 2ND CONVERTER SECTTON (Diagram g) Two 2nd ConvErter systgms are used in the spec_ trum analyzer. One converts 207ZMHz to 110 MHz and the other converts g2g MHz to 110 MHz.
Theory ot Operation - 494A/4g4Ap Servlce, Vot. 1 o o o O o o o o o O o a o o o a o o o o o o o o o o o o o a o o o o o o o o o o o o o o Figure 7-1. Ctpsr section of a four-cavlty filtee Selection between the two 2nd lF signals also takes place within the 829 MHz converter system.
o o o a o o o a a a o o o o a o o o a o o o o o a o O o o o o o O o o o o o o o o o o o Theory of Operaton - 4g4A/4g4Ap Service, Vol. .l Figute 7-2. Equivalent circuit of the four-cavity filter. 2072MHz RF from.the four-cavity fitter (FL14) enters the mixer, where it is switched on anO off at a 2.
Theory of Operation - 494A/494Ap Servtce, Vot. 1 Fllter to Mlxer RF Input Cable. Several products and harmonics of the local oscillator and RF input fre- quencies will exit the mixer via the RF input port of th€ mixer. The image (RF input minus the 2nd LO) and the sum (RF input plus the 2nd LO) are two significant pro_ ducts.
a o o o o o I o o a o I a o o a o O o o I o o O I o o o o t , o a o I O o o o o o o I o amplifiers provide approximatety +10 dBm to the 2072 MHz 2nd Converter and +g dBm to the Reference Mixer. Sinc€ the two buffers are..nearly identical, only the 2nd Converter buffer is described.
Theory of Operation - 4g4ful4g4Ap Servlce, Vol. 1 afray in the feedback loop of inverting amplifier ul073A. All of the amptifier's feedback is through R1072 when the output swings to the negative limit.
o a o a O o o I a o t I o o o o a o O a o o O o a o o o o o t a I a O a o o o I o o o o divide and offset lhe output of U1031 so the tune vol- tage ranges between 0 and -12.5 V. The output of divid-er Rl0gg/R1Og4 is apptied to the varactor of the 2192 MHz microstrip oscillaior (2nd LO).
Theory of Operaton - 494A/4g4Ap Service, Vol. 1 Since the amplifiers are nearly identical, the follow- ing description applies to both amptifiers. The ac and dc signal paths are treated separat€ly. Figures 74 and 7-5 are simplified diagrams of the ac and dc signal paths.
o a o a o o O I I a a t o O a o o o t a o a O a a o o o t o O o t o o a o a o o o o o o _ The 3 dB pad helps ensure a consistent 5Oo inter- face for the 829 MHz Band-pass Filter. . T!" 450 MHz High-pass Filter btocks the tower lF signals generated within the mixer.
Theory of Opera$on - 4944/4g4Ap Servtce, Vol. I off. Negative current. supplied through Rl014, €nsures that Q1011 is turned off. Diode CRt011 protects the base of 0101 1 from excessive reverse bias. Voltage across R1017 is approximately 9.4 V when e1011 ls turned on and approximately 4.
o a o I o I t t o o I t o o o o o t o a o o o O a o o o t a o a t o a o I o a o o a o o Because the grd harmonic of 719 MHz is locked to the 2182MHz reference, the tuning range ot tne 719 MHz osciilator is onty one third oithe tuning range of the reference.
Theory of Operaton - 4g4A/4g4Ap Service, Vol. 1 to lock the difference trequency from th€ Harmonic Mixer to 25 MHz. The phase/frequency detector output is a voltage that is proportional to the phase difierence between the 25 MHz refer€nce and the lF signal from the g29 MHz Harmonic Mixer.
o o o t o o o I o O o I o o a o o a t o o o o o o o a o I o I o t o o o o I o o I o t a Theory of Operation _ 4g4Al4g4Ap Service, Vol. 1 3RD CONVERTER (Diagram 4) The 1t0MHz tF Amptifier (A32) and 3rd Converter (A34) down converts the ttO MHz ouiput signat from the 2nd Converter to 10 MHz for the VariaUie Resolution circuits.
Theory of Operaton - 494A/4gdAp Service, Vot. 1 CRl029 added for maximum attenuation. lf Rl01 5 is set higher (nearer +i 5 V), diode CR3030 is forward biased and starts to conduct. Since the 2 mA supply current is relatively constant, this subtracts from the current through CRl02g.
a o o I o I o I o o o I o o o O a a o o o O o o o o a o I o a o I a O o o o a o I a I a Calibrator u2022 and related components regulat€ a 100 MHz signat to -20dBm for the front-panet ill bUf connec_ tor. VRI 0S1 serves as an aecurate 6.2 V reference, which is divided to approximately 1.
Theory of Opera0on - 4g4[l4g4Ap Servlce, Vot. 1 Tune Amplilier .. Thg FET-input operationat amptifier (Ui034) takes the output of the phasefrequency d€tector, amplifies tJre gqgr and supplies an appropriate tune vottage to the 1O0 MHz voltage controlled oscillator.
o a o I o o I I o o a I I o I I I I t o a o o o o o o o a I e a t o o t I I o o o o o o Theory of Operation - 4g4ful4g4Ap Servlce, Vot. i Table 7-3 BANDWIDTH SELECTION Bandwidth DBO DBl DB2 3 MHz t MHz 100 kHz 10 kHz 1 kHz 100 Hz 10 Hz 1 1 0 1 0 1 0 00 11 10 10 0'l 01 11 Filters are selected by diode switching.
