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Model 420 Frequency Control Unit is designed for full bandcoverageof 80, 40, ZO, 15, and 10 meters, through twenty 200-kc segments. The unit is specifically intended for fixed and portable operation but may also be used for mobile operation, if space pernrits . CIRCUIT THEORY Q1, the 2N706Oscillator, operates in the Common base configuration as a Colpitts oscillator. See Figure 7. Capacitors C1901and C1902are in paraliel with C1931, the main tuning control, across the c o i l , L 1 9 0 1 . C a p a c i t o r sC 1 9 3 3 , C 2 0 0 1a n d C 2 0 0 4 effectively tap the oscillator across only about 10 percent of the tank circuit. 'fhis results in exceptional stability. Q2, the Emitter Follower, is used for matching the impedanceof the coaxial cable to the transceiver, not for stability purposes. Bandswitching is accomplishedby tapping the main coil L 1 9 0 1 , a n d p r o v i d i n gv e r n i e r a d j u s t m e n t s o i l s , c L1902 through L1921 for setting the low end of the tuning range. C1932provides vernier dial setting when using the crystal calibrator. INSTALLATION Model 420 is furnished with a mounting base for common mountingwith the transceiver. The Frequency Control Unit may be mountedon either side of thc transceiver. ALICNMENT Alignment of the Model 420 requires only the use of a general coverage receiver tuning the frequency ranges between 8 mc and 24 mc. Calibration of the receiver is not critical since the crystal calibrator in the transceiver is used for final adjustment, but the receiver must be accurate within 50 kc to permit selection of the proper 100 kc harmonic. Vernierdial set alignment may be made with the dial set knob. which may FORMINORFREQUENCYADJUSTMENTS, be required after the initial aging period, simply remove the cabinet cover and very carefully adjust the trimmer capacitor marked for the specific range.
FOR MAJOR FREQUENCYADIUSTMENTS Tune Frequency Controi Unit to low end of frequency range, and locate heterodynewith general coverage receiver at frequency indicated in following table with dial set at midpoint (dot straight up), adjust vernier coil to bring heterodynewithin a few kc of the receiver frequency, then switch on calibrator and adjust vernier coil for zero beat with calibrator. Move tuning to high end of tuning range and adjust trimtner capacitor for zero beat. Repeathigh and low end adjustments until calibration is correct at bothends. Coil and capacitor locatioris are marked in the unit BAND RCVR FREQ. (kc) 8573 8773 8973 L 2 ,1 7 3 L2,373 8827 9027 9627 15,827 76,027 16,227 22,927 23,027
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ADJUST ADJUST COIL CAP. (low end) (high end) L192r LI92O
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