Tim Wescott wrote in message ...
P. Venkman wrote:

SNIP

Is it as simple as finding a filter that passes 72 MHz along and
splicing it in to the wire going to the antenna? Is that likely to
cause other problems (transmitting on the wrong frequency, overheating
the RF module due to impedance mismatch, sudden death)? Assuming I
can't find a filter that passes along precisely the frequency I want,
is it OK to put filters in series (like a high-pass plus a low-pass)?
And finally, am I just totally missing the boat here with this idea?
I'm open to other suggestions.

First, you can really mess things up by playing the filter game, so
don't do it unless you need to.

Second, it may be that the transmitter has a weaker signal, or that it
is a bit off frequency. Since your average military base has about a
gazillion different transmitters it's likely that there is some spur
being generated at 72MHz, or a valid signal at your RX's image
frequency. If your transmitter is a bit weak than such a signal from
the base would have an easy time getting into your RX.

If you can get the receiver out of the plane (or if you can get to the
antenna) do a range check with the RX antenna rolled up but with the TX
antenna extended. I'd do this at some _other_ flying site. Check the
range with the suspect TX and with a known good one. If it's
significantly lower with the suspect TX then you can do all the
filtering in the world and it won't help you -- but having the new TX
fixed (or selling it and getting another brand) may help a lot.

When I first had the problem I sent the transmitter back for service -
they didn't find anything wrong, but tuned it anyway and sent it back.
The problem still existed, so I got them to replace the transmitter.
Still the same problem.

At other flying sites the new transmitter actually range checks better
than the old transmitter when checked against multiple different
receivers. For these two reasons I don't think it's that this TX has
a weaker or off-frequency signal.

Lots of other people fly at the same location with a variety of
equipement with no trouble. I've flown a variety of different gliders
there with my old transmitter and never had a problem. I really don't
think there's a conflicting 72 MHz signal.

It really is just this transmitter at this particular site - other
transmitters at the same site are fine, and this transmitter at other
sites is just fine.

Is there any way to make this work?