Noise is, by nature, made up of a wide range of frequencies, some of
which are amplitude modulated and at the same frequency as the radio is
tuned to (think lightening buzz in your AM radio). All of the filters
in the world will not keep them out of your speaker. They must be
attacked at the source, i.e., that cheap DC to DC converter (like I just
removed from my glider).

My perfectly working Becker radio started breaking squelch on all
frequencies immediately after installing the converter and went back to
its well-behaved self after removing power from the converter.

If you have not installed something new, or moved some wires, or changed
anything electronic in your glider, try turning your mobile phone off.
Besides, you'll enjoy the isolation that comes with it.

Good flying!

Dan

On 10/6/2016 3:45 AM, Bruce Hoult wrote:
On Thursday, October 6, 2016 at 3:38:05 PM UTC+13, 2G wrote:
On Wednesday, October 5, 2016 at 6:05:22 PM UTC-7, Vaughn Simon wrote:
On 10/5/2016 6:26 PM, Martin Gregorie wrote:
IIRC they were AM back in the mid 60s
Yes, but they weren't VHF then. They were in the 2 megacycle band and
required huge antennas for best range. Straight out of high school, my
first full-time job was working on those monsters.
All of this discussion of interference by out-of-band transmitters is way off topic; our aircraft radios have very good tunable bandpass RF filters that only pass thru the very specific VHF band we are listening to and reject all other bands. Otherwise we would be hearing transmissions from all sorts of transmitters, including other aircraft radios transmitting on an adjacent frequency. The place where the interference can pass thru into the receiver are not the antenna leads: it is the power leads where the RF filtering is less robust.
You can put as aggressive a choke as you want on the power leads :-)

--
Dan, 5J