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

[Matthew Robbins]

Jay wrote:

<< 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.>>

This is another thing I never understood about my Ukrainian
radio---The 4kHz/100kHz switch.  In Brno, I did the Park-O, and it's
now clear to me that this 100kHz mode is designed for courses like
that Park-O.

The map was 1:4000, which means the area was quite small by regular
course standards.  Here's how it worked:

There were 6 transmitters on continuously about 15Khz apart. 
Different age categories had to find a specific transmitter first.  I
was using the Park-O as a testing opportunity, so I walked the whole
way, and I realized that the tone mode was able to detect the
not-tuned transmitters, but I wasn't able to figure out how to use
tone mode to find them, because I was much more interested in the
crazy direction indications I was getting.  It wasn't as bad as 2m,
because I usually knew when it was happening.  The twin nulls and the
sense peak just didn't work.

Here's an online image of part of the map.

http://www.ffco.asso.fr/philosophie%20sprint_fichiers/Image8.jpg

It's Spilberk Castle, and when I was getting the crazy signals, it was
usually because the T was on the opposite side of the castle, but not
always.  The map was made for a 2002 World Cup Sprint race, and the
quality is amazing.  Look at the green vegetation---Individual plants
are mapped.  The print quality of the map is amazing.

It sure makes a lot of sense now as a way to have a different sort of
ARDF race.  And as a radio designed for races like that.

Matthew


On Sat, 12 Feb 2005 15:57:25 -0800 (PST), Jay Hennigan <jay at west.net> wrote:
> 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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