Theory ol Operation - 494A/494Ap Sewice, Vot. 1 time. When a filter is selected, the series diodes are biased on and the shunt diodes are biased off. The diode conditions are opposite for the filters that are not selected.
a o t a t O o I o o o I o o t o a a a o o o o O o a I o a I I a o o o I o I o o o a a I - -. The.assembly consists of four subassemblies: 1st Mix-er (A69A't), Bandpass Fitter (A69A2), 2nd Mixer (A69A9), and Local Osciilator (A69i4).
Theory of Operation - 494A/494Ap Servlce, Vol. 1 After mixing, the l0MHz output signal is fittered with a second monotithic crystat fitter (y2020). This filter is important to the system operation. Without it, a large signal at 9.75 MHz woutd be present in the wide_ band VR amplifiers that foltow.
a a o a a t I t o o o I o O t o o I t o I o o a o o o o I o O a t o o a o I a o O o a t Theory of Operatlon - 4g4Al4S4Ap Servlce, Vol. 1 Table 7-4 GAIN STEP COMBINATIONS Band Leveting Circuit (Diagram 20) - The two amplifiers, in the Variable Resolution Band Leveling circuit, conect gain variations through the front end.
Theory of Operation - 49{A/4g4Ap Service, Vol. I The output of u3038A is apptied through edge con- nector pin BB to the gain control plN diode in the Band Leveling circuit.
o a o o o t o o o o o I I o I o I o t o t o o a t a o o I o o a I o ) a o o o o o a a a .. fn9 input signat. at a nominal _14 dBm, is applied through toroid transformer T1041 to the Oaii of common-emitter amplifier el040. Gain adjustment Rl0i!0, in the emitter circuit.
Theory of Operation - 494A1494Ap Servlce, Vot. 1 Table 7-5 PROGRESSION OF GAIN REDUCTION Input Level Point 1 0.01 0.0316 0.1 0.316 Point 2 0.316 0.1 0.316 Point 3 Poinl 4 Beyond Logging Range x-10 dB 0.00316 0.01 0.316 0.1 - - 0'216 X Level X+10 dB X+20 dB x+30 dB x+40 dB 0.
o o o I a' a o I o a o I o o o a o o t , I o o I a I ) o I o a o I o t I O I a o o o o o . The 10 MHz input signal from the VR circuits drives input preamptifier e2075, in th€ tog lmftiner circuits on A62A1. - The input preamptifier ir"nsier" the S0O input signal to the high_impedance input of the first amplifier stage.
o I o o o o o o o o I a I o o I I a a a t t o I o o o o o o a o a a o a o t o o a a o o Theory of Operation - 4g{A/494Ap Servtce, Vol. 1.
I I o a a t o t o a o I o o o a I t o a I o o I o o I o t o o o I o I o o I o o a o o o Theory of Operation - 4g4ful4g4Ap Servtce, Vot. I DISPLAY SECTTON (Diagram 6) FUNCTIONAL DESCRT PTION The display section consists of the following major blocks: o Video Amplifier o Mdeo Processor .
Theory of Operaton - 494[l4g4Ap Servlce, Vol. 1 Figure 7-12. Selecdon ol display positlon on lhe log scale. Log mode amplifier U4030 tinearty amptifies the sig- nal. (fhe log conversion took place in the Log Amp cir- cuit.) At 2.2 V input, the output of amptifier U40S0 is 0 V.
back loop for U5030 is now open. Diode CR5035 turns on to prevent U5090 from slewing too far negative. ldentily Circuit This circuit provides a vertical offset on alternate lllcg: t9 help identify truE and fatse signats.
Theory of Operaton - 4g4Al4g4Ap Service, Vol. I Figure 7-13. Functonal dlagram rhowing the Spectrum Anafyzcr and 1405 TV Sldcband Ad.picr System. The product is converted twic€ more, amplifi€d, liltered, log amplified, and detected. This detectdO sig- nal is applied either directly to the video amplifiers of the crt or to digital storage.
a o I o o o o o o t o I a o o o I o a a I o o o o o I o I o o o I a ? o O o a o o o I a Video Leveling . -A^mjnor slope in frequency response, caused by the 1.
EXT VIDEO SELECT MARKER/VIDEO 15 VIDEO FILTER OUT 6, 11 INTERNAL VIDEO OATA BIT 1 RC FILTER u20158 Theory of Operation - 4g4A/4g4Ap Servtce, Vol. 1 o o I a e I f o o t t o o o o o o a o a t o o 'l o o a o o o o o a o I o o J I O o o I t Flgure 7-14.
