Topband: Common Mode Noise: PERSONAL EXPERIENCE

[Ed Swynar]

On 5th October Bob wrote...

> Anyone ever deal with common mode noise on 160 or is that something only
for higher frequencies.
>
> I am wondering if going through the trouble of installing some common mode
filters would be worth the effort on the low bands in
> order to lower noise levels.

Hi Bob,

For what it may be worth, let me pass on a bit of info to you that I
stumbled upon here earlier just this week here, and that you just might find
to be of interest...

I have two K9AY loops at my QTH --- each fed with its own run of RG-6 coax
cable --- with the ability of four point switching from inside the shack.
Anyway, I was always curious as to any "extraneous" signal pick-up by way of
the feedlines alone to each loop (the runs are 100' long, and simply laid
atop my lawn). For want of something to do with a couple of ferrite toroid
cores that I salvaged from the picture tube deflector yoke/coil assemblies
out of some TVs here, I wound an eleven turn winding of RG-6 on each toroid,
& put appropriate connectors at the ends of each winding. I then
disconnected the loop from one of the feeders, and tuned around the AM BC
band frequencies of some powerhouse stations...

Interestingly enough --- and as expected, I guess --- I could detect the
stronger stations from before, at about the S-1 level on my Icom 751A's
meter. I then inserted one of the homebrewed "filters" ahead of the rig, &
the signals disappeared.

Note that I did not short the far end of the dis-connected coax...maybe I
should have.

In any event, it was proof enough for me that a common mode choke at the
transceiver is a worthwhile effort in minimizing any RF pick-up by way of
the feedline --- perhaps it will have the same benefit in reducing noise
pick-up as well (except for, of course, any noise coming from the actual
favoured direction of your antenna).

For the expense and effort in winding these things (absolutely minimal), I
believe it to be certainly a worthwhile exercise, AND by re-cycling a
portion of a junker TV (albeit a minute portion!), you're doing your bit to
minimize landfill...

~73~ Eddy VE3CUI - VE3XZ