MASTR II ICOMs should be reset only when the fre-
quency shows deviation in excess of the following limits:
A.
±
0.2 PPM, when the radio is at 27.5°C (81.5°F)
B.
±
1 PPM at any other temperature within the range of -
30°C to + 85°C (-22°F to + 185°F)
If an adjustment is required, pry up the cover on the top
of the ICOM to expose the trimmer, and use one of the fol-
lowing procedures:
If the radio is at an ambient temperature of 27.5°C
(81.5°F), set the oscillator for the correct operating fre-
quency.
If the radio is not at an ambient temperature of 27.5°C,
setting errors can be minimized as follows:
A. To hold the setting error to 0.1 PPM (which is consid-
ered reasonable for 1 PPM ICOMs):
1.
Maintain the radio at 27.5°C (81.5°F) and set the
oscillator to desired frequency, or -
2.
Maintain the radio at 27.5°C ( 10°C) and offset the
oscillator, as a function of actual temperature, by
the amount shown in the correction factor chart
(Figure 2).
For example: Assume the ambient temperature of
the radio is 18.5°C (65.4°F). At that temperature,
the curve shows a correction factor of 0.44 PPM.
(At 851 MHz, 1 PPM is 851 Hz. At 875 MHz, 1
PPM is 875 Hz.)
With an operating frequency of 851 MHz, set the oscilla-
tor for a reading of 374 Hz (0.44 x 851 Hz) higher than the
licensed operating frequency. If a negative correction factor
is obtained (at temperatures above 27.5°C), set the oscillator
for the indicated PPM lower than the licensed operating fre-
quency.
TRANSMITTER ALIGNMENT
EQUIPMENT REQUIRED
1.
GE Test Set Model 4EX3A11 or Test kit 4EX8K12.
2.
A 50 ohm wattmeter capable of dissipating 150
Watts connected to the output terminal of the PA as-
sembly.
3.
A frequency counter.
PRELIMINARY CHECKS AND
ADJUSTMENTS
1.
Place ICOM on Exciter Board (crystal frequency =
operating frequency
•
48).
2.
For a large change in frequency or a badly mis-
aligned transmitter, preset all slugs to the top of the
coil form.
3.
Set Z101 and Z102 to top of coil form.
4.
Set both air variable capacitors to minimum capac-
ity (not meshed).
5.
Connect the red plug on the GE Test Set to the Sys-
tem Board metering jack, and the black plug to the
Exciter metering jack. Set the polarity to +, and set
the range to the Test 1 position (1 Volt position for
4EX8K12) for all adjustments.
All adjustments are made with the transmitter keyed.
Unkey the transmitter between steps to avoid unnecessary
heating.
Figure 2 - Correction Factor Chart
LBI-31985
LBI-31985
2
