[CQ-Contest] Bandpass filter

[Tom W8JI]

> Assuming it is not just in the receive line, a bandpass filter may help 
> you keep peace with any neighbors who are on the same band and others in 
> the contest - as it will cut down on any extra "crud" your transmitter 
> produces.    It even works with "clean" transmitters.
>

A traditional bandpass filter does nothing for same-band overload or 
interference, because by definition it passes the entire band.

The exception would be crystal or other very high Q narrow bandwidth 
filters, but they are generally unsuitable for transmitting or very 
expensive. I've experimented with high-Q filters on 160 meters, to allow 
duplex operation on 160 with two radios at the same time, and it is a very 
difficult filter to build. It would be much worse for something like 40 
meters.

A bandpass filter will help clean up stuff outside of the band it is 
designed for. This can make it safer to have a receiver running on one radio 
through a bandpass (say on 40 meters with a 40 bandpass filter), while 
transmitting on another radio on a different band (say 80m or 20M).

If a transmitter needs a bandpass, it might be time for an upgrade or 
repair, or more antenna spacing. :-) Usually the receiver is the big worry.

73 Tom