Pete Parisetti wrote:
> Initially I have used the KC2TX coax loops, with rather dismal results.
> Then, I have done exactly what Herb suggests
> (loop.jpg<http://www.chmusiq.com/ham/img/loop.jpg>),
> and was initially very pleased. Upon more careful evaluation, though, I
> found that there is no real gain in terms of s/n: the loop is a lot less
> noisy than the TX antenna (inverted L, 17 m tall), but in reality I can hear
> just as well (or as bad...)
Pete,
From your picture it appears that the feed line dress is along the
horizontal support. Correct me if I am wrong.....But this could cause
real performance deterioration. The key to getting some good
performance from the pennant could include:
* Antenna 50 ' (minimum) away from nearby antennas, towers, or power
lines.
* Support made by wood, fiberglass, or non conducting material.
* Good impedance matching 950 ohms and with a preamp to compensate
for the signal loss (powered over the cable) at or near the feed
point. (A multi turn 5K pot to maximize the null off the
termination could enhance performance by tuning in a BC station of
the back and tuning for minimum signals. When the sweet point is
found replace the pot with the fixed value when determined.
* Coax dress away from the feed point at one end to minimize pattern
distortion
* In a rotatable Pennant a double common mode rejection circuit
might work so the horizontal support could carry the drooping feed
line....but I think that taping them close together to the antenna
wire should be avoided...even with a decoupler at the support pipe.
* Common Mode Rejection near (15-20 feet away is fine) the feed
point with a double "T" coax toroid decoupling where the mult wrap
RG-6, RG59, or RG-174 (in the case of 50ohm feed) passes through
two rings with an earth ground between the two rings. This concept
is supposed to isolate some of the impact of the unbalanced feed
line near the Pennant
* Some gurus recommend a similar decoupling device near the shack
entry.....and although I have mine out near the antenna to avoid
common mode noise pickup I can't imagine that another one near the
house could hurt a bit.
Good luck with the noise....but almost every weekend I find something
on Top Band that can be improved upon by going over the options. I am
just plain tired of seeing someone spot me...with comments like "deaf"
or "alligator no ears". Like all of use hearing in QRN whether man
made or atmospheric is a real challenge.
73,
Herb Schoenbohm, KV4FZ
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160 meters is a serious band, it should be treated with respect. - TF4M
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