The filter consists of resistors R2O2g, RZOZ1, R2022 and capacitors C3026 and C2016, "onn""t"O between U3062 and U2066. Tabte 7-6 lists itre tiiiei components in thE circuit for each of the six OanOwiOttrs. Data bits 2, 1: "1! 4 are apptied to switch U2O15B (pi-ns B, 16, and 9) which selects the components.
Theory of Operation - 4g4A/4g4Ap Service, Vol. 1 Graphical presentation of mathematic functions or experimental data is common. one such graph has a single Y value for each X value. An alternaie presenta_ tion of the data in this graph would be a table simply listing the x coordinate values along with a correspond- ing Y value for each X value.
n I .l "l I )"t*^.ocr-t rl 'l o) __l_, I rEmal t+t^ I cfocr( I IqECR^ron FoD Theory of Operadon - 4g4N4g4Ap Servtce, Vot.l o a . o I o I o o o o o t t o I a t o c a o ) ) O e o o o I o o o o t o o o a o o t I o Figure ?-15.
Theory of Operation - 4g4Ll4g4Ap Servlce, Vot. 1 As each new Y value is converted. it is added to the eight least significant bits of th€ numerator. Each carry from the most significant bit of this addition is counted by a 17-bit ripple counter. The contents of this counter and the 8-bit sum are cascaded to form a 25-bit grand total.
t o ) o t t I o o o o o I I a o o I o I o o o a o o I o I t o o o o o o I D o o o a t o stored in the display shift register. Then, as th€ A value is- read. it is cornpared with the B value and the larger of the two is loaded into the disptay shift regisier.
Theory of Operation - 494A1494Ap Service, Vot. 1 combination with multiptexer U2020, suppties the CON- STANT data to U2030. Muttiptexer U2A2O is, in turn, controlled by address bits 0, 1, and 2 to provide the proper constant data bit to u2030. Output Clrcults.
Theory of Operafon - 494A/4g4Ap Servlce, Vol. 1 o a a o : 3 a o o I a ) ? 3 o o o o o o o o a o o o I o t I t o I o a a a o a o o a o o A INTENSITY BUS REG INTENSITY VIEW A vtEw I B-SAVE A SAVE A 1O B.
Theory of Operation - 494A/4g4Ap Service, Vol. .l Marker lC. Marker lC U9020 performs several func_ tions on the Horizontal Digital Storage board: In conjunction with Horizontal Digitat storage tc U5020, it cr€ates the two waveform markers and the update marker.
o o o t o t t o o a : t o o o I a o 3 a o a o a t o o o o o o o I o a o o o o o a o o o the 500 digital storage sweep positions. The resulting clisplay appears as a bright dot sweeping across the crt, rising and falling with the signat.
Theory of Operation - 494A/494Ap Servlce, Vol. 1 ing sid€ ar€ through the parallel combination of resis- tors R4049 and R4048 and capacitor C4057. The series connection of resistor R4049 and variable capacitor C4057 provides high-frequency respons€ compensation.
o o o o o o o o o o a o o o o o a o a o o o o o o o o o o O o a I o a o O a o o a a ? O change in input power frequency or power supply vol- tage and notifies the microcomputer.' en etapiid time meter is also located on the board to give a indication of total instrument operating time.
Theory of Operation - 4g4[l4g4Ap Servtce, Vot. 1 Transistors Q1017 and Q1015 provide curr€nt for the trace rotation coil. Trace Rotation adjustment Rl021 sets the current so the displayed trace is aligned with the graticule.
o o o o o o o o o o o o ? o o o a o o o o o o o o o o o o o o o O o O o a o o o o o o o CR4078 and CR40Z at the input to U4ogil, protect the input against excessive voltage excursions. The high-voftage osciilator is protected -Oy enfteft RgOTg, (d ?/ and R4074 in case the +i00 V suppi should fait.
Theory of Operatlon - 4g4A/4g4Ap Service, Vol. I READOUT ON TIMING CHARACTER GENERATOR CHARACTER COUNTER INSTRUMENT BUS R/O HORIZ DEFLECTION Flgure 7-17.
o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o Theory of Operation - 4g4Ll4g4Ap Service, Vot. l Figure 7-18. Character on/of timlng. Character counters synchronize the horizontal and vertical scan with the Z-Axis signal from the character g€nerator lC to draw the character.
Theory of Operation - 494A/494Ap Service, Vot. 1 Figure 7-19. Charaeter scan. The counters are wired to torce the D/A converters to step through the character horizontally, a row at a time. At the same time, the pattern of dots is accessed under the control of the timing decoder logic, U2O39B and U2031.
1-OF-64 DECODER 54 CHARACTER ROM LINE COUNTER/ SHIFTER SHIFT REGISTER Theory of Operation - 4g4[l4g4Ap Servlce, Vol. 1 Flgure 7-20. Character generator block diagram.
Theory of Operatlon - 4g4A/494Ap Service, Vot. 1 Flgure 7-21. Character timing dlagram. o o o o o o o o o o o o o o O o o o o o o o o o o o o o o o o o O o o o o o o o o o o o lnstrument Bus Interface The microcomputer controls the crt readout and fre- quency marker dot over the instrument bus through the following ports.
o o o o o o o o o o a o o o o O o o o o o o o o o o o o O o o o o a a o o o o o o o a o U10418. Also, when th€ ON/OFF tine goes high, it €nables the |NCR gate, UlOgTC, to steer-the poiition counter onto the character RAM address inputs through fine driver U3042 and muttiptexers UI050 and U1046.
