More SWR fun

In article writes:
I've been having radio transmission problems on my Dittel FGS-2T off
and on since I put it in. Some people say I'm over-modulate, some say
I'm under-modulated. I've got a factory boom mike and a factory wiring
harness.

Given varying reports, one might want to find out why they vary and
what is really happening. Measurement probably beats random reports.

I finally got one of those MFJ-259B SWR analyzers to see if
it's an antenna problem. At 123.4 MHz the SWR reads 2.4. It bottoms
out at around 1.7 at 131 MHz.

Doesn't seem good. If that is really the case, I would be concerned
that the best is 1.7, and that it is so far from where you want to be.


Question: Should I worry about an SWR of 2.4?

it seems worth investigating. It could be causing RF floating around in
the aircraft, which could be coupling into the microphone input.

If so, how could I
possibly tune a built in antenna?

Depends on the antenna. What do you mean by "built-in"? Is it not on the
outside of the aircraft? It may be reacting to its environment.

Also, anyone have any experience in
fixing modulation issues in a radio?

Yes. If that is really a problem, see a good avionics shop.

Second issue.

I have a couple of magnetic mount ground station antennas. They both
show a SWR of around 2.1 at 123.4 MHz and a minimum SWR of 1.1 in the
low 130's.

Question: Should I go get longer whips for these to better tune them
for the glider freqs?

Perhaps. Some allow you to loosen the screw holding the whip and
tightening it with the whip a little longer.


Note to all of you trying to tune these kinds of antennas - Having
them magnetically mounted to a steel roof makes a huge difference in
the readings.

The ground plane is coupled through the base of the magmount. Where
the antenna is on the roof or what is around it can cause the SWR to
change.


If you have something to transmit, it might be very important that
someone hear it clearly -- a good avionics shop would be the place to go.

Alan