Tower talkers -
I have a question about a pennant antenna.
At my QTH in Barbados I decided to try a pennant antenna that W1UK had made
for me. I usually use an 800 foot beverage to the US and a somewhat shorter
version for EU. After 4 years of not working a single EU station in CQWW
SSB, I decided to use the pennant toward EU and forget the Beverage as it
was not worth the effort. When I put up the pennant, the SWR read 4.8:1 on
the Autek RF-1. On the other hand, it seemed to work as I did hear a few EU
stations before the contest. I did not have the time to experiment any
Instead, I decided to make a second pennant at home and bought two K1FZ
pennant transformers. In CQWW CW, I had little time so I put up two
pennants instead of either Beverage. Unfortunately, they both measured the
same high SWR on the Autek RF-1. I just used them anyway, and they seemed
to work as expected.
I decided to bring one pennant and transformer back home to figure them out
once an for all. I had many theories ranging from ground conductivity,
proximity to metal roof, or the towers themselves - all of which would be
different at home. I strung up the pennant in my back yard and once again,
the SWR measured 4.9:1. The feedpoint was antenna to K1FZ transformer to 1
foot coax to RF-1. I tried fooling with geometry of the antenna, angle of
feedline escape, etc, and very little change was noticed.
Having very little test gear at my house, I tried one last thing. I tried
to measure the impedance of the antenna itself. Somewhat clumsily I managed
to get the lugs on the ends of the antenna wire in the connector of the
RF-1. Once I removed my fingers from any of the metal surfaces, the
impedance measured 860 ohms. This is about what I should have expected.
The RF-1 does not display the reactive component and the SWR was out of
range so I could not calculate it. Assuming the antenna might be OK, I took
a 1K resistor and put it across the transformer input and measured the
output. Once again the SWR measured about 5:1. With the 18:1 transformer
ratio, I expected it to be closer to 1:1. Interestingly, a similar
experiment yielded the same results with the W1UK Balun.
I am looking for advice. My guess is the antenna is fine and the problem is
either my measurement technique or the feedpoint itself. Should I be using
a balun after the transformer? Is there some leakage or coupling path that
is fouling my measurement that I need to isolate?
Other notes, all measurements on 160 meters (80 not much different), wire is
18 gauge insulated copper.
Any suggestions are welcome
73, Tom W2SC
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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