Theory of Operaton - 494A/494Ap Servicg Vot. 1 U1016A delays the marker dot to allow retrace white gating DOT INV low to set up th€ disptay. DOT tNV afiects th€ readout deflection outputs in the fottowing ways. 1. The horizontal output is connected either to ground, for a center-scr€en dot, or MAX DOT CON- TROL, for a max span pointer.
o o o o o a o o o o a O o o o O o a o o o o o o o o O o t a o O O o I o O o o o o a O o Theory of Opera$on - 494[l4g4Ap Servtce, Vol. 1 Flgwe 7-22. Frequency dot ma.ker simprified diagram with timing waveforms. ___r- r Fimvf +--i_-R/ooFF "^foT*---r I lla.
Theory of Operaton - 494A/494Ap Service, Vol. 1 The Frequency Control section performs the tuning and scan function for the preselector, l st LO, and 2nd LO. lt also provides the sweep voltage for the deflection amplifiers in the Display section so the crt display is coincident with the frequency scan and tun- ing.
o o a o o I o o o a I o o t o I o o o a o o o o o o o o I o o o a o o o O o o o a o o o The digital control circuits receive and decode the address and instructions from the microcomputer, select the . sweep rate, holdoff time, trigger sourcer sweep mode, control marker dac, and cont?it interrupts to the microcomputer.
Theory of Operation - 494A/494Ap Service, Vol. 1 Tabte 7-12 TRIGGER SELECTION MODES Trigger Mode Free run Internal Ext€rnal Line Table Z-13 SWEEP HOLDOFF SELECTION Sweep Holdoff Short Medium Long Sw.
o o a o a o o o o O o o o a a o a o I o o o o t o o a o O I o a O o o o o o o o o o o o Marker DAC The Marker DAC circuit provides a dc level corresponding to the marker sweep position. This occurs during retrace. allowing osciliators to operate long enough for the counter to get an accurate reading gJ the marker position.
Theory of Operatlon - 4g4A/4g4Ap Service, Vol. 1 Sweep Holdofr During retrac€, the sweep must b€ held off long enough for the timing capacitors in the integrator to discharge and the circuit to stabilize. To prevent flicker, the holdotf period must vary as sweep tim€ changes.
o o a o I O I a o o a o o I a I O o I a o o I a a o O O o I o o I O o a a o o o o a o o SPAN ATTENUATOR (Diagram 32) The span Attenuator selects the appropriate attenuation factor for the incoming swe€p signal, to establish the frequency span.
Theory ol Operaton - 4g4A/494Ap Service, Vot. 1 R2 Rl 1ok t, I 20k . I s1 4114122 Flgure 7-23. Simplified digital-to-analog convertGr, o o o o I a o o o o o o o o o ) a o I t o o o a o o o o I I o o o o o o o o a o o o o o Feedback for the output stage is provided by R1056, plus an internal resistor in U1042.
o O I o o o o o o a a a o o t a o I a a I o o a a o o a a a t I o a o o O o o o o o o I The 2" side of U4025 is contro[ed by data bits, DBS and DB6, on the e6 and e7lines trom deotS. The ,,2y, outputs of U4025 are applied through buffers in u4042 to select the appropriate attenuation factor for the out- put sweep.
Theory of Operafon - 494ful4g4Ap Servtce, Vot. 1 r The mixer bias circuit produces and outputs the required bias voltages for the 1st Mixer. . The programmable bias circuit provides peaking voltage for the Preselector or external mixers bias voltage based on data supplied by the microcom- puter.
a o a o I I o o O o I o o o o a a o o o t t o a a o I o a a o o I o o I a o o o a a I o the amplifier. This in turn, changes the current drive to the oscillator coil. Reference Supply - ., Preamplifier e2052 plus amptifie r lJ20S2 and emitter follower Q2051 , are the active compon€nts of th€ _1 O V I-ej9fl"":.
Theory of Operaton - 4g4A/4g4Ap Servtce, Vol. 1 o The tracking adjustment circuit, which compensates for different preselector sensitivities, compensat€s any pres€lector offset, and compensates for non- linear operation caused by magnetic saturation of the Preselector.
I o I o a o o o o o o , o o o I o o o I t o e o o O I o a a I I o a I I I o o o a I a o lF Ofiset The -10 V reference, from the oscillator driver, fur_ nishes the precise reference vo,tage for the lF offset circuit. Since the offset voltage is pioportionat to the lF mings 2.
Theory of Operation - 494A/494Ap Servlce, Vol. 1 Current Driver This stag€ consists of the output stage 0565/05052; FETs Q3061, eg077, and e2074: amplifiers U205,4 and U3054; and transistor e4097. When the Preselector is not in use, DB2 goes low and turns Q2074 ofi to reduce the coil current to zero.
