Topband: The Forbidden Frequency

[Tom Rauch]

> of AM BC suppression.  It could also be a junction of
sometype in the
> antenna system that is acting as a non linearity (diode
effect ?). I
> have had this occur where I joined disimilar metals in the
antenna
> element. In my case I had used a cheap steel crimp lug to
join the 2nd
> half of my vertical with the bottom copper pipe. When the
rains came I
> started hearing BC interference on 160. Replacing the lug
with a tinned
> copper lug solved that issue.
>
> I suppose a nearby steel wire fence or other poor
connections could
> generate enough energy to create the carrier, however the
BC stations
> would have to be fairly close, maybe less than 10 miles ?

I'm sure that can happen, but we can't discount transmitter
problems.

Most cases I see over distance are caused when one
transmitter mixes in another transmitter. Of course I am not
near stations, so I have very few problems with non-linear
devices in this area. I have heard mixes of transmitters at
distances of almost 10,000 miles, so co-located BC
transmitters can go a long way.

It is also possible for co-located SWBC transmitters to have
mixing problems on 160 and other bands. A SWBC station in N
Ga, now active at a new location in TN, have caused problems
here on 1805kHz, and another one in Memphis or Nashville
caused problems on 1855 kHz. In all cases it was a
transmitter isolation defect.

73 Tom