Vectronics VEC-131K - Manual (Page 27)

VEC-131K Owner's Manual Aircraft Receiver Kit
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If you (or a friend) have a ham license and a two-meter transceiver, you can use
the 2-meter transmitter to align your radio. To do this, transmit a signal (using
the transceiver's lowest power setting) on 147 MHz. This corresponds to 125.6
MHz, which is the approximate mid-point of the VEC-131K's tuning range. Set
your radio's frequency control to the 12:00 (or mid-band) position, and tune L4
until you hear the 2-meter radio's signal.
Lacking any other means, simply set coil L4 so its slug is level with the coil top.
You should be able to copy air traffic with this setting. In time, with some
monitoring experience and familiarity with air traffic activity, you may be able to
find a better setting.
A scanner guide will tell you what your local airport frequencies are, and this
may help you find a known channel to "key" in on. Also, aircraft VOR beacons
operate below 118 MHz. If you set L1 so these fall just out of tuning range at
the low end of the dial, you'll be "in the ballpark".
RF Stage Alignment
RF stage alignment involves “peaking” coils L2 and L3 for best receiver
sensitivity. “Peaking” the coils involves spreading or compressing the coil turns
while listening for an improvement of a very weak signal. In general, if the coils
were wound as directed in the assembly instructions, the receiver RF tuning is
probably very close as it is. For those who wish to optimize the tuning the
following procedures should be followed.
Set the signal generator as follows:
•
Frequency.................................127.0 MHz
•
Modulation ...............................1000 Hz, at 30% AM
•
RF Level...................................5 uV
1. Connect the signal generator RF output to the VEC-131K antenna connector.
2. Turn the VEC-131K on, and set the volume control to a comfortable level.
3. Carefully tune the VEC-131K until the signal generator signal is heard.
4. Adjust the signal generator level until the 1000-Hz tone is barely heard above
the background noise.
5. Use a toothpick or insulated plastic tuning tool to carefully compress or
expand the coil windings of L2 and L3, while listening for the point where
each coil “peaks” to give the loudest 1000-Hz tone in the receiver speaker.
Image Rejection
The VEC-131K has two stages of airband "pre-selection" to keep out-of-band
signals from getting into your radio. However, nearby 2-meter amateur activity