I o o O a o o t o o I , o o o o a t t o I o a o o O a o a I o I o O t O I o o o o o I o lf the high-order device operated with no overatl linearity inaccuracy, the operation would now be com- plet€ and the low-order incrementing could occur. However, th€ DAC device can vary byine LSB of the correct value.
Theory of Operaton - 494[l4g4Ap Servlce, Vot. 1 Figure 7-26. Simplilied tune voltage converler. a o o o I a t o o a I I o O o o o O a t o o o a o o I o a , o a a o o o o o o o o I a o In addition to i.
I o a o a a o o o O I t o o I o o o a a t o a o a C I o I o o I I e a o I o o o o o a o .Data from U4035, the data buffer, is clocked into the registers each time a difierent tune voltage is required. U3050 feeds the lowest eight bits to thE liw-order DAC, u2055; U3070 teeds the higlgs1 eight bits of the high- order DAC, U2060.
Theory of Operalion - 4g4A/4g4Ap Service, Vol. 1 Low-order DAC U2055 tunes approximately +2.5mV at pin 1. and its gain is adjusted by R1O2S. l!e^ gain oj p-r_elmplifier U1065 is set at approximatety 10,000 by Rl056 and the 5O combination of R2O59 ana R2060.
I o a o o a o o o o o ) o o o a a I t I I o o t o o I o I o o o o e o o I o o o o a o o Theory of Operation - 4g4ful4g4Ap Service, Vot. 1 100 MHz reference signal from th€ grd Converter, is divided down to 25 MHz, on the Synthesizer board, and applied as the reference signal to the mixer on the Offset Mixer board.
Theory of Operation - 4g4A/4g4Ap Service, Vol. l puter tunes the l st LO frequency through the following sequence; up 750 kHz, down i.5 MHz, up 1.5 MHz, ani down 750 kHz. During one of these yirmware searches,' the lst LO frequency passes through the strobe har- monic frequency and th€ loop acquires lock.
I t a o o a a t o o o t I o o o a o o I o o o o o o o o o t a o I o a I t I t o I o a o Theory of OperaUon - 494Al4g4Ap Servtce, Vot. 1 Output Amplifier LO AIIPLIFIER 4416-200 Flgute 7-27. Slmplified schematic of harmoolc mixer. Two additional directional couplers are used to cou- ?f.
Theory of Operation - 4g4A/494Ap Service, Vol. 1 PHASE/FREO DETECTOR fr:t,orF:NF, Figure 7-28. Block diagram of a baslc syntheelzer. Phase/Freq DETECTOR mOD CONTROL F,n : (NP + A) Frct o a t o I o o o o o t o o o o o o o o I o o o a o o o o o a C a o a o I o a o O o a o O Figure 7-29.
This synthesizer uses a variable modulus prescater to divide the VCO frequency before is processeO by the "+N" counter, such as shown in Figure 7-29. The vari_ able. modulus prescaler is iontroilej by a moclulus con_ trol input. When the line is high tne pr6scater is a divide by P+l and when the tine is l6w the division cnange" to P.
Theory of Operaton - 4g4Ll4g4Ap Service, Vol. 1 CR2068. CR1065 provides a clamp to prevent a control line voltage less than 5 V. Capacitor C1070 sets the low end of the control voltage to about 6 V. Range of the control voltage, over the 20A-Z2O MHz VCO ,ing", is about *6 V to +11 V.
DBl-ThE N LATCH signat for the lst LO phase tock is sent on this line. DB2-Reserved for future apptications. DB3-This lin€ resets the buffer sequencer at the outsEt of a talk cycle for the counters. DB4-This tine (CONTROL LATCH) tatches a conrrot word into the output buffers ot VZOZS on the Error Amplifier board.
Theory of Operaton - 4g4[l4g4Ap Service, Vol. 1 The Synthesizer can be divided into three functional blocks: the 100 MHz divider, the SO MHz divider, and the -+N counter. The 100MHz divider consists of flip-flop UgOgOA and transistors Q3040 and e3041.
U10508 witt ctock first, placing a high at the Error Amptifier,s inverting input. This iamps it," "*ptiR", ort- put low untit U1050A switches d "iiort time tater. U20508 resets both flip-flops anO tne inner toop error amprifier wiil stop rampin! untir the next correction cycle.
Theory of Operation - 4g4[l494fup Servlce, Vol. 1 drifts negative, the other half of UlO.l5 conducts, caus_ ing reverse action to occur. - Normally, the input signal to the window comparator is attenuat€d by R2040, which reduces the voltage applied to U101S to 0.
...Ttg V_CO output !g apptied to the ctock input of divide-by-s counter UaZZ. 'The STROBE'er.raeLe fin" frgm tlte Error Amplifier permits the counter to operate when the line is low and is the means by wnich the microcomputer can turn the strobe pufsed on or off.
DIGITAL CONTROL (Diagram 9) The Digital Control section provides operator and digital controller interfaces. lt translates changes in front-panel controls and, for the programmable version, also translates instructions received via the GplB into codes that control the instrument.
Theory of Operation - 4g4Ll4g4Ap Servlce, Vol. 1 o o o o o o I o o o I t o o o o o t o a o o 3 O o t t o I o o o o I t o o o a o o ) o o 8000 7800 7000 4000 0000 Figure 7-30.
