[Melb-ARDF] RE: [ARDF] Some information about Ukrainian Radios, I think...

[Jay Hennigan]

On Mon, 31 Oct 2005, bruce wrote:

> > >From what I can read (and guess having used a similar unit), the
> > "threshold detector" is the whoopie mode. The tone mode is not
> > a whoopie mode, but rather a constant tone that increases in
> > volume with the strength of the signal. The tone mode is
>
> OK a BFO, much like an 80m sniffer ? Will work with any carrier.

I don't think it's a BFO, as at 2M the drift would be intolerable.  These
are varactor-tuned superhets, not synthesized.  The tone mode I suspect
is similar to what they do at 80M for the "tone" mode.  The IF gain is
varied at an audio rate.  When a carrier is present, this results in AM
modulation of the carrier which is demodulated by an ordinary AM detector.
The stronger the carrier, the louder the tone.  The modulation depth of
the superimposed gain variation is rather high, very usable with an AM
modulated 2M signal.  I suspect it's a square wave, sounds kind of raspy.
On the 80M units, the BFO is didabled in tone mode, so you are essentially
hunting a fake AM modulated carrier on a rig with no AGC.

In the 80M version, and I suspect also in the 2M version, the gain
control also varies (in steps) the frequency of the modulation applied
in tone mode.  This gives an audible indication of the present gain
setting without looking at the unit.  Higher pitch means a stronger
signal, but not quite like a whoopie as the modulation frequency is
in four or five steps and varies only with rotation of the gain control,
not with the actual signal strength.  It's more of an audible clue of
the gain knob's position than a whoopie.

The hunter uses the loudness of the receiver-generated tone as a
measure of signal strength.  The pitch of the tone gives the hunter
feedback as to the attenuation/gain pot position.  Obviously if the
pot is set to be too numb, you won't hear the tone at all, and if
too hot you blast your ears and won't hear the level drop (or much of
anything else!)  These rigs can be painfully loud.  I've been tempted
to hang a varistor across the headphones to protect my ears.

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Jay Hennigan - CCIE #7880 - Network Administration - jay at west.net
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