Tektronix 494AP O o o o o o o o o o o o, PerformanceCheck procedure 4g4Ll4g4ApServiceVol

o o o o

PerformanceCheck procedure - 4g4Ll4g4ApServiceVol. 1

o o

E	-28(	o	a.	rotx
					f,

This calibrationshould be done at regular intervals so the instrumentcan meet its eenterfrequencyand referencelevelaccu_

o o o

O

o o o

I

I

t '

-t

{

{

{

-

-r

-

racy performancespecifi,cationslt. should also be done each time the ambienttem- peratureof the instrumentis changed.

To observethe resultsafter the microcom- puter has cornpleted a calibrationroutine, pressthe <Blue-SHIFT>LINseguence.Amessagewill appear on the screen that shows the correction factor used by the microcomputerto center the resolution bandwidthfilters to produce a calibrated centerfrequency. lt also showsthe correc-

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

I -

s	-ta
	.C DII
r

ssqx2

Figure -4-2. Typical display of catibrator signat In Max Span/Div.

CalibratePosition,CenterFrequency,Reference Level,and DynamicRange

Whenthe <Blue-SHIFT>CALsequenceispressed, the microcomputerpe*orms a center frequencyand referencelevel cali- bration. Promptsapp€ar on the screento guide .the user step-by_stepthroughthe procedure.

tion that was requiredto bring the ampli_ tudelevelwithin0.4 dB of the 3 MHzfilter.

Press the <Blue-SHIFT>CAL sequenceto start the calibrationroutine. A prompt messageon the screen will guide you through settingthe four front- paneladjustmentsof verticaland horizontalpOSlTlON,

and AMPLand LOGCAL. This sets thEabsolut€refer_ encelevelfor the 3 MHz resolutionbandwidthfilter. An automaticcalibrationis then done,whichmeasuresand correctsfor absolutefrequencyand amplitudo(r€lative to 3 MHz)errorsof the filters. tnis takesapproximately 60 seconds.lf a messageappearson the screen,rsfer to Error MessageReadoutearlierin this section. The correctionfactors are held in memory. press FINEto continuecalibrationas instructedor <Blue_SHIFT>to exittheroutine.

lf any amplitude correction factor for a fitter is greaterthan 1 dB. at roorntemperature,the tilterin the VR assemblyshouldbe readjusted.Referto SectionS. AdjustmentProcedure.

O 4-5

a o