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is completed and program customer frequencies. Use the low power channels for all VCO tests to
minimize overheating of the radio.
The VCO must be adjusted so that the phase detector voltage remains between 1V and 5 V over the
entire range of frequencies used.
1. To access the VCO, remove the top cover, 2 black screws, and the VCO shield, 5 brass screws.
2. Select the center channel which was programmed for tuning adjustments. Connect DMM to TP2
located on the left edge of the main board.
3. Adjust L301 located on the lower left, for 3 V in the RX mode.
4. Adjust L305 located on the lower right, for 3 V in the TX mode.
5. Check both RX ant TX VCO at highest and lowest frequency to make certain that voltage remains
between 1 V and
5
V. Make minor readjustments as required.
6. For frequency spread of less than 10 mHz, re-install VCO shield and top cover. For spread over 10
MHz, leave covers off for later adjustment of FVR3O1 Modulation Balance control.
5.2.2 RECEIVER TUNING ADJUSTMENTS
Note:
If no repairs have been made to the radio, the sensitivity may be easily checked by testing the
squelch sensitivity. Set the squelch to threshold and apply an on-frequency signal of .25 uV. If the
Squelch opens, the sensitivity is OK. Typical squelch sensitivity is usually <.2uV,
1. Connect one lead of the Analog AC voltmeter to the high side of the speaker at the rear connector,
pin 3 or 4 (jumper wire). Connect the other lead to the radio chassis.
Remove bottom cover, 2 black screws.
2. Connect signal generator to antenna connector, select center channel frequency.
3. Check that RX VCO voltage at TP2 is near 3 V (+/- .5 V). Recheck VCO adjustment if necessary.
4. Select the center channel and adjust L1, L2 and L5, L6 or BPF1 (depends on band) and T3 for
best sensitivity. Check sensitivity at the highest and lowest frequency and make minor adjustments if
needed. Note that there may be a slight difference is sensitivity on these channels but it should not be
outside of the sensitivity specifications.
5. After tuning is completed, sensitivity should be less than 0.4 uV for 20 dB quieting and less than .3
uV for 12 dB SINAD. Squelch sensitivity should be less than .25 uV at threshold.
5.2.3 FREQUENCY ADJUSTMENT
1. Connect frequency counter to the transmitter using proper attenuation.
2. Key the transmitter on a low power channel and adjust the trimmer on the reference oscillator OSC1
for correct frequency within 1 PPM. OSC1 is located on the front left side of the radio. This
adjustment controls both the TX and RX frequencies.
5.2.4 TRANSMITTER POWER AMPLIFIER ADJUSTMENT
Note: The mobile transmitter is designed for 20% duty cycle. Key the transmitter only long enough to
make the adjustments. The transmitter contains internal protection against overheating which may
reduce the power output if it is keyed for a long time. This may cause improper setting of the power
output and possible damage to the radio..
