Compensation Alignment Procedure - Motorola Spectra Service Manual

V. COMPENSATION ALIGNMENT PROCEDURE
Compensation alignment balances the modulation
sensitivity of the VCO and reference modulation (syn-
thesizer low-frequency port) lines. Compensation
alignment is critical to the operation of signalling
schemes that have very-low-frequency components (for
example, DPL) and could result in distorted waveforms
if improperly adjusted.
Compensation alignment should only be required
after replacing (or servicing) the command board or the
RF board. Use either of the following methods, depend-
ing on test equipment availability.
The 1- kHz tone used to set deviation in procedure
IV. must not be connected during the compensation
adjustment, as it will sum with the 11Hz or 67Hz
tones.
A. Method 1
This method requires a modulation analyzer or
meter with a frequency response to less than 10Hz
modulating frequency. This is the preferred, more accu-
rate method. If, however, such test equipment is not
available, use method 2.
1. Connect the modulation meter to the antenna con-
nector, using minimum cable length and appropriate
power attenuators for the meter input level.
2. Connect dc power to the radio and switch radio
power on.
3. At the PC's "MAIN MENU" prompt, press F2 to
select "SERVICE."
4. At the "SERVICE" menu, press F4 to select
"ADVANCED ALIGNMENT."
5. At the "ADVANCED ALIGNMENT" menu, press F3
to select the TX Compensation screen.
6. At the TX Compensation screen, press F4 to key
the radio with an 11Hz tone modulation.
By pressing F4, "PTT 11Hz," you place the radio into
test mode 1, causing it to transmit on 896.0125
MHz. Microphone PTT should not be used during this
procedure, as it will cause the radio to transmit on
the mode presently displayed on the control head,
and will not generate the necessary tone.
7. Note the level of deviation on the analyzer and
press F4 to dekey the radio. (Use average devia-
tion, if available, on the analyzer.)
8. Press F6 to key the radio again. This generates a
67Hz tone.
NOTE
NOTE
9. Use the up and down arrow keys to adjust the com-
pensation value until the deviation is within ±+0.2
dB (2.3%) of the value noted in step (7).
10. Press F6 to dekey; then, press F8 to program the
value.
11. This completes TX compensation adjustment proce-
dure. Press F10 twice to return to the "SERVICE"
menu and adjust deviation per paragraph IV.
B. Method 2
This method for setting TX compensation can be
used if a modulation analyzer or meter, as described in
method 1, is not available. This method requires the
radio to be disassembled so that the RF board is
exposed, and test point TP603 on that board can be
accessed with an ac millivoltmeter. (J601 pin 2 may be
used instead of TP603.)
1. Connect dc power to the radio and switch radio
power on.
2. At the PC's "MAIN MENU" prompt, press F2 to
select "SERVICE."
3. At the "SERVICE" menu, press F4 to select
"ADVANCED ALIGNMENT."
4. At the "ADVANCED ALIGNMENT" menu, press F3
to select the TX Compensation screen.
5. At the TX Compensation screen, press F6 to key
the radio with a 67Hz tone modulation.
By pressing F6, "PTT 67Hz," you place the radio into
test mode 1, causing it to transmit on 896.0125
MHz. Microphone PTT should not be used during
this procedure, as it will cause the radio to transmit
on the mode presently displayed on the control head,
and will not generate the necessary tone.
When measuring the voltage on TP603 with the ac
millivoltmeter, keep the ground leads as short as possi-
ble to keep noise to a minimum level.
6. Use the up and down arrow keys to adjust the com-
pensation value for a null ac voltage at TP603.
7. Press F6 to dekey; then, press F8 to program the
value.
8. This completes TX compensation adjustment
procedure. Press F10 twice to return to the "SER-
VICE" menu and
paragraph IV. TRANSMIT DEVIATION ALIGN-
MENT PROCEDURE.
NOTE
adjust deviation per
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