In an earlier post (see Help!! Antenna Noise), I detailed how I live on
the 9th floor (top) of an appartment block, had built a 1/4 wave
vertical antenna, using a balcony railing as the counterpoise. When
the antenna was connected to my handheld Yaesu VR-500 receiver
(scanner/comms receiver), the result was noise at 8+ S units...

Two people very kindly responded to my original post, and suggested
what I might do to find where the problem was. The antenna is picking
up noise from somewhere (not the counterpoise or the connecting coax,
they exhibit no noise when connected in isolation to the main antenna).
Neither was the problem to do with the receiver being overwhelmed by
the signal, as I drove into the countryside, setup the antenna, and the
signal was fine...

I then tried the following:

1) Connected the small helical antenna that comes with the VR-500 and
the noise
VANISHES. Good.

2) Connected a simple half metre telescopic antenna to the VR-500,
and the noise returns. Not good...

Question: The helical antenna with the VR-500 obviously has some kind
of loading coil, at the BNC plug end. So I was wondering exactly what
kind of loading/matching, would there be in this antenna, that is able
to sucessfully kill the noise that plagues me here in Brussels,
surrounded as I am by tram and train lines (assuming this is the
problem of course)?

Could I build something like this to filter the noise being picked up
by my antenna? Any ideas? Circuit diagrams?

Thanks!!

Tim