Tektronix 494AP service manual A o o o

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. f. Adjust Band 2 Gain RgOg4on th€ vR Mother b.oard #2 (Figure 5-241 tor a fult screEn (_20 OBml display.

_ g. Chang€ th€ FREQUENCYRANGE to 3.0_ 7.1 GH.z(Band3) and apptya catibrated_20 dBm sig- nal with the samefrequencyas notedfor the meanlevel in Band3 for part a of this step.

h. set the FREQUENCyto the incomingsignatand FFEOSPAN/DIVto 500 kHz/Div

i. AdjustBand3 GainR3030(Figure5-24)for a futl screendisplay.

j. Repeat the above procedure for €ach coaxial band (1-5) and set the gain of eachwith the appropri- ate adjustment. lf the range of any adjustmEntis insufficlent,add or r€movea diodebetrr,leen'pinDD and

th€adjustmentpotentiometer

-appfopriateon th€ vR Mother board #2. to obtain the reguiredrange. Refer 19 .th: schematicdiagram and componenttocatorfor Variable Besolution Mother goarOs, in Volume 2. Addingthe diodeincreasesgain.

15. Adiust Band Leveling for Waveguide Bands (Bands 6-11)

(R3024,R3026, Rg02g, R9029, anct R3032 on the VR Motherboard #Z)

?. I:g! equipmentsetup is shownin Figure5-23. Apply 2072MHz at -€OdBm, through a dt_btocking capacitor to the EXT MIXER input. Monitor the inpui with a pow€r meter to set the pow€r tevelthen add a known 30 dB attenuator so th€ input level to the

'Set

EXTERNALMIXERport is -60dBm. ttreSpectrum Analyzercontrolsas follows:

FREQUENCYRANGE 1g_26 GHz(Banct6)

FREOSPAN/DV 200 MHz

AUTORESOLN On

REFLEVEL-3OdBm

The baselineof the displaywill rise when the 2072MHz signat is apptied to the EXTERNALMTXERinputport connector.

b.With-60dBm input levelapptied,adjustBancl6 Gain Leveting R3024 (Figure 5-24) lor iuil screen display.

c.changethe FREQUENCYRANGEand inputsig- nalfrequencyand levelas listedin Table54, andadjuit the appropriateBandGainadjustmentsfor a fult screen display. Gainadjustmentfor the waveguidebandsneed to be adjustedonly if thesebandswill be used.

d.SwitchPOWERoff; replaceVariableResolution module,thenswitchPOWERbackon.

Adru3tmentProcedure- 4g4rl4g4Ap ServiceVot.I

Tabte 5-4

EXTMIXERBAND

LEVELINGADJUSTi,IENTS

	Band		Gain
			AdJustment
6 (18-27		GHz)	R3024
7 (26-40		GHz)	R3026
8 (33-60		GHz)	R3032
9 (50-90		GHz)	R3029
10 (75-140 GHz)			R3028
11	(110-220 GHz)		R3028
12	(r7O-325 GHz)		R3028

16. PhaseLock Calibration (C1016,C1018,C1032,and C1034on the Strobe

Driver board; C10i3 and C2011 on th€ Controlled Oscillatorboard; and Rl06l and R3Og2on the Error Amplifierboard)

The PhaseLock assemblynormallyrequirescalibra- tion only after some part of the assemblyhas been repaired or replaced. phase noise, producedby the phase lock loop, is specified tor -7AdBcor better, 3 kHz out from the response.This shouldbe checked beforecalibratingth€ assembly.

a.Test equipmentsetup is shown in Figure5-25.Removethe Phas€ Lock module and the two cover plates so all circuit test points and adjustm€ntsare accessible.Plugthe assemblyon extenderboardsand into the instrument.Use Extendercablesand adapters to reconnectsignal cablesto their respectiveconnector (cable with yellow band to J501, and the cable with blackbandto J502).

lf d€sired, the direct reading counter may be con- nectedto the VerticalOutputof the t€st oscilloscopeto get a count of a display at each test point, when appropriate,throughoutthis procedure. The ground

side of the test oscilloscopeprobe will serv€ as the commongroundreturnfor both instruments.

b.Press <Blue-SHIFT> CAL and do the directed calibration routine through adjusting the LOG CAL. Press <Blue-SHIFT> to return the instrumentto nor- mal operationand set REFLEVELto -30dBm. Check that the AUTo RESoLNis active(buttontit).

c.Check O{fset Mixer - This part of the pro- cedure is only requiredafter repair or replacementof the Mixer board.

(1)Connect the Direct Input of the frequency counter to pin N (Figure5-26) and set the counter controlsfor a count. Notethe frequency.

(2)Connectthe counterto pin K and notethe fre- quency.

5-25