Topband: Line noise filters for Topband

[Tom Rauch]

> So, what variety of AC "mains" filters are recommended for use on
> Topband?

I'm not sure that would do all that much. The filter generally needs to be
located near the noise source. For example, I had a computer over 1 mile
away bothering me...it was exciting the power line in common mode against
the telco lines as the "other half " of the connection. The line filter
worked, but ONLY when it was used in conjunction with a telco line filter
placed right at the computer. Both filters had to share a common ground!!
Each individual filter did very little, without that common ground.

A line filter in the shack would only be effective if noise was working its
way directly into the receiver or receiver system via a differential in the
power cord conductors. I wouldn't think that very likely, unless you have an
old receiver from the 50's or 60's! For example, R4C's are bad about signal
ingress from power lines because the power wiring runs right through the
middle of the receiver past all the IF stages, including the 50kHz IF. Even
the antenna jack isn't shielded from the power line connections.

In a modern radio, things are organized and shielded much better. There just
aren't any problems I have ever seen in any newer radio. In my station, I
either hear noise via the actual antenna or via antenna cables in the shack
when a shield becomes broken or poorly grounded. A better correction would
always be to fix the receiver, antenna, or cables! The exception are the
R4C's, which are almost uncorrectable even with a good filter.

This isn't saying a filter won't ever  help, just that it isn't every very
likely to do much you couldn't do much better some other way. If you have a
noise ingress problem that a filter curs, you probably should have a close
look at the rest of the system!