Maxon SP-1102, Руководство по обслуживанию, Страница: 22 / 35

Service Manual SP - 1402
Page 22 of 35
Detailed Functional Description
UHF Transmit
The transmitter is comprised of:
Buffer
Power AMP
Low Pass Filter
Antenna Switch
APC (Auto Power Control) Circuits
Buffer
VCO output level is 0dBm and amplified to +16dBm (UHF)/(VHF). The buffer consists of Q22, 12
Power AMP
The P.A Module consists of 2-stage amplifier (Q9,8) and amplifies the TX signal from +16dBm to
+30dBm. The input and the output terminal of the P.A Module are matched 50 OHM.
Low Pass Filter
L3, 2, 1, C196,C163,C71,C70 are the 7th order Chebyshev low pass filter. Unwanted harmonics
are reduced by -36 dBm.
Antenna Switch
When transmitting, the diodes D9 and D5 are forward biased enabling the RF signal passage to
the antenna. D5 is shorted to ground inhibiting the RF signal to front-end. In receive the diodes
D9 and D5 are reversed biased passing the signal from the antenna through L5 and C180 to the
front-end without signal loss.
Automatic Power Control Circuit
This circuit controls TX power by detection on the current through R21,11,103 The voltage
difference from these resistors are amplified by IC3-A and gets the voltage comparing the signal
with the reference voltage from R110 at IC3-B. This voltage difference is kept to stable value by
RV5 changing Gate voltage of final Amp (Q8) .