Re: How to deal with difficult reception in downtown Boston.

[umar@nerodia.wcrb.com]

On Fri, 9 Feb 2001, Don Saklad wrote:

> When reception is difficult the clearest part of the
> signal frequency band does not coincide with the
> frequency which produces the loudest sounds. It is
> usually toward the lowest frequency end of the band.

Loudness is a function of audio processing. With a few exceptions
commercial stations generally process harder than non-comm's, and
that's probably why the stations at the left end of the dial don't
sound as loud.

> What is the implication of that, if any, to any
> receiving antenna design to improve reception?...

Loudness is irrelevant. What is needed is a way to prevent nearby 
transmitters from overloading the front end of your receiver. One
way to do that is to move your antenna into the depths of a building
made of concrete and steel; this will reduce the level of all signals.
If the nearby signals are then too weak to overload your radio, while
the stations you want to hear are not too weak to receive, you win.

It that approach doesn't work, then you need to selectively attenuate
the overloading signals. This can be done by cutting a 1/4-wave long
piece of coax for each station you want to filter out and attaching it
to the antenna terminals of your radio in parallel with the actual
antenna. The far end of the coax pieces must be open (i.e. not shorted), 
and they must be cut precisely (the best way is to use a receiver with 
a signal strength meter and trim for a minimum while tuned to an 
offending signal). I've been able to achieve about 40 dB of suppression
using this method.

This won't work if you're trying to get a station whose dial position is
close to one of the offenders; in that case you'll need a tuneable notch
filter. 


Rob Landry
umar@nerodia.wcrb.com