Vectronics VEC-131K - Manual (Page 26)

VEC-131K Owner's Manual Aircraft Receiver Kit
24
This method requires a very sensitive VHF frequency counter with a short 6”
whip antenna. A suitable counter is the Optoelectronics model 3000 Universal
Handi-Counter.
With the receiver on, the counter should show a stable reading of the LO
frequency when its probe antenna is held near the body of IC U1. If it does so,
proceed with the following steps:
1. Set the tuning control fully CCW.
2. Adjust coil L4 for a counter reading of 128.7 MHz.
Setting the LO Tuning Range Using a Wide-range Scanner or 2-meter
Receiver
For the following steps you'll need a scanner capable of receiving the airband, or
an extended-coverage 2-meter FM transceiver (many amateur 2-meter radios
now include aircraft band receiver coverage).
1. Set the controls on the VEC-131K as follows: volume control, fully CCW
(counterclockwise). Tuning, fully CCW. A 9-volt battery should be
connected.
2. Place the test receiver close to the VEC-131K. It should have a small whip
antenna attached directly to its antenna connector.
3. Set the test receiver to 128.7 MHz. Set the receiver volume to a comfortable
listening level. If the receiver has a squelch control, set it so the receiver is
unsquelched.
4. Turn the VEC-131K receiver on using SW1.
5. Slowly adjust the tuning core of coil L4 until the local oscillator is heard
sweeping across 128.7 MHz on the test receiver.
6. Slowly adjust L4 in the other direction until the LO signal falls exactly on
128.7 MHz on the test receiver. This sets 118 MHz as the lowest receive
frequency on the VEC-131K.
Setting the LO Tuning Range Using Off-air Signals
Here are some general guidelines for alignment using available off-air signals.
The VEC-131K can be forced to receive strong signals in its “image tuning
range”, which is 21.4 MHz above the frequency it is tuned to. For example, if
there's a very strong signal present at 145.00 MHz, it will also produce a
response when your VEC-131K is tuned to 123.3 MHz (145.00 - 21.4 = 123.60
MHz.).