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Old September 21st 07, 08:43 PM posted to rec.radio.amateur.antenna
Richard Clark Richard Clark is offline
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First recorded activity by RadioBanter: Jul 2006
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Default Aerial grounding and QRM pick-up: theory & practice

On Fri, 21 Sep 2007 18:40:00 GMT, Navtex-Fan wrote:

Thanks for the clarification Richard.
So in fact the coax shield was part of the antenna?


Hi Dirk,

Yes. And that "part" of the antenna was inside your home.

Please keep in mind that the same coax shield can support TWO
currents: one on the outside and one on the inside. Even though it is
the same metallic conductor, the shape creates two circuits because RF
currents on the outside cannot penetrate to the inside (that is how it
shields). Instead, those currents on the outside travel to a common
point such as the feed and gain entrance.

Also, the reverse is true as well (when we are thinking in terms of
transmission).

Put a choke somewhere along that outside circuit, and you cut off that
current. In your case, you grounded it at both ends.

The soil here is partly clay/ partly sand. In winter it becomes quite
moist. Would that adversely affect the situation?


It has happened to me (Seattle = Rain City). The "earth" connection
you use at the AC plug is NOT a shield, instead it is a safety ground.
It is in close proximity to a lot of noisy circuits. Another noise
solution is to move your plug to a different room's socket (on a
different circuit breaker). You don't have to move the radio to
experiment with this, use an extension cord. Better yet, run off
battery and unplug everything but the antenna.

Remember these last suggestions if the noise returns with rain (or
after a rain).

73's
Richard Clark, KB7QHC