Frequency Adjustment; Frequency Adjust Usb - Codan X-2 Service Manual

Adjustments 7-8
3.
4.
5.
6.
7.
8.
9.
10.

7.9 Frequency Adjustment

108-04840
All the channels are synthesised and locked to the 7304 kHz reference crystal
(Z3) oscillator. The reference crystal divided (7304 kHz ÷ 16) provides the
local oscillator to the Modulator and Demodulator in USB mode. Therefore
it is only necessary to adjust the reference frequency for all channels on USB.
An additional divided crystal oscillator (1814 kHz ÷ 4) provides the local
oscillator to the Modulator and Demodulator in LSB mode.
7.9.1

Frequency Adjust USB

To adjust the USB frequency:
1.
2.
Fit a shorting link to B-E to disable the noise limiter gate (located at
the rear of the Rx/Exciter PCB adjacent to the Antenna control
connector J401 ).
[A10]
Connect an Oscilloscope using a 10X probe to TP14
Oscilloscope to the following:
•
Timebase to 50 µs/division.
•
Channel One to 50mV/division (equals 0.5V/division with the
attenuation of the 10X probe).
•
Trigger set to auto sweep.
Adjust T5 [B7] for maximum amplitude.
Note: Only a small change in amplitude will be seen due to the low Q
of the tuned circuit.
Remove the 10X probe from TP14.
Connect a 1X probe to position A (part of N/L TP15). Set the
Oscilloscope to a sensitivity of 10 mV/division.
Adjust T6 for maximum amplitude.
[A7]
Remove the shorting link to B-E and return it to its parking position
(ground pins of Link 3 and 4).
Remove the 1X probe from position A.
Select the Transceiver Test Mode (refer to Section 7.5)
Select channel position 3 and the USB/LSB to LSB (this selects test
channel 17900 kHz USB).
X-2 Technical Service Manual
. Set the
[B7]
Publication No: 15-02047