Theory of Operation - 494A/494Ap Servlce, Vol. 1 DTA PFESENT DT REOUEST ilA GRANT feoc SWP CATE TMER sNO oPrg sRo SER RgO PWR FAIL lililililll NEAR PANEL GP|a SIVITCH (P VERStOfl ONLYI -__ ,-7 Llllllu.
o o o o o o a o o a I o o I a o t o o o O a o a o t o o o I o o o I o o t o a o o c o I Theory of Operation - 4g4hl4g4Ap Service, Vol. 1 Figure 7-32. PIA and Timer address map, 6821 PIA REGTSTERS OATA VALID 0{sTRUt|€XT D^TA AUS POLL II{STRUTIENT AOOR€SS BUS AODRESS RANGE !O.
Theory of Operation - 494A/4g4Ap Service, Vol. 1 Clock. This circuit generates the clock signat that drives the microprocessor, the GplA transceivdr on the GPIB board (A56), and the character generator circuitry on the CRT Readout board (A66A1). Y1030, Q2035, and e1030 form a clock circuit that oscillates at 3.
a o a a a a o o a o o I o o a I ) o o o o , o I o o t o I I I a o o o o o o o o a o I o GPIA interface circuit on th€ GptB board (A56). (Ihis only occurs on the programmable version.) Before each transf€r, the microprocessor loads U1020 with the starting address of the RAM data and the number of data bytes to be transferred.
Theory of Operation - 494Al4g4Ap Service, Vol. 1 lf the PwR FAIL line returns to a high state before the microprocessor is reset, the microprocessor does a power-up initialization to ensure that the instrument operation will not be affected by a temporary power loss.
o a o a o a t I o o I t o o a I ) o a o t a o a o C t o t o t o o a a a t o o o o o o o lithium battery 8T2040, or in option 3g, silver batteries (Eveready 392 or equivalent). See the Maintenance section for replacement information. Each ol the non-volatile memory lcs require less than 2 rl.
Theory of Operation - 4g4[l4g4Ap Servlce, Vot. 1 ROM. The ROM in this instrument is located on this board and on th€ ROM Banks & GptB board (A56). The ROM consists of system ROM containing the instrument operating system and the program RoM containing the various measurements routines and crt messages.
o o o o o o o o o a a o o o o o o a o , o o o o o t o o I o a o I o o a a I o o o a o o Accessories lnterface (Diagram 44) The Accessories lnterface board (A90A76) provides access to the instrument bus, and the external MARKER/VIDEO input and controt tine.
Theory of Operaton - 4g4[l4g4Ap Servtce, Vot. 1 appropriate action. Th€ following is a description of the hardware and a brief description of the software used bythe front panel CPU. Potentiometers. The following controls or adjust- ments generate analog signals used by other functions of the instrument.
O o o o o o o o o o o a o o o o o o o o O o o o o O ) o a o o o t o o o o o O o o o o o will see a phantom closure at y2lxg as it scans the key matrix. To suppress these piantom key closures, diodes have been added in series with the RESOLU- noN BANDWTDTH, MtN RF ATTEN, SpAN/D|V, and gerta]l other keys in column 6 and 7 of the k'ey matrix.
Theory of Operaton - 494[l4g4Ap Service, Vot. 1 Keyboard Check Subroutine. This subroutine is called when the main scan routine detects a change in the keyboard matrix which occurs when a key opens or closes.
Theory of Operation - 494A1494Ap Sewice, Vot. .t DATA ENTRY kHz/-dBX 5 1 6 I HzldB MHz/+dBX ROW o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o a o o o o o o o 2 4 3 7 X1 X1 X1.
ROW coL HEX CODE MAIN FUNCTION <BLUE.SHIFT> FUNCTION <GREEN.SHIFT> FUNCTION DATA ENTRY X6 X6 X6 X6 X6 X6 X6 Y1 Y2 Y3 Y4 Y5 Y6 Y7 32 33 34 35 36 37 38 MIN RF ATTEN dB 0 10 20 30 40 50 60 X6.
Theory of Operation - 4g4A/494Ap Servlce, Vol. 1 o o O o o o o o o O o o o o o o o o o O o o o o o o o o o o a o O o o o o o o o o o o o POWER SUppLy (Diagram 10) The Main power Supply furnishes all the regulated voltages for the spectrum analyzer, exc€pt the crt high- voltage :uppty.
Theory of Operaton - 494A/494Ap Servtce, Vot. 1 u$36. PrN 2 u603A PIN 3 u6036, P|l{ 7 Figure 7-34, Primary .egutator Input and output waveforms. a o o O o o o a o o o o o o o a o o o o o o o o o o o O o o a o o o o o O o o o o o a o Ramp Generator. The ramp generator circuit is a gated sawtooth generator that consists of T6044.
O o o o o o o o o o o o o o o o o o o a o o o o o o o o o o a O o o o o o a o o o o O o Theory of Operation - 494[l4g4Ap Servlce, Vot. 1 Flgure 7-35. Tirning waveforms for soft-start clrcuit Inverter Driver. The inverter driver consists of transistors Q6072 and e6079, transformer T60g1, and related components.
