Motorola GP68, Service Manual

Page: 28 / 85

2-8
6881086C09-O March, 1997
Theory of Operation GP68 Portable Radios Service Manual
The GP60 Series Radio Alignment Procedures
Low Port Modulation
Tuning Frequency:
Automatic - Frequency displayed on Tuning screen.
Deviation Setting:
375 Hz +/- 40 Hz for 12.5 kHz channel spacing,
750 Hz +/- 40 Hz for 20/25/30 kHz channel spacing.
• Set the radio into TX low power mode. The Modula-
tion Analyzer should be set as follows:
• Use the up/down arrow keys to change the low port
deviation setting and the F6 key to toggle the PTT.
NOTE
The low port tuning tone is automatically
generated internally by the radio. No external
modulation injection is required.
VCO Deviation Adjustment
Tuning Frequency:
Automatic - Frequency displayed on Tuning screen.
Deviation Setting:
2.2 kHz +/- 100 Hz for 12.5 kHz channel spacing,
4.6 kHz +/- 200 Hz for 20/25/30 kHz channel spacing.
• Set the radio into TX low power mode.
• Inject a 110 mV rms, 2 kHz audio signal into the
external mic using the radio test box.
• The Modulation Analyzer should be set as follows:
• Use the up/down arrow keys to change the deviation
setting and the F6 key to toggle the PTT.
Transmitter Power Adjustment
Tuning Frequency:
Automatic - Frequency displayed on Tuning screen.
Power Level:
VHF - 1 W and 5 W,
UHF - 1 W and 4 W.
• For power tuning, it is important to ensure that the
DC Voltage MUST be maintained under load at 7.5
V +/- 0.1 V (3 A is the current limit).
• Use the up/down keys to change the power setting
and the F6 key to toggle the PTT.
• Tune the radio according to the specification above.
NOTE
To avoid heating the radio too much, do not
leave the radio in TX mode continuously and
leave a 30 second interval between tuning
points.
Reference Oscillator Warp Adjustment
Tuning Frequency:
Automatic - Frequency displayed on Tuning screen.
Frequency window:
VHF = +/- 300 Hz,
UHF = +/- 400 Hz.
• Set the radio into TX low power mode.
• Use the up/down arrow keys to change the frequency
setting and the F6 key to toggle the PTT.
FM
PEAK+
15 kHz LP Filter “ON”
All HP Filters “OFF”
De-emphasis “OFF”
FM
PEAK+
15 kHz LP Filter “ON”
All HP Filters “OFF”
De-emphasis “OFF”