That's a pretty interesting set of tests. Thanks!
It would have been more interesting, though, if they had duplicated the
tests without the counterpoise, and without the length of coax from the
rig to the antenna. My point all along has been that for these short
loaded whips that the counterpoise is doing most of the work. I just
want to see how MUCH of the work it's doing.
73,
Dave AB7E
On 9/25/2022 2:37 PM, SCOTT MCDONALD wrote:
Dave, if you’d like to see a reasonably controlled test of radiators,
you might want to take a look at the 2002 HF Pack Vertical Antenna
Shootout Results. The antennas range from full size to a resistor
with a short whip.
https://www.qsl.net/hfpack/antennas/shootoutvertical2002.html#vertical
For sure, the counterpoise was a resonant horizontal quarter wave, not
a drag wire, and not counterpoiseless (sic), but the results were
otherwise controlled nicely for direction using quality gear by people
fairly knowledgeable about portable and pedestrian mobile ops. If you
look at the numbers you can even (kinda) infer the radiation
resistance goes up with the square of the radiator length thing, as
one would expect.
And while there is no AX-1 tested, there is one antenna very much like
it in the mix, about the same length, same dimension loading coil,
etc. (not judging here Wayne, feel free to rebut). And it’s about 5dB
down from a full size quarter wave under controlled conditions, not a
surprising result.
About the only thing missing seems to be some practical use data (per
Julia) comparing a drag wire counterpoise as actually used in the
field with the Shootout’s single horizontal counterpoise, if someone
hasn’t already done that. Given the interest at the time I’d guess
that answer might exist in HF Pack lore too - maybe someone here knows?
Scott ka9p
Make something good happen!
On Sep 25, 2022, at 3:26 PM, David Gilbert <[email protected]> wrote:
Personally, I only care about a pure comparison test in as controlled
circumstances as possible. Any practical test like you describe will
have so many variables that it won't be useful for anything other
than as an anecdote. "Ground" is going to be wildly different
depending upon location. Propagation is highly variable for distant
reports, and if you instead use a nearby setup for reception, it will
make a difference which direction is it relative to the trailing
counterpoise.
Besides, lots of people have already proven they can make contacts
with the scenario you describe, but nobody has a clue how efficient
that might be or not be.
73,
Dave AB7E
On 9/25/2022 12:30 PM, Julia Tuttle wrote:
Hi Dave,
I think that's a proper comparison in a physics sense, but I don't
think it fully represents how the AX1 is deployed in practice.
I would run both an ideal scenario -- the one you described -- amd a
practical scenario -- something like a KX3 + internal batteries on a
picnic table, AX1 on the bipod, and the counterpoise trailing down
to and across the ground.
73,
Julie
On Sun, Sep 25, 2022, 15:19 David Gilbert <[email protected]> wrote:
To be a proper comparison, the AX1 needs to be out it the clear away
from anything else, preferable at a height that allows the
counterpoise
to be hanging straight down with the end maybe a foot or two off the
ground. Measurements should be with the AX1 at the same height above
the ground without and without the counterpoise. Ideally a KX2 or
similar rig should used, be battery powered (with very short leads if
external), no coax, and no body contact to the source of RF. Signal
reports should be in microvolts ... the number of contacts isn't
really
useful and neither is SNR if the readings are taken over a lengthy
period of time.
If I can get my hands on an AX1, I plan to either climb a tree or
set up
a tall fiberglass step ladder for the AX1 as far away line of
sight from
my home as practical. I'd use my KX2 for the signal source, using
the
Tune function to put out RF without touching the KX2. Near my home
I'd
set up the portable vertical antenna I described in an earlier
post, and
feed that to my K3 set to read microvolts. I'd operate the AX1 (with
and without counterpoise wire) and any other antenna for
comparison, and
have a friend record the microvolts from the K3 as a blind test.
I would use the tuner in the KX2 to simulate actual use, but that
would
of course introduce a variable for possibly different amounts of
loss in
the tuner depending upon the load. I don't see a good way to
avoid that.
73,
Dave AB7E
On 9/25/2022 7:06 AM, Ron Gruner wrote:
> I've just run two tests of my WSPR/AX-1 set-up with and without a
> counterpoise. Each test ran 24 hours over the last couple of
days. Here are
> the results:
>
> COUNTERPOISE?
> YES NO
> ------- -------
> Total Contacts 152 129
> Maximum Distance (km) 15,720 17,276
> Median Distance 2,137 1,823
> Median SpotQ 446 398
>
> Where SpotQ = Kilometers / [(2 Watts x (SNR in DB + 36))/36) ]
>
> The WSPR circuit's ground and SMA connectors are apparently
providing
> enough of a counterpoise to propagate a respectable signal.
>
> Here's a close-up of the rig with no counterpoise:
> https://gruner.com/k4rhg/wspr_ax-1_nocounterpoise.png
>
> 73,
> Ron Gruner
> K4RHG
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