Theory of Operation - 4g4Ll4g4Ap Service, Vot. 1 Secondary & Fan Drive Circuits (Diagram 47) The secondary circuits include the rectifier_filter cir- cuit, which rectifies and filters the secondar.
o o o t I o o o o o a o O o a o O o o o o o o o o o I a o o a a o a o o a a a o o o a o Fan Drfve Circuit The fan drive circuit provides a temperature- con- trolled current drive to the fan motor. if,e circuit pro- 1y:?: " thr€e-phase_drive culent of approximatety 240 Hz operating freguency.
o o o o a o o o o o o o o a o o o o o o o t o o o o o o o o o o o o O a o o O o o o a o.
o o a I o o o a o a o o o I O o o o o o o o o o o o a o o o o o o a o o o a o o o o o o OPTIONS This section describes the options available at this time .- for the spectrum analyzer. Ct.ng"" in specifications,.if any, are described in this section.
OPTION 07 ALTERNATE SPECIFICATIONS Within 2ao/o ol selected bandwidth *2.0 dB about the midpoint between two extremes +20 dBmV *0.5 dB at 100 MHz Optons - 4944/494Ap Servlce, Vol. 1 Option 07 (75O Inpur) Option 07 provides an optional 7SO input and *20 dBmV calibrator in addition to the standard 50O input and +20 dBm calibrator.
o o a o o o o o o o O o o I o o O o a o o o o o I o o o I o a o o o O o a o o o o o o I Optons _ 494Al4g4Ap Servtce, Vol. 1 Tabtc B-2 (Continued) OPTION 07 ALTERNATE SPECIFICATIONS tS.4GHz to l2 GHz. bl2 GHz to 1g GHz. Options 21 and 22 (Waveguide Mixers) Option 21 includes a set of hrvo high-performance waveguide mixers (18 to 40 GHz).
Optione - 494A/494Ap Service, Vot. 1 Option 39 (Sitver Battery) . Option 39 provides a silver battery for the instru_m€nt's battery-powered memory. The battery life at +55"C is 1-2 years and 2-5 years at +2SoC. W€ recommend removing the silver batteries during long- term storage.
o a a a o o o o o I o o o I o o o o o o a o o o I o a o o O a o a o I I a o a a O o o a Opdons _ 494A/4g4Ap Servlce, Vol. 1 Tabte 8-5 OPTION 42 ELECTRICAL CHARACTERISTICS Characteristic Performance Re.
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o o a a O o a I o t o O o o I o a t o o a o o o o a a o o o a o o o o O o t I o o o o I GLOSSARY .._-Il"^^1"_l':,*ing gtossary is presented as an aid to understand the terms as they aie used in thi" do"urn"nt and with reference to spectrum anatyzers.
FREQUENCY TERMS Display Frequency. The input frequency as indicated by the spectrum analyzer and expressed i; hertz. Frequency Span (Dispersion). The magnitude of the frequency band displayed, expressed in-hertz or hertz per division. Frequency Llnearity Error.
o o o O o o t o o t o I o O o o o I o o O o o a o a o o I O I o I o o I I o o O o o o I Sensitvity. Measure oJ a. spectrurn analyzef s ability to display minimum rever signars, "*pi".J"o in vorts or decibets. Intermediate. tr"qu"n"V -ifei bandwidth, display mode, and any other innueniinji"'.
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o o a o o o o I I o O I o o I o o I o o O o o O a a t o t a I o o O a I I o I o o O o I REVISION INFORMATION Manual Part No. 07G556O-00 Flrst prtnilng JAN 1987 hduct Revleed Manual Insert Status CHANG.
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Tektronix. Cornnt|ncd to Ercdl€E Date:9-1-87 Product: See list MANUAL CHANGE INFORMATION Change Reference: C1 1887 Manual Part No: See list product Group: 26 INSTRUMENT 494N494AP Op€rators 494N4944P Service 1 Part No. 070-s557-01 070-5560-00 gN 8010227and up Feplaca sanshlvlty table In the speclflcailon secilon wlth the tabte betow.
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Tektronix" Cdmfrittsd to Erca{ence Date:2-22-88 Producl: see list MANUAL CHANGE INFORMATION Change Reference: M6391 1 Manual Part No: see list product Group: 26 I a I o o a o a o I o o o o a o o .
Product: see list Date:2.22-88 Chg. Ref. M63911 J. Set the Spectrum Analyzer controls for a lriggered sweep, then switch the sweep oft by activating SINGLE SWEEP, and ensure READOUT is on. K. Monitor lhe drains (metal tabs) of 04040 or Q4030, on lhe dellection Amplifier board, with test oscillo- scope.
o o I o o o o o o o o I o o I o o I o a o o o o o t o o I o I O o o t o o o I o o o o I Product: see llst date:2-22-88 Chg. Ref: M6391r Replace the description for the Deftection Amptifiers (Diagram 27) with the tottowing. DEFLECTION AMPLIF|ER (Diagram 278) Refer lo ihe block diagram adjacenl to Diagram 27 as well as the schematic diagram.
