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November 17th 05, 12:23 PM posted to rec.radio.shortwave

wrote:
Aren't the whips just E-field sensitive? That is why they are noisy.
I'm not sure a better FET can get around a fundamental problem like
that.
+++++++++++++++++++
It all depends...in most cases a horizontal is the better choice. But
in some
locations you can use an short, active antenna as a better choice
because
you can move the smaller antenna around to sniff out the least noisy
spot.
An example, here at work we have gobs of class A computer devices.
Servers, process controllers etc. RF hell so to speak.

We need an backup time retrieval system. We use GPS, but during a big
ice
storm 3 years ago the 1" of ice killed it. Had we lost our T1 we would
have
been in deep trouble. We have some experiments that have to be time
stamped.
So I pitched the idea of a WWVB and or WWV backup system. We tried a
10'
through 60' wire antenna at several locations on the roof. But there
was just too much
noise. Then I brought in my AmRad antenna and found several locations
that were
quite enough for a WWV decoder to lock to the ~BCD signal WWV sends.
WWVB
was a washout as we have a strong, out of house, spur smack dab on top
of 60KHz.
I did have to take "extreme" precautions to keep RF from creeping up
the braid and
getting into the antenna by that patch. Lots of feritte torroids on the
coax. We went
with a homebrew version very similar to one shown in Radio Electronics
with a hefty
FET. No IM, yet. I have a "feed" from the receiver brought out at my
bench so I can
keep an ear on the audio. I also have a dedicated PC to look at the
"time" as shown
by GPS, NIST via the web, and WWV.

I have several friends who live in restrictive residential areas that
do not allow
out side antennas. In such situations it is easier to hide an short
E-field active
antenna then any sort of "long" wire.

For ~99% of SWL applications I suspect a good wire antena is the better
choice.
A wire antenna is always my first choice. For the same ~50$ as the
North Country antenna, the least expensive and good antenna that I know
of, I could errect a killer
wire antenna. But active antennas can do a good job and in the right
location can do
a extremely good job. The biggest problem from my personal experience
isn't normal QRN/QRM noise like static, but MW IM. All active antennas
suffer from this to some degree! The closer one is to a MW station,
especially 2 or more stations, the greater
this threat is. I suspect, but have no experience, that "in band", or
SW stations, nearby would cause even more IM issues.

Terry

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