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

[Matthew Robbins]

I spent a couple of hours in Mt. Airy Park today.  I put up a single
80m transmitter with a 4 minute on --- 1 minute off cycle.  (I choose
the 4-1 for no good reason.)  I put it up about 700m more-or-less down
a road, since the ground was a little mushy.

I was testing two things.  

First, I was adjusting the sense antenna on a Ron Graham receiver that
had absolutely no fore-aft directivity.  I sat down at a picnic table
in the sun, since it was just a beautiful day out, and followed the
directions.  I was able to get a really nice sense adjustment made at
least for 700m.  Then the acid test:  I walked 700m to the transmitter
checking the receiver every couple steps.  Around 300m from the T, I
couldn't detect a difference between front and back.  It went on for
about 100m, so I decided to stop and adjust it there, and see what
happened.  So what happened?  Mostly disappointment.

I didn't follow the directions exactly.  They say to place a metal
shield over the part of the sense antenna inside the case when the
metal case cover is off.  I didn't take anything with me, so I just
did without.  I noticed holes that are drilled in the cover for this
adjustment, but they're covered by a label and a piece of clear
plastic.  I've decided to open up the holes because the adjustment
(which I plan to continue experimenting with) seems like it's going to
take a while, and require lots of trial and error.

I was hoping someone knows or could explain some way to do this
adjustment with measuring equipment.  Are there measureable quantities
here?  I don't need "the answer" as far as what number to set the
quantities to, because I don't mind making up a matrix of values and
testing them---Although I'll have to think about ways to mitigate the
700m walk to check it at different distances.

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.

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.

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.  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.)

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.

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.

Matthew
AA9YH
Cincinnati, Ohio USA