Tektronix 494AP O a a a a o o o o a o o o o o o o o o o o, O a o a o a o o o, MIN RF Atten

AdiustmentProcedure- 494A/4g4ApServiceVot.1

10. Adjusf CalibratorOutputLevel

(R1041on the 100 MHz Osc and 3rd Converter

board)

The calibratoroutput level is matchedto a knownreference.A powermeteris usedto verifythe output level of the referencesig_ nal generator.Harmonicsof th€ signalgen_ erator must be greater than 40 dB down from the fundamental.

a.Applya 100MHz signalfrom the signalg€nera_ tor to the powermeter througha 3 dB attenuator.Set the generatoroutputlevel for a readingof -20 dBm on the power meter. This sets up a referencesignalfor adiustingthe calibratoroutput level.

b.Disconnectthe power meterfrom the signalgen- erator,and connectth€ refencesignal(fromthe genera- tor) to the test spectrumanalyzerRF INPUTusingthe samecablethatwas usedto set the referencesignal.

c.Set the test spectrum analyzercontrois as fol_

lows:

FREQUENCY	100MHz
FREQSPAN/DV	100kHz
RESOLUTIONBANDWIDTH	1 MHz
REFLEVEL	-18 dBm
MIN RF ATTEN	0 d B
VIEWA andVIEWB	On
PEAK/AVERAGE	FullyCounterclockwise
TrME/DtV	AUTO
TRIGGERING	AUTO

d.Set the test spectrumanalyzerVerticatDisplay factorto the A A mode by pressingFINE. Set the REF LEVELsuchthat the top of the signalis on a graticule line near the top of the crt. Resetthe REF LEVELto 0.00dB by pressingFINE twice. Store the displayby activatingSAVEA.

e.Removethe r€ferencesignalfrom the RF INPUT and connectthe cAL oUT signalin its place, Tunethe CENTERFREQUENCYcontrot to atign the CAL OUT signalwiththe SAVEA disptay.

f.AdjustCal LevetR1041,in the 3rd converter(#2 in Figure5-20)for no displacementbetweenthe CAL OUT signal and the reference(VIEWB and SAVE A displays).

5-20

11. Adjust lF Gain

(Rl015on the 110MHzAmptifierboard)

a.Test equipmentsetup is shown in Figure5-20. SEt thE RESOLUTIONBANDWIDTHtO 1 MHZ, REF LEVELto -20dBm, and VERT DISPLAYto 2 dB/DtV. Apply a -25dBm, 110MHz signat, through step attenuators,to the input(J365)of the 110MHz fitter.

b.set the step attenuatorsfor 0 dB. set the signal generator frequency {or maximurn amplitude display. With -25dBm input the signal level shoutdbe 7 divi- sions or more.) Set the generatoroutput for a 7 divi- sionsignalreferencelevel.

c.Removethe 110MHz signalfrom the 110MHz filterand reconnectP365.

d.Set the step attenuatorsfor 21 dB attenuation

and applythe 110MHz signalto the input(J321)of the '110

MHzlF amplifier(Figure5-20).

e.Adjust R1015,110MHz lF Gain, for a disptay amplitudethat equalsthe sevendivisionreferenceset in part b.

f.Removethe 110MHzsignaland reconnectP321. Apply the cAL ouT signalto the RF NPUT. set the SpectrumAnalyzercontrolsas follows:

FREQUENCY	100 MHz
FREQ SPAN/DIV	100 kHz
RESOLUTIONBANDWIDTH	100 kHz
REF LEVEL	-20 dBm
VERT]CAL DISPLAY	2 dB/DIV

g.Set the front panel AMPL CAL fully counterclock- wise and readjust Rl015 (110 MHz lF Gain) for 5 divi- sions of signal. (lf this cannot be achieved, it indicates excessive loss through the front end.)

h.Adjust the AMPL CAL for a full screen signal. AMPL CAL adjustment should now have 6 dB down range and 6 dB or more up range.

Two variablecapacitors,C1054 and C2047 on the 110MHz lF board,do not require adjustment during calibration. These adjustmentsrequire return loss measure- ment which is a maintenanceand repair function.

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