Product: see llst Dale:2-22-88 Chg. Ref: M63911 The standing cunent on the horizontal amplifier Moslets is established by a resistive divider R4046, R3045, and R5038 as lollows. The base of Q5040 is set 3.5 volts negative wilh respect to the +300 volt supply.
Product: see llst Chg. Ref: M63911 Replace tigure 5-6 in the Adjustment procedure section with the following diagram Figure 5-6. Deflection Amplifier test points and adjustments o o o o I a e o o a o .
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-^l-.r-- - r teKtrontx, Conmined to Erca$eno Date:5-1G-Bg Product: See List ITIANUAL CHANGE INFORMATION Ghange Reference: C2t5lgg Manual Part No: See List product Group: ZO PERFORMANCE CHECK PROCEDURE.
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Tektronix. Cottrti.d to Ercrltono Date: $01€8 Product: See list MANUAL CHANGE INFORMATION Change Relerence: M66071 Efi/SN 8010100 Manual Parl No: See list produci Group: 26 o a o o I o o a o o o a o.
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Tekt"fp"n[X. Date: 5/u9o Product: 494N4g4Ap Service Vol. 1 MANUAL CHANGE INFORMATION Change Reference: C2lSgO ManualPart No. 070-5s60-OO product Group: 2E In section 4 - PERF)RMANCE )HECK pRocEDURE change step r r as foltows: Replace header secfian with the foltowing: 11.
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Tektfgnl;. Date: 6/1190 Product: 494N494Ap Service Vot. 1 MANUAL CHANGB INFORMATION Change Reference: CA59A (revised) ManualPart No.070-5560-00 product GrOup: 2E o o C o O' o o o o o o o o o o rf a I o t o o o a o o o o I t t I I o o I C I a o I o I o The followlng is a revision of change Reference: c2ls90 datect slztgo.
Change stepll as follows: 6. Check Reslduat FM [Within 7 kHz over 20 ms with the 1st LO unlocked (SPAN/DIV >200 kHz for band 1 and bands 5 rhrough 12 and SPAN/DIV >100 kHz for bands 2 rhrough 4)1.
(2) Acrivare MARKER MENU pushbutton. (3) Select "7 - ENTER BANDWTDTH NUMBER" (4) Enter'60" with the keypad and terminate wilh "d8". (5) Activate BAND WIDTH mode pushbutton (<green_ sHIFT>BAND WTDTH). (6) From the information displayed on the CRT, record the 60 dB bandwidth in Tabte 4A.
RESOLUTION BANDWIDTH 3 MHz 1 MHz 6 dB BANDWIDTH LIMITS 60 dB Bandwidth RESOLUTION BANDWIDTH VERNCAL DISPLAY FREOUENCY SPAIVDIV 60 dB MEASURED BANDWIDTH Caleulated Shape Factor (60 dB/6 dB) SHAPE FACTOR SPECIFICATION 3 MHz 10 dB/ l MHz <7.5:1 1 MHz 10 dB/ 1 MHz <7.
o o a a o t t - - o t o t0 I o a o o I o a C a o C I o t a I a I a o a t a o 'a a a o a I t Change step 12 as follows: 12. Check Calibrator Output (-20 dBm r0.g dB) a. Apply an external 100 MHz signal to lhe power meter through a 3 dB attenualor and a 50e iable.
o a o o a o ^ r J o I t I o o a o o o o I , o I o t o o o a a a I a I o I I o I t t o I t Figure 4.14. RF attenuator test equipment setup, Change step 14 as follows: 14.
Tercfgnix MANUAL cHANcE INFoRMAnoN CETvitTTEDT oEcEu.E^pE Date: l1_Sep_gl Product: See List . Change Reference: C1-991 Manual Part No.: See Lisl DESCRIPTION Prodrrct Group 2E o o o o o o ? I o a o t o.
Product: See Llst Date: 11 Ref. C1-991 Spectrum Analyzer Under Test Test equlpment,setup lor checklng I dB lnput compresslon polnt- b. Sefect lhe following settings for the specirum anatyzer: FBEQUENO.
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An important point after buying a device Tektronix 494A (or even before the purchase) is to read its user manual. We should do this for several simple reasons:
If you have not bought Tektronix 494A yet, this is a good time to familiarize yourself with the basic data on the product. First of all view first pages of the manual, you can find above. You should find there the most important technical data Tektronix 494A - thus you can check whether the hardware meets your expectations. When delving into next pages of the user manual, Tektronix 494A you will learn all the available features of the product, as well as information on its operation. The information that you get Tektronix 494A will certainly help you make a decision on the purchase.
If you already are a holder of Tektronix 494A, but have not read the manual yet, you should do it for the reasons described above. You will learn then if you properly used the available features, and whether you have not made any mistakes, which can shorten the lifetime Tektronix 494A.
However, one of the most important roles played by the user manual is to help in solving problems with Tektronix 494A. Almost always you will find there Troubleshooting, which are the most frequently occurring failures and malfunctions of the device Tektronix 494A along with tips on how to solve them. Even if you fail to solve the problem, the manual will show you a further procedure – contact to the customer service center or the nearest service center
