Topband: South Coast British Columbia 160M Beacon
Guy Olinger K2AV
olinger at bellsouth.net
Wed Jan 5 09:21:26 PST 2011
Don't be too quick to abandon the 3/8.
>From what I have seen and heard, antennas with current max up at the
bend (away from the ground) have 50 years of persistent anecdotal
success in SKYWAVE QSO's that is NOT explained by the models, theory
or popular talk. Hams are using skywave, whereas the 1930's and 40's
heavy lifters were, quite properly for what they were attempting
(commercial AM broadcasting), focusing on GROUND wave and measurements
at the GROUND. I have Terman's texts too, but he is firmly within that
ground-wave paradigm, not at all a criticism, just a note to the
NATURE of that paradigm.
I'm using up 90 and out 110 here, and after dealing with unwanted
"leakage" back to the feedline, things improved quite a bit, perhaps
10 db, if readings in the reverse beacon network mean anything. In
the end an ISOLATION transformer at the feedpoint was required here to
keep the RF entirely on the 3/8 and the counterpoise, and off of 424
feet of ladder line out to the spot. The raised feedpoint Z
exacerbates feedline isolation issues that get muddled through at
lower feed Z's. It's a lot easier to isolate a 25 ohm antenna from a
coax shield than a 120 ohm feed Z.
"Isolation" above means NO shared wire or connection whatsoever
between primary and secondary. All the baluns I have seen have a "DC"
path from the input to output ports. Dig deep enough in the ghastly
theory of how these actually work, and you discover that their
performance depends on certain assumptions about the circumstances of
their use. Their somewhat "leaky" nature is not enough to matter in
more common use, but starts to get strange with higher Z and
NON-grounded counterpoises. Since avoiding losses in ground is the
point of a raised counterpoise, this is an issue.
Another thing, what are you using as counterpoise? Some of the common
solutions bandied about can be deceptively lossy, another trap. I
have had to specifically design a counterpoise for the application,
unable to lay down DENSE radials either buried or elevated due to the
driveway bisecting the available land. Anything less than dense,
frankly, is a net loss and there are better solutions than sparse
radials that occupy far less real estate.
Probably in the end the counterpoise is three or four more times more
able to sabotage the experiment than whether the vertical is 5/16 or
3/8. The experiment really needs the pristine counterpoise.
Then one can speculate on the question of whether, FOR SKY WAVE, the
raised current max of a 3/8 avoids some degree of loss due to ground
clutter (trees?) at lower angles, makes it a better performer than
chest high ground wave measurements would suggest.
Hang in there for a while before you bail.
On Wed, Jan 5, 2011 at 12:53 AM, Martin Mac Gregor
<macgregor at xplornet.com> wrote:
> Apologies...Indulge my OCD!!!
> Getting several night-time reports from the East Coast and solid daytime
> reports to the North as well as down into California.
> Anyone out there even further South our even perhaps a night path down
> towards the Antipodes?!
> Previously I ran a quarter wave on a similar ground plane... the 3/8 (0.375)
> seems quite/very different...guess Terman and his suggestions of 0.54 (not
> 0.625!) of a wavelength being the ideal at MF frequencies might just be
> correct and worth the effort! (I will not go there with the ground impedance
> So onwards and certainly upwards/longer!
> Thanks to everyone for their reports...never anticipated the response!
> I will run until around Friday 00.00Z and then rework antenna to Terman's
> magic number and return around month end.
> Previous message:
> "Running a temporary QRSS3 and standard CW experimental beacon on 1970 kHz
> to test a new antenna
> <1W into a new 3/8 wave inverted L antenna.
> 90' vertical and 90' horizontal.
> Location .South Pender Island BC, CN88jr
> IDing as 'VE7MM at rac.ca'
> Any reports appreciated. "
> THANKS again and best 73
> VE7MM at rac.ca
> UR RST IS ... ... ..9 QSB QSB - hw? BK
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