[Elecraft] Artificial RF Ground

[Ron D'Eau Claire]

Don is right. It's quite possible that your shield *exterior* is acting as
another radial and, if the run to your shack is near 1/4 wave or 3/4 wave,
you have a high impedance at your rig. The solution is to decouple the
shield with a toroid or other device near the 1/4 wave point. 

As Don suggested, at the entrance to the shack is a good point. Otherwise, a
point 1/4 wave from the radial is ideal. 

Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Don Wilhelm
Sent: Thursday, April 02, 2009 5:47 PM
To: ng3v at comcast.net
Cc: Elecraft at mailman.qth.net
Subject: Re: [Elecraft] Artificial RF Ground

Tom,

The only possible troublesome item that you have talked about is the 
"feedline laying on the ground".  That could be picking up radiation 
from the vertical and bringing it into the shack - that would be from 
'common mode' current being induced on the coax shield.  Burying the 
coax may help.  Many such problems can be tamed with a balun at the base 
of the antenna, plus a current choke about a half wavelength away (or at 
the entry to the building).  Normally, only the balun at the antenna is 
sufficient, but in your case, it may be that the shield of the feedline 
is picking up radiation from the antenna itself and carrying it into the 
shack - thus my recommendation for a current choke at the entry point.  
A ferrite choke will produce the best results, but if you have excess 
coax length, try coiling the coax into an inductor - 6 to 8 turns about 
6 inches in diameter at the shack entry point may help tremendously.

If you must resort to the use of an artificial ground, I recommend that 
it be attached to the coax shield at the point where the coax enters the 
house - in other words, get rid of the common mode RF before it gets 
into the shack.

OTOH, if your feedline is not coax, other means may be necessary.  One 
could try various incantations while waving chicken carcasses about - it 
may not help, but it can make one feel better about it.

No number of ground rods will fix the problem.  RF feedback is best 
handled at the antenna. or at other select places in the antenna 
system.  The exact location depends on your installation, there are no 
general answers that will work in every situation.  RF moves in ways 
that appear to be mysterious until one realizes that *anything* (even a 
ground rod) can become a part of the antenna system - and then one can 
move forward to control where the RF currents will flow.

73,
Don W3FPR

NG3V wrote:
> Good Evening Group,
>
> Anyway, my shack is in an enclosed room in the basement with no direct
> access to the outside world.  My antenna is a ground-mounted vertical
about
> 15 feet from the house with buried radials.  The feedline is laying on the
> ground.  Poor arrangement, but best I can do for the time being.
>
>   
>
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