[RFI] RFI In My Shack

Sat Dec 2 14:24:47 EST 2017

Thanks Mark!

As I said in another post:  OCFD with a 4:1 balun, the dipole fed with coax (RG-8x)  (No twin lead anywhere in the system.  System ground with an 8 foot copper surfaced rod, 10 feet from the amplifier.  That single ground strapping goes directly to the simplifier, and from there, each piece of strapping, goes directly to each piece of equipment used.  In this case, the exciter, and the AT2K matching system.

I was asked in a previous post, How do I know there is no RF in the Shack…Years ago, I built an RF detector that was in, I *believe* 73 magazine.  It has served me well over the years and has a done a wonderful job of detecting RF in shacks with a problem.  (You know, fillings buzzing and giving metallic tastes, strange radio stations coming in, via the fillings, you know, stuff like that!  J  )

Joe – W7RKN

From: mrk.twg at gmail.com [mailto:mrk.twg at gmail.com] On Behalf Of Matthew King - KK4CPS
Subject: Re: [RFI] RFI In My Shack

Joe - how do you know you have "next to none!" RF in the shack?

If you have an OCFD that's not got a REAL current choke (no voltage baluns or single core 4:1 baluns need apply here) then you have RF in the shack.  If you are using a "Carolina windom" with a radiating vertical feedline with a balun at the bottom, you have RF in the shack.

There's only one way to quantify it and that's with a meter. If you have a conventional OCFD, add a substantial-CMI current choke to the feedpoint and it'll probably end what common mode current is coming down into the shack. You can build those for a few dollars. Check out K9YC's publications on the matter:

audiosystemsgroup.com/RFI-Ham.pdf     audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf     audiosystemsgroup.com/CoaxChokesPPT.pdf

You can check out Steve's chart and other information at: http://www.karinya.net/g3txq/chokes/

If you have a "carolina windom" with a purposely radiating feedline (that's got common mode current all over the outside of the coax by definition) then you MIGHT be able to add a choke wherever the 4:1 balun is and choke of the current going past the balun. You may have to move the radiating vertical element further away from your shack somehow to eliminate it completely.

If you want to learn MUCH more about the OCFD antennas and their requirement for substantial choking, check out: http://www.dj0ip.de/off-center-fed-dipole/

Ethernet, even CAT6, is quite susceptible to RF ingress. Are your CAT6 cables properly terminated, with the shield correctly installed into the connectors? If not, they're not really shielded. Decent factory cables should be OK, but homemade cables are frequently lacking in this regard. Heck, even some of the Motorola "shielded" cables that we got straight from Mama-M in Schaumburg, IL when I worked at the nearby Motorola Service Center weren't properly terminated, having the shield snipped off right at the connector, rather than having the shield properly inserted and crimped into the connector. The use of CAT5 connectors on CAT6 cable will do the same thing.

I encourage you to do some reading at the above links.

Good luck with it!

73

Matt

AK4MK

On Sat, Dec 2, 2017 at 1:30 PM, Joe <w7rkn.7 at gmail.com> wrote:

I think I forgot to mention...I have **no** audio issues with the L7, only
the Henry.  Go figger!

OH, and I have very little (read: next to none!) RF in the shack.  That is
what is puzzling me!  How in the heck is the RF getting into my network and
only affecting the printer?

Joe - W7RKN

-----Original Message-----
From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Dave Cole (NK7Z)
Subject: Re: [RFI] RFI In My Shack

Hi again,

Given the old amp caused issues with your audio, and your new amp causes
issues with your network, we can assume you have some level of Common Mode,
(CM).

My first step would be to buy or build a common mode sniffer.  MFJ makes one
for around $100.00, or you can build one for around 10 bucks:

https://ham.stackexchange.com/questions/1271/how-to-detect-common-mode-curre <https://ham.stackexchange.com/questions/1271/how-to-detect-common-mode-currents-or-rf-in-the-shack> 
nts-or-rf-in-the-shack

If after testing with that you discover lots of CM, then start choking it on
the booth ends of the feed-line.

That may solve both your RFI issues; audio, and Networking.

If that does not solve things report back here with results.  The AC would
be the next thing I would look at...

73s and thanks,
Dave
NK7Z
http://www.nk7z.net

On 12/02/2017 10:07 AM, Joe wrote:
> Yes, A Windom, that is coax fed into a 4:1 balun.  Remember, I did
> *NOT* have this issue with my Henry amplifier, even at over 2000 watts
> out.  [Euro version of the amp!]
>
> Joe - W7RKN
>
> -----Original Message-----
> From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Dave Cole
> (NK7Z)
> Subject: Re: [RFI] RFI In My Shack
>
> Let me guess, you are using an Off Center fed dipole, or some sort of
> asymmetrical antenna  If not what is your transmit setup.
>
>
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
>
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