[Elecraft] Rf in the shack distorting audio

[David A. Belsley]

Robert:
   This problem is easily fixed.  Add a counterpoise for each band on  
which you operate.  The counterpoise is simply a 1/4 wave length of  
wire for the particular band.  Attach one end of the wire to your  
K2's ground, run the wire as inconspicuously as possible, keeping it  
out of reach of animals, children, etc.  Be sure the far end, which  
can have quite high rf voltages, is well insulated -- and the more  
isolated from other electronic items the better.  If you operate  
multibands, you may run your separate counterpoises together over  
part of their stretch, but separate the last several feet of each  
from the others, and insulate well.

best wishes,

david belsley, w1euy

On Jan 22, 2007, at 12:56 PM, Solosko, Robert B (Bob) wrote:

> Hello All,
>
> 	Several month ago, after I finished my KPA100, I found that when
> transmitting SSB on the higher bands (20, 17 & 15), the computer
> speakers across the room, when turned on, would screech - adjusting  
> the
> speaker volume had no effect (but turning off the speakers quieted
> them).  During a QSO a few weeks ago, it was commented that it sounded
> like I was getting RF into my audio.
>
> 	To make a short story long, I don't have a very good ground
> system, so there's a high level of RF in the shack - the shack is  
> on the
> 2nd floor, about 18 ft above the ground rod. My primary antenna is  
> a 100
> ft multiband horizontal dipole feed with ladder line into a 9:1 balun,
> which is connected to my KAT100 via 6' of RG8. While the antenna works
> great on all bands (the KAT100 has no trouble tuning it), there's a
> fairly high SWR on the feedline on the higher bands. I have two
> different length wires connected the ground rod to the KAT100, and
> adding counterpoises for 20, 17 & 15 meters hasn't change the high  
> level
> of RF in the shack on these bands.
>
> 	A week or two ago, I put up a second antenna, a vertical
> parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna  
> has
> very low SWR on these bands. When using this antenna, I have no  
> problems
> with the computer speakers screeching, so there's apparently not  
> much RF
> in the shack. This weekend, during the NA QSO party, when using the
> ladder line fed dipole on the higher bands, several times, I was told
> that my audio was distorted, and switching to the vertical coax fed
> dipole immediately cured the problem.
>
> 	So, the question is, what can be done to fix the distorted audio
> when there a high level of RF in the shack (besides getting a better
> ground system - I plan to put in one or two more ground rods, but I
> won't be able to do that until after the ground defrosts in the  
> spring).
> The mic I'm using is a RadioShack Electret replacement element in  
> an old
> mobile mic case - the case is plastic and not shielded, but the  
> cable is
> shielded, and I have grounded the mike jack in my K2.
>
> 	All suggestions about how I can eliminate the distortion will be
> greatly welcomed,  as well as suggestions about how I can reduce the
> high level of RF in the shack besides adding more ground rods.
>
> 	Thanks
>
> Bob W1SRB
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--------------------------------------------
david a belsley
professor of economics
boston college