Topband: Phased out in Boring, Oregon
tree at kkn.net
Mon Feb 11 12:40:45 EST 2008
First off - what a signal from the RA4LW station on Saturday
Yes - the call was UA4LCH, but it was Vlad's station. I was able to have a
QSO running 100 watts.
That recording was made using my 2 element array - with a parasitic reflector.
It was working better than my EU beverage (which I found out yesterday had
a break in the middle of it - now fixed).
I used a nearby (about 5 km) wideband noise source (500 KV power lines with
lots of water on them) to do some F/B measurements of the reflector and
discovered that it as tuned too low in frequency. With a reflector about
90 feet away - it seems you want it tuned about 20 or 30 kHz below the
desired operating frequency. I initially had it tuned around 1760 kHz.
I also purchased EZNEC and found that this is also what it predicted. By
moving the resonant point up to about 1790 or 1800 - I now have much better
F/B around 1830.
I have decided to put up a second parasitic element to the west of my tower,
about 60 feet away. This should work well for both being a director and a
reflector. I am tuning it to about 1865 kHz for the director and should
see somewhere between 4-5 dbi gain - and 10-15 db F/B. As a reflector, it
should work about the same with increased F/B. I put his up yesterday with
only 8 radials and it does not yet work.
I think it needs more radials before it will be effective. With 100 watts,
I see about 900 ma of antenna current when tuned as a reflector. I see
about 1.5 amps in the other reflector (that has about 45 radials on it).
I'll be adding more radials during the week and hopefully have something
that is functional for the ARRL DX CW contest.
EZNEC is a very neat tool. It allows me to imagine various things I can do
with wires on my property and see how they will actually work. Gee - I could
put a parasitic reflector behind my 4 square on 80 meters.... what would
that do? It looks like I can even model my gamma matched tower with it.
If anyone is interested in "playing along at home" - I can send some files.
73 Tree N6TR
tree at kkn.net
More information about the Topband