Service manual
2000 SERIES RECEIVER DECODER MODULE (RDM)
3-15
March 2000
Part No. 001-3139-502
3.11 800 MHz RECEIVER ALIGNMENT
C R I T I C A L A D J U S T M E N T
The TCXO must be adjusted within 5 minutes of turn-
ing the power on to the RDM. Do not under any cir-
cumstances try to set frequency later on in any of the
tests, as TCXO frequency stability cannot then be
guaranteed.
Refer to Figure 3-30 or 3-31 for component loca-
tions. Refer to Figure 3-36 for equipment needed and
setup diagram.
3.11.1 PRE-TEST
1. Preset L201, L203, L204, L206, L223 and L224
tuning screws about 1/4 inch above the top of the
casting.
2. Preset L202 and L205 tuning screws just barely
above the tightening lock nuts.
Apply power to the Receiver by plugging the
20-pin cable from the RF Interface Board into J201
(see Figure 3-30 or 3-31).
Measure the voltages at the following pins.
U206, pin 1 - +12V DC ±0.4V
U207, pin 1 - +12V DC ±0.4V
U208, pin 1 - +6V DC ±0.2V
R309/R310 junction - +3.5V DC ±0.1V
3.11.2 PROGRAM TUNE-UP CHANNEL
1. Using the PC and software, program the Synthesizer
for the Receive channel number.
2. Tune the VCO helical L220 for +4.5V DC ±0.05V
on U209, pin 6 or TP2.
3. Alternately tune L223 and L224 in 1/2-turn to 1-turn
increments until a voltage is measured on J201, pin
13 or TP5. At that time, tune L223 for a peak, then
L224 for a peak.
4. Retune L223 and L224 for a peak at TP5.
NOTE: The Channel Number, Channel Frequency and
Synthesizer Frequency appear at the bottom of the
screen.
3.11.3 TCXO FREQUENCY ADJUST
1. Place a pick-up loop (sniffer) or RF probe connected
to a frequency counter near L210.
2. Set Y201 (TCXO) for the Injection Frequency
±50 Hz (Inj Freq = chnl freq - 52.95 MHz).
3.11.4 VCO TEST
1. The software programs the synthesizer for
3 MHz above the Receive Channel.
2. The voltage on TP2 should be < 7.5V.
3. Record the voltage on J201, pin 13 __________.
4. The software programs the synthesizer for
3 MHz below the Receive Channel.
5. The voltage on TP2 should be > 2V.
6. Record the voltage on J201, pin 13 __________.
7. If the voltages recorded in Steps 3 and 6 are not
within ±0.2V, tune L224 as required to balance the
voltage readings.
8. The software programs the synthesizer for the
Receive Channel.
3.11.5 FRONT END ADJUSTMENTS (REV. 5)
REVISION 5 OR EARLIER BOARDS
1. Set the signal generator to the Receive Channel at a
level sufficient to produce an output voltage on
J201, pin 7 (RSSI Output).
2. Tune L204, L205, L206, L201, L202, L203 and
L204 for a peak voltage on J201, pin 7. Decrease the
generator output level to maintain a 2-3V reading at
J201, pin 7.
3. Set the generator for 1000 µV into the receiver with
a 1 kHz tone at ±3 kHz deviation (100 µV at the
receive antenna with 20 dB pad at the generator).