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Preparing the 2nd LO Assembly lor Adjustment

..	T_":!	setupis shown		in Figure6-19. Turn
	_"guipment
the POWERoff. Rernovethe cabinetand place the
SpectrumAnalyzer_upsideOownio-inenf Oect<is
exposed. Use a 5/16 inch wrench to loosen and
remove the two semi-rigidcable connections
assembly. Remove				to the
			the flexiblecoaxialcable connec_
tionto the't00
	MHz input.

Removethe 14 screws that hotd the cover on the mu-metafsection and remov€ the cover. Unsolderthe feads to feedthrough capacitors CZidS and CZ2O4. fl'heseare the center two feedthrougfr

lerminals that feedthroughthe circuitboard,as strovinin'figureO-iOj

Replacethe cover usingtwo or threescrewsto hotd the coverin place.

Remove the mounting screws for the 2nd LO 131e1OtV.Carefuly tift the 2ncrLO assembtyfrom tnl chassis and turn it over so the machin€daluminum housingis up. Be sule that the pawer input

tions remainintact. place the ars"ruty on a "onn""- flat sur- I"9:: U1e a 5/64 Ailen wrenchto removethe screws

holdingthe lid on the machinedatuminumhousing,and r".T9ug.the tad,exposingthe three RF circuit boards withinthe osciffatorsection.

Installa 50O terminatoron the 21g2MHz buffEred output port, p222, (seeFigure6_21).

2. Adjust 2nd LO Frequency

(2182 MHz *t MHz)

a. Connect the test equipment as shown in Figure6-19.

b. Set the variablepow€r supplyto 0 V. Connect the plus posifive(+) terminatto ttri'enOLO housingand the.ne-gative(-) terminal to the exposeOLno ot CZ2OI and L2031,througha 1 kO resistor.

c. Apptya 100 MHz, 0_dBmsignalfrom the signat generatorto the 100MHz Referenieinput port, p221. (Frequencymustbe within20 kHz of 10OMHi.)

d. Connectthe test spectrumanalyzerto the 21g2 MHz.unbufferedoutput port, p220. tni" is the test spectrumanalyzerwith the referencefrequencyposition

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THE CABLESOVERTHE 2ND LO ASSEMBLYOSCIL- LATORSECTIONBECAUSETHEYCAN AFFECTTHE FREQUENCYOF THEOSCILLATOR.

e.Bendthe feedbackand frequencyadjustingtabs, C1021and C1922(C and D in FigureO'-Ztisothey are approximately30 degreesabovethe boardsurface.

-f. Applypower to both the SpectrumAnalyzerand the variablepower supply. Set the voltageoutput from the variabtepowsr supplyto 5.0V. Votiige on C2203 shouldnow equal,-SV and a signalstrout-appeartOonthe test spectrumanalyzer.

Maintenance_ 4g4[l494Ap ServtceVot.1

g.Check for a voltageof *10.0 V, r0.7 V across c2023.

h.CheckVbe at Tplols (B in Figure6-21). tf Vbe ls greater than +0.9 V, push the feeabackadjustment tab down stightlyand it tessthan _0.9 V, tift tha tab. lf Vbe is greaterthan +O.gV, replacethe microstriposcil- lator board. lf Vbe is more negativethan _1 V, check th:9T circuitry. Adjust tne iaO so Vbe is +0.15V, t0.O5V at Tplois. Do not touch the feedbacktab whilEmeasuringvoltages.

i, Checkthat the 2nd LO signal(frequency)is within 9j'9-major division of the center Sratiiute tine (2.181GHz to 2.18itcHz). B,endthe freq-uencyadjust_ment tab c1022 (D In Figure6_21)to bring the oscitiator within tolerance. (Bend the tab up tt increasefre_ quencyand downto lowerfrequency.)

j. lf unableto bring the oscillatorfrequencywithin rry-ewith the adjustment tab, the frequency of the 2182MHz osciilatorcan be brought within range of the adiustmentab- by short€ninga transmissionlinestub(A in Figure6-21).Graduationmarksalongthe sideof the stub providea guideto calculatetrequencycorr€ction. Each minor mark from the end or cui acrossthe stub, representsan approximatechangeof 25 MHz.

k.Checkthe frequencyby notingthe t€st spectrum analyzerdisptay. tf the frequencyis too high,ihe stub must be lengthenedby solderinga bridge acrossth€ cut. Recheckthe freguency. lf the frequencyis too low,the stub mustbe shortened

l.Shorten the line so the frequency is near 2200MHz. For example: The freguency difference betweenthe desiredand tho actualdivideOOyeSUH., equalsthe numberof minor divisionsfrom the lineend

for the new cut. Makea cut acrossthE line and check that the new frequencyis near 2200MHz. Repeatas necessary,the use the adjustmenttab to bring the oscillatorwithintolerance.

m. Check2182MHzoutputpow€r.

Before making power measurements, ensure that the unused port is t€rminated

into 50O. Unterminatedports will degrade both frequencyand powermeasurements.

(1)Check for 0 dBm +3 dB output power at the unbufferedport, P220.

(2)Connectthe test spectrumanalyzerto p222,ter- minateP22Oin 50e, then check for an outputlevel of +10 dBm *3 dB from the bufieredport.

6-35