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Malntenance- 494A/494ApServiceVol. 1

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Four Cavlty Fllter-The characteristicsof the filter are checkedwith a network analyzer.Freguencyof the filter is 2A72MHz, bandpass,t-SUl-lzdown, is 1 dB, return loss is 20 dB or greater,and insertionloss is 1 clB. lf the seal is brokenon anytuningslug,adjustfor maximumreturnloss.

Mlxer*To gain access to the Bias adjustments, rernove the assemblyfrom its mounting;then remove the mounting ptate on the bottom of the assembly. Reconnectthe Mixerto the input/outputlines,usingthe same cables(cablelengthof semi rigid cablesis iriti_ cal). Appty the CAL OUT signatto the RF INpUTand tune a rnarkerto centerscr€en, Simultaneouslyadjust 99th bjas porentiometers,R1021 and R1022, liee Figure6-11)for maximumsignalamplitude.

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Table6-6

EOUIPMENTREQUIREDFORRETURNLOSSADJUSTMENT

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Test Equlpment

 

 

SpectrumAnalyzer

Frequency

MHz

SignalGenerator

range)110

+10dBmat 110MHz

 

VSWRBridge

 

 

10 dB & 1 dB Step Attenuators

50O, 0 dB to 40 dB

 

Termination

 

 

 

Adapter

 

 

RecommendedType

TEKTRONIX49X-Seriesor 7L14

TEKTRONIXSG503for the TM S0O-Series

Wiltron628F50

HewlettPackard355C& g55D

TektronixPartNo.011-0049-01

TektronixPartNo. 175-0419-00

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O

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Tll 50O M.ine F.rme

Test fg0-S€riesSpoctrum Anatyz€r

a{te76

Figure 6-9.110 MHz lF return loss adjustment setup,

6-27

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Tektronix 494AP service manual O o o o o o o o o o o o o O a o o, Malntenance- 494A/494ApServiceVol