User Manual

SERVICING
5-5
Part No. 001-3422-003
5.3.6 MIXER (Q232)
The mixer converts the RF signal (132-174 MHz) to 21.45 MHz. The Local Oscillator is provided by the
VCO and Q302. The level of the LO should be approximately +3 dBm.
5.3.7 LNA (Q202)
The LNA provides approximately 16 dB of gain at 132-174 MHz. Q201 provides active bias to Q202.
5.3.8 PRESCALER FILTERS
The 2-pole and 3-pole LC prescaler filters limit the out-of-band signals from reaching the receiver. The 2-
pole filter has approximately 2.5 dB of loss and is composed of L201-L203, CR281/CR282, and C202-C207. The
3-pole filter has approximately 5.5 dB of loss and is composed of L212-L214, CR283/CR284, C214-C217 and
C221-C223. These filters are varactor tuned and require a control voltage to tune throughout the band. The
voltage on TP281 varies from 2.5V at the low end of the band to over 7V at the high end of the band.
5.3.9 ANTENNA SWITCH
CR561, CR562, L561, C561 and C563 form a Pi-network antenna switch. CR561 and CR562 are reversed
biased in Receive Mode.
5.4 TRANSMITTER SERVICING
5.4.1 SUPPLY VOLTAGES AND CURRENT
Measure the supply voltages on the following pins of interface connector J201:
Pin 2 - 13.3V DC nominal
Pin 3 - 3-16V DC
Pin 4 - 0.0V DC (while transmitting)
Pin 5 - 3-16V DC
Pin 6 - 2.5V DC ±1%/1.5V P-P max
Place a DC ammeter in the supply line to the transceiver and the following maximum currents should be
measured:
Pin 2 - 2.5A maximum
Pin 3 - 400 µA
Pin 5 - 400 µA