Re: RFI in audio chain

[Jan Ditzian]

This is a wrap-up post to the discussion about RFI feedback into the
audio of my K3.

First, I want to thank everyone who offered suggestions, most of which I
tried to follow up.

After numerous failures, I managed to lure a local guru--a ham who makes
his living getting RF and audio things to work.  After ten minutes of BS
in my ham shack, he said to start disconnecting each wire from the back
of the K3, one-by-one.  Some of you may have told me to do the same
thing, and I remember approximating that, but somehow I must have messed
up.  At any rate, as soon as we disconnected the line from my outboard
USB sound card to the rear input of K3, used for digital work, the audio
RFI went away.  My friend says he thinks that an isolated line would be
better, but the fact that I have a stereo output going directly to the
mono input is probably the real culprit.  At the moment, only hours
since his discovery, I have successfully worked on 80 and 40 meters with
the amplifier, but I have not yet fixed up an isolated digital line.

My thanks to the entire K3 community who attacked this problem.

I am now using the original vertical, fed with patched lengths of
hardline, with a hardline, wound choke at both ends.  Each choke is
40-50 feet long.

I also discovered that my RF ground point in the shack (back of the
Ten-Tec KW tuner), shows 30-50 ohms resistance vis-a-vis the electrical
ground terminals in the shack.  Another rod as part of my RF ground
system may be forthcoming.

73,

Jan, KX2A

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[Don Wilhelm-4]

Jan,

That 30-50 ohms resistance may be a shack safety problem.  Your shack
ground rod must be connected to the Utility ground rod by a heavy
conductor (#6 minimum, but #4 preferred).

That ground is only for AC safety and some part of lightning protection.
It does not present an effective RF Ground.  To use an example, consider
an 8 foot connection to that ground and think of a 10 meter signal.  
That 8 foot connection is about 1/4 wavelength, so while the impedance
at the ground rod may be low, the impedance to 28 MHz RF at the shack
end is quite high (due to the properties of antennas and transmission
lines).  In other words, what you are viewing as an 'RF ground' at 10
meters is instead exactly the opposite, it is a high impedance to RF at
10 meters.

The proper place to solve RF problems is in the antenna field, and not
by attempts (sometimes futile) to bond things to a driven ground stake.

73,
Don W3FPR

On 12/22/2015 8:40 PM, Jan Ditzian wrote:
>
>
> I also discovered that my RF ground point in the shack (back of the
> Ten-Tec KW tuner), shows 30-50 ohms resistance vis-a-vis the
> electrical ground terminals in the shack.  Another rod as part of my
> RF ground system may be forthcoming.
>

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[Jim Brown-10]

On Tue,12/22/2015 5:57 PM, Don Wilhelm wrote:
> That 30-50 ohms resistance may be a shack safety problem.  Your shack
> ground rod must be connected to the Utility ground rod by a heavy
> conductor (#6 minimum, but #4 preferred).

Yes. I will again strongly urge Jan to STUDY my tutorial on Power,
Grounding, and Bonding for ham radio.
http://k9yc.com/GroundingAndAudio.pdf  If equipment in the shack was
properly bonded, removing that audio cable would not have solved the
problem (and there would have been no problem).

73, Jim K9YC


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[EUGENE GABRY]

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Jim
Brown
Sent: Tuesday, December 22, 2015 10:33 PM
To: [hidden email]
Subject: Re: [Elecraft] RFI in audio chain
>Yes. I will again strongly urge Jan to STUDY my tutorial on Power,
Grounding, and Bonding for ham radio.
> http://k9yc.com/GroundingAndAudio.pdf  If equipment in the shack was
properly bonded, removing that audio cable would not have solved the problem
(and >there would have been no problem).

73, Jim K9YC

Good study material for all to absorb! I would only add one additional
to-do. Check all your bonds, especially outside ground bonds, annually. Even
though you did a good job of bonding connections, oxygen oxidizes, in time.
Speaking from experience :)

73 Gene, N9TF
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