RadioBanter - View Single Post

Paul Keinanen · November 3rd 06, 08:30 PM posted to rec.radio.amateur.homebrew

On 3 Nov 2006 08:00:47 -0800, wrote:

My unfortunate situation is my degenerating hearing. I
now wear hearing aids in both ears and have difficulty understanding
spoken conversation no matter what the volume level.

Sorry to hear about your hearing problem, apparently you have
problems of hearing some specific frequencies.

I don't know if this might help you, but one interesting observation
about a A1A beacon and FM receivers may be of interest.

We have a nearby microwave beacon sending out call sign and locator
using ordinary on-off keying. When receiving the signal on an FM
receiver with the squelch fully open, full quieting is achieved when
the carrier is on, but strong "FM-hiss" is audible, when there is no
signal.

After a while, it was not too hard to copy the beacon message in this
"negative-CW" format.

Since the FM-noise contains white noise, it should be detectable even
if some spot frequencies are undetectable due to selective hearing
loss.

One approach would be to run the CW signal through some kind of FM
receive, limiting the carrier, but producing white noise when no
signal is available (and you would have to learn to copy negative-CW)
or alternatively use some amplitude detector to control a noise gate,
i.e. when there is a carrier present, the white noise would get
through, with no signal, the headphones would be silent.

Just an idea.

Paul OH3LWR