OUTSTANDING JOB STEVE! WELL DONE!
I reread Wes' paper and noted he said "the water kept running off of the
feedline." So instead of water, he used a "WETTING AGENT" which assured
that the wetness remained on the feedline, and I assume he wetted it on both
sides. He also stated that this would be a worst case scenario and may not
be a real life situation (or something similar to that).
In real life the water does run off of the feedline - because its windows
are open. (hi)
My guess is, that's the difference.
Once again we are closer to the truth by letting Steve "Hunt" for it! (pun
intended)
73
Rick, DJ0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Steve Hunt
Sent: Wednesday, July 31, 2013 11:07 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] OT: Openwire/Window Line and Bad Wx
I found time today to do some experimenting on this issue of how window-line
losses increase when the line gets wet.
I took 60ft of 300 Ohm window (JSC 20AWG conductors) and suspended it about
4ft above ground. At one end I terminated it with a precision 50 Ohm load;
at the other end I fed it from an OmniVI-LP100Wattmeter-tuner-balun
combination. I drove it with 50W from the radio at 28.5MHz, having adjusted
the tuner for a 50 Ohm match; then I measured the current into the 50 Ohm
load with a clip-on current meter. Next I thoroughly wetted the line using a
hand sprayer filled with water from a rain butt; the SWR at the input of the
tuner rose to 2:1. I next adjusted the tuner for a match, and noted the
change in load current under the new conditions.
There was no large change in the power delivered to the load between dry and
wet. However, at this point I realised that the changes in Zo and Vp that
had occurred on wetting the line had changed the tuner and balun load
impedances, and so it was possible that changes in the tuner and balun
losses could be masking changes in the line loss. So I looked for an
alternative method.
I used my VNA2180 to make S11 measurements at the input of the 300 Ohm line
when dry and when wet. By looking at the impedance maxima and minima it was
possible estimate the change in Zo, Vp and loss. I'm still crunching the
numbers, but here are some early results when going from dry to wet:
Zo 303.8 --> 305.4 (+0.5%)
Vp 0.796 --> 0.783 (-1.6%)
Matched Loss/100ft 0.56dB --> 0.77dB (+0.21dB)
All at 26MHz
These loss increases are much smaller than those reported by Wes Stewart and
by the various on-line calculators; they are much more in line with the ARRL
measurements.
Steve G3TXQ
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