Thanks, yes I agree that it is important to be as correct as we can. Still,
I have confidence in our observations.
The dry / wet response was a puzzle at first, but my rationale is
straightforward. On the dry ground the fields on one side are almost
entirely in the lossy dirt -- not to surprising that there would be a lot of
loss. I would expect somewhat similar results (easy to check, but we didn't)
if the line were tacked to lumber or something similar. I hold mine off the
house with 3 inch TV twinlead type standoffs.
The other extreme, at its limit, I would think would be having the line
laying on a copper or aluminum strip. Now we have the straightforward case
of parallel strip lines. Yes the impedance will be different -- important in
a matched system, but we adjusted for mismatch since we were interested in
loss (in most amateur applications, the system is adjusted for match at the
sending end). The loss in the parallel stripline should be about the same as
the window line. I think the wet grass was acting more like a conductor than
a lossy dielectric, and thus more like the double strip line. At least that
was the only explanation that made sense to me.
I was surprised at that result as well, so we repeated it several times with
consistent results. The moral of the story--in a temp situation (Field Day,
for example) don't run window line on the ground!
Regards, Joel Hallas, W1ZR
From: email@example.com [mailto:firstname.lastname@example.org]
On Behalf Of Steve Hunt
Sent: Friday, January 27, 2012 8:11 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Re. [Ten Tec] Grounds and balanced fed verticals
Nice to hear from you!
The ladderline loss figures quoted in the Antenna Book - which I believe
are also repeated in TLW - are out by a factor 2. It's very easy to
demonstrate that with a simple I^2R loss calculation. I'm happy to show
the sums if you need convincing.
Tenths of a dB differences may not matter of themselves. However, they
*do* matter when the losses you are trying to measure are of the same
order. In your article you said that the measurements on dry line agreed
with TLW predictions "within a few tenths of a dB in each case". Given
that the TLW loss figure for ladderline is 0.05dB at 3.7Mhz, measuring
something "within a few tenths of a dB" of that figure could represent a
Also, we need to remember that in many (if not most) Ham applications
ladderline is operating at a high VSWR, so what might seem to be
negligible differences in *matched* loss figures become much more
significant in real life applications.
I think the most puzzling result you reported was the substantial
increase in loss (3dB to 10dB) when you set the line on dry ground,
whereas there was virtually no increase in loss when you set the line on
wet ground. When (or is it if) our UK weather improves, I intend to try
some measurements myself.
On 27/01/2012 02:44, Joel Hallas wrote:
> Well, I'm not sure if TLW is exactly on or not, but I'm pretty comfortable
> with our technique. When we're talking differences of 0.1 dB, not sure if
> the exact value is too critical for the usual HF amateur.
> Bob and I took careful data, rematched with every new set of data to
> compensate for any Zo differences and used good, commercially calibrated
> gear to take the data.
> Regards, Joel Hallas, W1ZR, BSEE, MSEE
> Westport, CT
TenTec mailing list
TenTec mailing list