Motorola GP2000 Service Manual page 34

3-2
3.0 Hardware Tuning Setup and Procedure
There is a silver seal on the bottom left of the radio chassis. Remove the seal to expose the two
potentiometers for audio and sub-audio (CTCSS) modulation adjustment. RV601, which is slightly
higher, is the trimmer potentiometer for audio modulation tuning. The lower trimmer potentiometer
(RV602) is meant for sub-audio modulation tuning.
3.1 Audio Modulation Tuning
1. Set the radio to transmit at 155.025MHz with low power. Set Channel Spacing to "CS-25.0"
for 25kHz (see Ò Radio Programming Ó on page 4-1).
2. On the test equipment, set it to receive at 155.025MHz and with the following conÞgurations :
Audio bandwidth : 0.25Hz to 15,000Hz.
De-emphasis : OFF
3. Inject a 60mV 1kHz tone to the radio through the extenal mic connector.
4. Key up the radio.
5. Using the ceramic tuning tool, adjust RV601 to tune the audio modulation deviation to settle
between 4.3kHz to 4.5kHz.
3.2 Sub-Audio Modulation Tuning
1. Set the radio to transmit at 155.025MHz with low power and Tx PL frequency of 100.0Hz. Set
Channel Spacing to "CS-25.0" for 25kHz (see Ò Radio Programming Ó on page 4-1).
2. On the test equipment, set it to receive at 155.025MHz and with the following conÞgurations :
Audio bandwidth : 0.25Hz to 3,000Hz.
De-emphasis : OFF
3. Do NOT inject any tone to the radio.
4. Key up the radio.
5. Using the ceramic tuning tool, adjust RV602 to tune the sub-audio modulation deviation to
settle between 0.65kHz to 0.75kHz.
RV601
Figure 3-2 Tuning Ports
Hardware Tuning Setup and Procedure
RV602