TTI TCB-550, Руководство по обслуживанию

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4-3-6. Transmitter / Receiver Buffer AMP
The VCO output is fed into buffer AMP QW1 from the capacitor of CW1.
4-3-7. Transmitter Doubler
The output signal of QW1 goes to an amplifier tuning circuit(27MHz) QW2, LT1, LT2 which
doubles incoming 13MHz signals.
4-3-8. Switching of tuning capacitor in VCO.
The VCO circuit must turn with a wide range of frequencies 13.4825MHz - 13.7025 MHz for
transmitter and 16.27MHz - 16.710 MHz for receiver. The use of one tuning capacitor in common
has adverse effects as a decrease in C in the tuning circuit and the occurrence of may spurious.
To eliminate these effects, the tuning capacitance is switched for transmission or reception.
The tank circuit consist of the primary of LV1, CV1, CV4, CV6, CV7 when receiving QV2 becomes
off.
So. the primary of LV1 and make tuning function. when transmitting, QW2 becomes on.
So, the primary if LV1 and the parable capacitance of CV11 make turning function.
4-3-9. Receiver Local Oscillator Outputs
4-4. Frequency Stability
-First Mixer :
The output of VCO is injected through buffer AMP QW1 and than
The emitter follower output through the emitter of 1'st mixer or 2,3.
-Second Mixer :
The output of 10.240 MHz oscillator circuit with X2 is injected into the if IC of IC1.
Incoming if signal and 10.240 MHz signal are mixed inside the IF IC to 2'nd IF signal 455MHz.
FM audio signal are recovered with the way of quadrature detector.
AM signlas are recovered with envelope detector.
LET : Fo=Crystal Oscillator Frequency
4-5. Description of other circuits.
4-5-1. Transmitter
1. RF Amplification
THEN : Fvco= N X Fr = N(Fo/1800)
From which it can be seen, the percentage error in Ft is the percentage error in Fo.
The stability of the crystal oscillator is determined primarily by the crystal itself and having lesser
deviation by the active and passive components of the oscillator. The choice of crystal and
components is such that the required frequency stability is maintained over the required voltage and
tempertature range.
Fr=Phase detector reference frequency
Fvco=VCO frequency
Ft=Transmit freqency
THEN : Fr=Fo/1800
And under locked confitions : Fr =Fvco / N
Where N is the programmable divider divide ratio.