Posted by
Solosko, Robert B (Bob) on
Jan 24, 2007; 7:52pm
URL: http://elecraft.85.s1.nabble.com/Rf-in-the-shack-distorting-audio-tp443216p443223.html
Thanks for all of the very good information and suggestions. My
counterpoise had been several wires running together - I wasn't aware of
the need to separate the ends. So, I removed the counterpoise that I had
and made 3 new separate ones, 1/4 wave for 15, 17 & 20 meters, cut for
the middle of the phone band on each. These are attached to the
grounding screw on my KAT100 and run in 3 different directions... and
guess what? The problem is still there. Measuring with my field strength
meter, there appears to be no appreciable difference in the level of RF
in the shack on these bands.
On to the next things to try, which will have to wait until the weekend
when I can hang out of my window during daylight. The next things I'll
try are 1) attach the counterpoises directly to the coax ground on the
balun, 2) replace the 9:1 voltage balun with a 4:1/1:1 current balun, 3)
running more, and different lengths of wire from the KAT100 to the
ground rod (although if the counterpoises have little affect, would this
have any different affect?) 4) changing the length of ladder line to the
balun and the length of coax from the balun to the KAT100 (I don't have
a lot of room for flexibility here). I'll let you know the results.
Thanks again for all of the information and suggestion.
Bob W1SRB
-----Original Message-----
From:
[hidden email]
[mailto:
[hidden email]] On Behalf Of Solosko, Robert B
(Bob)
Sent: Monday, January 22, 2007 12:57 PM
To:
[hidden email]
Subject: [Elecraft] Rf in the shack distorting audio
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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