owner-rfi@contesting.com wrote:
> >From k3lr Mon Mar 9 22:17:02 1998
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To: <rfi@contesting.com>
> Date: Mon, 09 Mar 1998 19:07:24 -0800
> From: Cortland Richmond <ka5s@saber.net>
> Reply-To: ka5s@saber.net
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> To: Kelly Boswell <kboswell@aetn.org>
> CC: rfi@contesting.com, cortland_richmond@optilink.dsccc.com
> Subject: Re: [RFI] RFI into a microphone
> References: <3980718046.71680249@aetn.org>
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>
> As it happens, I've dealt with this problem for telephone equipment
> and what worked for me may
> work for you. Wind a 2-conductor, common-mode choke of around 2 or 3
> milli-Henries. Not
> "micro-Henries." Be sure TWO conductors are wound on it. Connect
> mike hot to one, mike return
> to the other. Do not ground _either_ conductor until the line gets
> where it's going; the
> "ground" there is just as hot as anything else. But you know that
> already, don't you!
>
> We've used a toroid core about 1 cm across, mu about 5000. This is
> NOT a Radio Shack RFI core,
> but you may be able to salvage a core from their grab-bag. Look for
> something from a switching
> power supply. I forget how many turns we used, maybe 40? The choke
> may even be self-resonant
> near the frequency you wish to eliminate, which is all to the better.
> If you don't feel up to
> doing it yourself, there is an outfit that sells 2-wire common-mode
> filters (no ground needed!)
> and I'll look it up when I go to work in the morning.
>
> Cheers,
>
> Cortland, KA5S
>
> Kelly Boswell wrote:
>
> > Hi gang. My colleague at Idaho Public Television is asking for
> suggestions.
> > An AM station gets into his microphone lines. Reply to me, I'll
> forward.
> > TNX
> > Kelly Boswell, Arkansas Educational Television
> > KA5MGL
> > kboswell@aetn.org
> >
> --------------------------------------------------------------------------------------------
>
> >
> > Thought I would throw this one out to you all. We're in pledge
> right now( who
> > isn't?) And I have a terrible problem with the local (2 miles away)
> am radio
> > station getting into my mics. I have actually measured about 400
> millivolts
> > of rf coming off of our lighting grid !! Any ideas on how to get
> rid of this
> > problem? I have used bypass capacitors on the mic lines, tried
> extra
> > grounding, and tried no grounding, all to no avail. I'm stumped as
> to what to
> > do. It wouldn't be so bad if it was a nice station to listen to,
> but it plays
> > pretty old stuff!! (just kidding!)
> > Any ideas would really be appreciated..
> >
> > Rich Van Genderen, Idaho Public TV
> >
> > --
> > Submissions: rfi@contesting.com
> > Administrative requests: rfi-REQUEST@contesting.com
> > WWW: http://www.contesting.com/rfi-faq.html
> > Questions: owner-rfi@contesting.com
--
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