[ARDF] 80m Testing in the Park...

[Jay Hennigan]

On Sat, 12 Feb 2005, Matthew Robbins wrote:

> Second, I was trying to figure out the tone mode on my Ukrainian 80m
> radio.  Long story short: I'm confused.  I thought there were 3 tone
> levels, but there are four.  My first thought was to set it just
> touching the maximum tone about 50m from the T, and then walk away and
> record when the tone dropped to the 3rd, 2nd, and 1st level.  Well, it
> didn't.  It didn't drop to a lower tone, but as I would swing it
> around I could hear the tone change strength.  I should've thought
> about it more out at the park so I could describe it better, but when
> you set the gain in tone mode, there is a tone even when the T is off
> (responding to noise?), and then some mixing or additional modulation
> of the tone to give you a way to descriminate direction.

The tone mode doesn't change tone frequency with signal strength.
The frequency of the tone is stepped with the setting of the gain
control, as an audible indication of where the gain control is set.
The loudness of the tone, just as the loudness of the BFO-recovered
audio, varies with signal strength (and with the setting of the gain
control.)

> When I was set at the high tone, and walking away from the T, it was
> *really* loud.  And that made me think the purpose of the high tone
> wasn't for near the transmitter.  I ran out of time before I could
> make another test walk, but I think the four tones are completely
> independent of the transmitter signal.  They are completely controlled
> by the gain control.  So when you're far away, the high tone somehow
> mixes with the transmitter signal and gives you a decent range of
> response to let you find the T.  As you get closer, the mixed tone
> signal becomes less and less discriminatory, meaning you can't tell
> which direction it is anymore, and you need to reduce the gain to a
> lower tone (same as a smaller gain) so you can get back a usable range
> of tones.

Precisely.  Low tone = low gain = numb rx = close to T.  The dynamic
range of the Ukranian sets is amazing.  I can get a null a couple of
feet from the antenna or several miles away.

> I'm hoping to try to find a way to mark the gain control to hopefully
> give some sense of the distance to the T.

I used some 3M color-coding tape.  Example here:

http://www.west.net/~jay/images/80mdial.jpg
http://www.west.net/~jay/images/80mdial1.jpg

> The biggest thing I learned
> today was that you need to pay attention to the tone response as you
> rotate the radio and possibly adjust the gain up or down to find the
> most discriminating setting.  (When you're using the tone mode.)

The tone mode essentially modulates the receiver IF gain with a tone
that varies in frequency in steps depending on the gain control.  This
can be useful as a quick audio indication of overall signal strength
such as "Still very audible on lowest gain(tone)".   It is most useful
in wideband mode as the tone is still very usable when the beat between
the received signal and the BFO is outside of the audible range.  In
congested conditions or when a homing beacon is on a different frequency
this can cause confusion, of course.  In wideband mode, the tone mode
is really the only way to DF a signal that isn't accurately tuned, as
you can't hear it otherwise.

> Also, I found out that in Tone Mode, the sense button is not
> automatically on.  You do have to push it in tone mode or you get a
> double null pattern.   I think everyone knew that but me.  (To
> understand why that is, it's because I really didn't understand what
> tone mode was, and when I discovered it, during a race, I didn't have
> time to test it and to think it through.  A couple of wrist-twists,
> and it sure seemed like the sense was on.)  Yeah, I know it's a bad
> thing to try new stuff in competition, but I did.  Luckily, it never
> got me in trouble.

The sense on/off is independent of tone mode.

> I'm still not 100% sure of tone mode.  I think that now that I know
> about the need to set the gain carefully, it might be superior to the
> telegraph mode.  It's pretty amazing to me that I didn't know about
> the sense.  In the past, I've always used it for very close to the
> control, and since I thought the sense was on, I just moved my wrist
> enough each way to detect a falling off of the signal.   Now that I
> know about the sharp nulls still being there, I'm definitely going to
> try it.

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