Jay Maynard wrote:

On 2008-02-13, RST Engineering wrote:
"noman" wrote in message
...
Otherwise, range and clarity are fine. I just got to wondering if my
homemade antenna or cable are a problem. To do the original install,
I used an rf field strength meter and simply adjusted the antenna
length for highest reading.
That probably wasn't the cleverest way of doing it.

Maybe not the cleverest way, but it's probably good enough that it's working
fine.

I've had variable luck using that approach on other types of antennas.
It's probably a better approach than the typical SWAG.

Describe your installation a little more, but I think I can guarantee you
that it isn't the antenna.

I agree. This sounds like a front end overload problem. No antenna in the
world will fix that. (Well, at least not and still work for the intended
purpose.)

I agree - the only way his antenna is likely to fix it is by removing
it altogether (which, as you point out will not help the operation of
the radio much).

No doubt the problem is that (like Jim pointed out) the FM signal is
mixing with some other signal. The question is whether that's
happening inside the portable radio, or outside it.

If it's inside the radio, reducing the amount of broadcast FM signal
getting into the receiver's front end would help. Personally, I'd do
this by putting a T connector in line with the antenna, and plugg in a
shorted quarter-wavelength (at the offending FM frequency) chunk of
shorted coax on the extra connector. The length of the stub depends
on the coax you use, and the type of connector.

If this doesn't help it's likely that the mixing is occurring
somewhere else. If it's outside the aircraft, there's not a lot you
can do (though that would mean that almost everyone would have the
problem). If the mixing is happening in the aircraft, it'll be "more
fun" to find. Someone suggested unplugging your ELT (a possibility,
and easy enough to do - just don't schedule any crashes when doing
this). ;-) I've seen all kinds of metal structures become effective
RF mixers - so the problem could be almost anywhere in a typical
aircraft (note: I don't recommend removing metal in the process of
looking for the mixing source - you may really NEED that ELT if you do
that). ;-)

Mark Hickey