Thanks Jim
I’ve done what you suggested. My reason for asking was more about a friend
of mine who swears that it’s the easiest test. The test I described was
intended to be done at the back of the radio. I’m currently in FL so I’m
going to try it when I get home later this week.
*Best 73 de WA2SQQElmwood Park, NJ"The only dumb questions are those we
don't ask"*
On Tue, Jan 21, 2025 at 12:21 PM <rfi-request@contesting.com> wrote:
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> Today's Topics:
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> 1. Question about common mode noise (Bob WA2SQQ)
> 2. Re: Question about common mode noise (Jim Brown)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 20 Jan 2025 22:09:39 -0500
> From: Bob WA2SQQ <wa2sqq@gmail.com>
> To: rfi <rfi@contesting.com>
> Subject: [RFI] Question about common mode noise
> Message-ID:
> <
> CAK47ybnPWbsaXQGgc0KiGB+mW6OaZDMzHgiBQcqP92cxr2tCyA@mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> I?m
> I?m seeing what appears to be wide band possibly common mode noise on 160
> thru 40m.
> A friend of mine suggested
> 1 Dosconnect the antenna to verify no noise and no S meter indication.
> 2 Connect the antenna and tune to a portion of each band with no signals
> 3 Partially disconnect the antenna leaving only the center of the pl259
> connected.
> 4 Compare the noise with shield of coax connected and disconnected.
>
> He swears that if the noise increases when the shield is connected, that?s
> a positive indication you have an abundance of common mode noise.
>
> I?m not so sure this is a valid test. Comments?
>
>
>
>
>
> *Best 73 de WA2SQQElmwood Park, NJ"The only dumb questions are those we
> don't ask"*
>
>
> ------------------------------
>
> Message: 2
> Date: Mon, 20 Jan 2025 21:43:46 -0800
> From: Jim Brown <jim@audiosystemsgroup.com>
> To: rfi@contesting.com
> Subject: Re: [RFI] Question about common mode noise
> Message-ID:
> <91e3ff79-0e07-449d-8ea7-ca9f1056bec9@audiosystemsgroup.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> On 1/20/2025 7:09 PM, Bob WA2SQQ wrote:
> > He swears that if the noise increases when the shield is connected,
> that?s
> > a positive indication you have an abundance of common mode noise.
> >
> > I?m not so sure this is a valid test. Comments?
>
> It's certainly an indication of failure to do proper grounding and
> bonding. Coax shields should go to a lightning arrestor where they enter
> the building, ideally on the exterior wall of the shack. The arrestor
> MUST be bonded to grounding for the building, which, BY LAW, must be
> bonded to all other grounds in the building, including entry for power,
> telephone, CATV, satellite dish, and any other antennas.
>
> On the operating desk, all parts of the station must have their chassis
> bonded together by short, fat copper, and that must be bonded to the
> grounding for the building at the closest point. And all cable shields
> should be bonded to the chassis AT THE POINT where they enter equipment.
>
> If you've done all this, any common mode current on the shield is going
> to go into that ground bus to all of the driven rods, not into your
> radio or other equipment in your shack.
>
> Study N0AX's excellent ARRL book on the topic, to which I contributed
> extensively, and/or the pdf of slides for talks I've given at Pacifcon,
> Visalia, and to several ham clubs.
>
> 73, Jim K9YC
>
>
>
>
>
>
>
> ------------------------------
>
> Subject: Digest Footer
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> ------------------------------
>
> End of RFI Digest, Vol 264, Issue 12
> ************************************
>
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