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

[Matthew Robbins]

    Dick Arnett and I had another test day at Mt Airy Forest.  We set
up an 80m transmitter, MO5, 4 minutes on, 1 minute off, and we did
several things.

    First, I adjusted the sense antenna on Val Meyer's Ron Graham RX-4
using Dale Hunt's directions.  I was shocked!  It works from 15m out. 
There were a couple distances where the sense was ambiguous, but they
were very localized---probably to less than 10m of length.  If I was
moving it wouldn't be a problem (I think).  Both were out around 400m
and maybe 700m.  At about 900m, I had the gain at max, and I was
wondering if that was normal.  I didn't do a full alignment, and I
might try to do that, but not anytime soon.  I was shocked how easy it
was to adjust the sense, and I wasn't completely fussy.

    The one thing that I was unsure of was tuning the sense antenna to
resonance.  I was really close, and a couple was walking directly
between me and the T, and I heard a little quiver, like heterodyning
(?).  After they passed, it did it again, and I realized it wasn't
them.  I guessed that was the point of resonance, and it seemed to
work.

    To test it, Dick and I walked away to 1100m.  I chose MO5 because
of the length of the 5.  I walk along and listen to the sense on "M",
then I flip the radio 180 degrees for "O", then back 180 degrees for
"5".  That way I can walk along and be checking front and back sense
every couple steps.

    One thing I thought about was the weird layout of the RX4.  If I
owned one, I'd probably buy the same box, but then mount the ferrite
and sense antenna on the small end.  The way it is now, I hold it belt
high, and the controls just seem weird.  With the ferrite on the small
end, I think it would fit my hand better, and I'd hold it chest high. 
Would there be any problems from the additional wire between the
antenna and the PC Board?  I've heard of using the sense all the time,
but I wouldn't do it for this one unless I could have a sharper sense
peak.  I'd probably try to move the sense switch to my thumb or
forefinger, and use a momentary push switch.

    I need to mount an O-ring under the tune control.  Or something
else.  It's very sensitive, and easily knocked off frequency.  Just
generally, are there any recommended mods for the RX4?

    On the long walk, Dick was checking his German 80m receiver.  I've
forgotten the callsign, but it has an 8-inch (20cm) ferrite antenna.

    We noticed all these foreign couples driving erratically up and
down the park road, and Dick realized it was driving lessons.  Which
must be terribly frustrating---who wants to take driving lessons from
a family member?

    At the 1100m point, we both switched to our Ukrainian 80m radios. 
We walked on opposite sides of the road hoping the similar radios
wouldn't affect each other.  We used tone mode, and we sort of took
some data on the walk back.  Our radios look different.  Mine uses
1600/3200 ohm headphones.  Dick's uses 50 ohm.  I plugged my
headphones into his, and carefully adjusted the volume up.  My radio
with my headphones gives a very smooth response, but my headphones in
Dick's radio was okay at low gains, but it overloaded my headphones at
higher settings.  I don't know how his headphones worked in my radio.

    Both our radios have four tones.  We called the low gain, low
frequency "1" and the high gain, high frequency "4".   I really like
Jay Hennigan's idea that low frequencies mean the receiver is dull,
and high frequencies mean the reciever is turned up (and you're far
away).  What is "best" is subjective, but it's based on two things. 
First, acceptable volume, and second: A good range of tone that lets
you find the null easily.  Here's what I wrote down:


1100m
3 best, 4 too loud, 1 nothing.

976m
3 best, 4 perfect "on null", but too loud otherwise.
4 might be a little easier to use to find the exact null.

813m
2, 3 about equal

700m
2, 3 both good, 2 better

600m
2, 3 both good.  Noisy---might be the lack of LOS (?)
1 just audible

500m
3 too loud
2 best
1 ok-improving

375m
3 too loud (except null)
2 best
1 okay--marginal.

300m
2 best
1 good

130m
1 good
2 loud

I wrote down a few notes for Dick as well.  His were generally
different from mine:

1100m
Best at the highest setting of 3 (just below 4)

500m
3 best

300m
3 best
2 okay

130m
2 best
Dick said he liked the volume pretty high, and that might account for
the differences.  It's probably a good idea to do a test yourself
rather than use my data.

I think the lesson I'll take away is this:

If 1 is solid, you should be able to get it in a minute, so run!
If 2 is better than 3, you should run anyway, and probably get it off cycle.
(Depending on terrain and vegetation, obviously.)

If 4 is best, it's a long way away.

One thing I considered was to ignore the 1-4 tone and just mark some
small graduations on the RF gain, and use the number for a comfortable
"volume" setting.  It actually might have more information that way. 
My RF gain has some db markings on it, from 0 to 100, I think.  How
are those made?  (i.e., what equipment is used?)

I'd like to do another test with the transmitter on the other side of
a large hill or ridge or something.

I'll definitely be using tone mode for my next few events.  I think
the additional information might be easier to use than non-tone
(telegraph) mode.  I need to put some tape on my gain control and mark
it 1-4.

Matthew
AA9YH
Cincinnati, Ohio USA