Most small portable receivers are designed to be used with a small
antenna. When you connect a large antenna, they can be overwhelmed by
signals which are much stronger than they're designed to handle. These
can be far from the frequency you're trying to listen to, but the
overloaded receiver front end generates many signals at many
frequencies, often where you're trying to listen. I've found that when I
connect a typical scanner or HT type receiver to a decent dipole, I need
to add about 20 dB attenuation between the antenna and receiver before
the receiver-generated spurs drop to a tolerable level.

This might not be your problem, but I think the chances are good that it is.

Roy Lewallen, W7EL

wrote:
I decided to try one of the simplest of antennas, a quarter wave
vertical for 20m supported by a roach pole.

I live on the 9th (top) floor of an appartment block, with a balcony.
The balcony is surrounded by a a metal railing which I decided to use
as the counterpoise.

I have a portable communications receiver with a small helical antenna.
Obviously this gives limited performance with this antenna...

Anyway, hooked up the antenna to 50 Ohm coax and connected the other
end to the comms receiver.

Result? Noise at about 8 S units, all but drowmning out the signal.
If I remove the counterpoise, it's even worse, a howling sound. If I
short the counterpoise and vertical, the signal is actually BETTER. If
I go back to the little helical that comes with the comms receiver,
then the noise VANISHES and the signal's not bad either!!!

Question: What am I doing wrong? How can I improve the vertical
(without moving)?

Question: Are there any other antennas that would be better in this
situation (9th floor appartment)? Magnetic Loop?

Any help anyone can give would be MOST welcome!!!!


Tim