TTI TCB-550, Service Manual

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The output of doubler AMP QW2 is fed through double tuning(27MHz) LT1 and LT2 to the base
of PRE AMP QT2. The output is then supplied through tuning circuit LT3 to RF driver AMP QT3.
The QT3 output is capacitance divided by tuning circuit CT10, CT12, LT4, CT13 and passed through
the base of final RF stage QT4. The QT4 output is supplied to the antenna through L-C tuning circuit
(CT21, CT22, LT11, CT26, LT12, CT27, CT28, LT14, CT30).
The tuning circuit between frequency synthersizer and final AMP QT4 and 4-stage " PI"
network CT21, CT22, LT11, CT26, LT12, CT27, CT28, LT14, CT30 in the QT4 output circuit serve
to suppress spurious radiation. This network serves to impedance match QT4 to the antenna and to
reduce spurious content to acceptable levels in the frequency synthersizer.
2. Circuit for suppression of spurious radiation
After finished all alignment, the constant voltage supply circuit limites the available power 4W or
slightly less. Corresponding three-TR control supply voltage of RF power amplifier. When power
low S/W function QHL1 changed the supply voltage. Tune all the trimming parts for max indication
of RF power meter and adjust VR3 to make 4W indication of RF power meter. After finished the above
adjustment check the RF power meter reading is changed 1W under ' Low" state.
The tuning is adjusted so that the actual power is from 3.6 to 3.9 watts.
There are no other additional controls for adjusting the TX output power.
3. Circuit for Limiting Power
- AM
The MIC input is fed to audio power amplifier IC3 which drives modulation transformer TM1.
The audio output at the secondary of TM1 is fed the modulating audui signals series with the B+
voltage to the collectors of driver QT3 and TX power AMP QT4 to modulate both these stages.
A portion of the modulating voltage is rectified with DM1 which controls QM2 and QM1 to attenuate
the MIC input to MIC AMP IC3.
The resulting feedback loop keeps the modulation from exceeding 100 percent inputs approximately
40dB greater than that requires to produce 50% modulation.
- FM
The MIC input is fed to MIC audio amplifier IC7 that drives modulation varicap diode DV1,2 in the
VOC circuit RV3 limits the incoming modulation audio levels to inhibit over modulation. While
reading the modulation factor on the modulation analyzing equipment, adjustment RV3 shall not exceed
2.0 KHz deviation.
4. Modulation
4-5-2. Receiver
CB receiver is dual conversion super-heterodyne type with the first IF 10.695MHz and the
second IF 455KHz.
Receiver is separated two blocks, 1’st IF section and 2’nd IF section. The PLL synthesizer
supplies 1’st
With the provided first local frequencies QR2,3 mixes the incoming signal to generate first IF signal.
Mixed signals were filteres with the CF1(10.695MHz) crystal filter and tuned circuits.
With the 10.24MHz signal,IC1 FM IF IC converts the incoming signals to generate second IF signal.
2'nd IF is filtered by a razor sharp seramic filter CF3 coulpled.
The 455KHz signals from the 2nd IF filter were amplified and limits inernally. After amplification
the signals fed to the quadrature detector loop LR5. Than could see the recovered sifnals PIN 9
of IC1.
local frequency 16.270MHz ~ 16.710MHz.