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Danny Richardson · July 30th 07, 11:39 PM posted to rec.radio.amateur.antenna

On Mon, 30 Jul 2007 13:10:36 -0700, wrote:

Sounds like that particular antenna system is not very well decoupled
if you are having noise ingress problems of that level.
I have a 21 inch CRT sitting right next to my ungrounded radio and
have no noise problems at all.

Not all common mode problems can be fixed by transmission line/antenna
decoupling. Noise can be coupled to the transmission line or other
station equipment (as in my example). It would have made no difference
had I the world's best decoupling choke installed at the transmission
line to antenna transition point the noise would still be there.

Secondly I have never been able to find any broadband balun or choke
(80-10 meters) that is effective on all bands. Indeed, I have measured
the common mode impedance of some commercially made broadband baluns
that have had as little as 100 ohms on some bands while very high on
others. Common mode current will always be with you the only questions
are what is the source and how much. It may be very little and no
consequence while on other bands - particularly in a multi-band
antenna system - it can be substantial.

I have no doubt that your CRT monitor didn't give you any problems
but, then again you weren't using mine. So you are not comparing
apples to apples.

Additionally, you can also have common mode problems via electrical
wiring system. And no matter what you do to decouple the antenna will
have any effect on that but, utilizing a good ground could reduce it
substantially, although, additional filter may be required.

It boils down that a good single point station RF ground system can't
hurt - it can only help. It just an additional protective measure. One
I would not be without.

Danny, K6MHE

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