Re: [TowerTalk] P.S.: Surge supression

["Rob Atkinson, K5UJ" <k5uj@hotmail.com>]

I'm certainly no expert but I'll take a stab at this.


<The concept of "RF ground loop" does not compute for me. It seems we are 
getting audio concepts in here.>
Yes, one of the problems is RF in the audio stages causing distortion.

<The ground length as a function of frequency will be all over the place 
from band to band.>
Yes again--it's a moving target.

<It seems that the best way to keep RF out of the shack is not have it there 
in the first place.>
Ideally this would be excellent but usually only broadcasters can do this.  
Hams don't have the money to put AF stages in one room or building and have 
a separate (remote) tx site where the RF is.  Most hams use transceivers 
where everything (AF and RF) is in one (small) metal box (cabinet) on a 
table in front of the op.

<Certainly it would be difficult (impossible?) to simply send it to ground 
in most shacks. The concept of safety and RF grounds are apples and oranges. 
Am I missing something here?>

You can get circulating rf currents flowing between pieces of equipment that 
are connected with coax cable (the unwanted rf flowing on the external 
surface of the shield) in one direction and returning via the ground bus.   
I'm not exactly sure how these are instigated but I think a factor is 
nearness to the tx antenna so some or all may be induced by the field.  I 
had severe problems of this type until I took corrective measures since 
there was no way for me to get far enough away from my antennas.   symptoms 
are fuzzy tx audio, tingling on transmit on the mic or cabinets.  I was 
simply trying to say that I thought running a wire from a SPD to the shack 
ground would exacerbate this but thanks to a few responses I think it's a 
nonissue:  if like me, you have already had rf problems and dealt with them 
this should not reverse anything.  If you have not had any, this should not 
start anything.
you can break up gnd. loops by putting chokes (ferrite beads, common mode 
filters, a.k.a. 1:1 ununs) in/on your inter-equipment feedlines which help 
isolate the equipment.

Rob Atkinson
K5UJ

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