Alignment - Method 2; 455 Khz If And N/L Alignment - Codan X-2 Service Manual

X-2 Technical Service Manual
7.7.2

Alignment - Method 2

The following steps detail the alignment procedure using a Spectrum Analyser
and Tracking Generator:
1.
2.
3.
4.
5.
6.
7.
8.

7.8 455 kHz IF and N/L Alignment

108-04840
There are two tuned transformers in the 455 kHz IF circuit located on the
Rx/Exciter & Control PCB:
•
•
The alignment may be carried out either in the Test Mode or normal
operating mode.
To align the two transformers:
1.
2.
Publication No: 15-02047
Select the Transceiver Test Mode (refer to Section 7.5).
Select channel position 11 and the USB/LSB to LSB.
Remove the shorting link parked on the two ground pins of Link 3 and
4 [D5] and fit link to B-E of N/L TP15. This will open the noise limiter
gate.
Connect the Tracking Generator set to an output of 7 mV RMS
(-30 dBm) direct to the receiver input (P1 pin 1 and ground pin 2) on
the Rx/Exciter & Control PCB. This will by-pass the Broadcast Filter.
Connect the Spectrum Analyser input to TP14
permitted). Set up the Spectrum Analyser as follows:
•
Centre frequency to 455 kHz.
•
Frequency span to 100 kHz (10 kHz/Div).
•
Reference set to 10 dB per division.
Adjust the Spectrum Analyser sensitivity to about -50 dBm to display
the frequency response of the 45 MHz roofing filter.
Adjust transformers T3
ripple over 15 kHz span centred at 455 kHz. If desired, the reference
level can be changed to 2 dB per division to improve resolution.
Note: In this Test mode VCO1 and VCO2 are set to 44.544 MHz
enabling the receive frequency to equal the 455 kHz IF
frequency. This allows the Spectrum Analyser and Tracking
Generator to be used to align the roofing filter at 455 kHz.
Remove the shorting link to B-E and return it to its parking position
(ground pins of Link 3 and 4).
T5 in the IF path to the Sideband Filter.
T6 is located at the output of the noise limiter 455 kHz amplifier.
Select any receive channel.
Connect a Signal Generator set to 1 kHz above the selected channel
frequency (1 kHz below for LSB) at an output of about 10 mV EMF
to the receiver input.
and T4 and inductor L10 for less than 2 dB
[B5]
Adjustments 7-7
(50 Ω input is
[B7]