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[TowerTalk] Re: [RFI] RFI/TVI, max. permissible electrical field

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Subject: [TowerTalk] Re: [RFI] RFI/TVI, max. permissible electrical field
From: n7ml@imt.net (Mike Lamb)
Date: Mon, 11 Jan 1999 19:25:13 +0000


Mike Lamb wrote:

> Eddie,
>
> I wish that what you said is true, but the FCC DOES require that we keep a
> record on file as to what the maximum emission levels are for our station on
> each and every antenna and frequency band!!!  I think it is a farce, but I 
> have
> complied anyway.
>
> 73/Mike, N7ML
>
> EDWARDS, EDDIE J wrote:
>
> > > Recently I learned from the neighboor that I was doing TVI/RFI on some of
> > > his electrical devices. He then called the OFCOM (like FCC in USA) that
> > > made electrical fields measures and found values up to 12 V/m.
> > >
> > > What is the maximal electrical field in [V/m] I am allowed to produce with
> > > my transceiver. In HB9 I was chocked to learn that it's only 1 V/m when I
> > > interfere with other electrical devices!
> >         [KØiL]  Hi Cedric,
> >         Sorry to hear abt ur problem.  A quick review of USA's FCC
> > regulations (97.307 & 97.313) shows a limitation only on spurious
> > (non-fundamental) signals.  There is of course a power limitation of 1.5KW
> > on the main (fundamental) signal within the ham bands as well.  But no
> > limitation at all that I can determine on Field Strength.
> >
> >         So you could theoretically, here in the USA, run 1.5KW into a
> > 20-25dbd gain antenna (no matter what the field strength is) as long as the
> > spurious signals coming out of the rig/amplifier are below 50mW and at least
> > 40dB below the mean power of the fundamental signal.
> >
> >         After years of dealing with consumer electronics RFI reports, the
> > FCC has placed the burden on the owner of the "RFI susceptible" electronics
> > if the ham station is within the Part 97 limits.  They no longer take any
> > RFI complaints since 99.9% were found to be susceptible equipment reacting
> > to legal and clean RF transmissions.
> >
> >         If your neighbor & you are still on good terms, I suggest you help
> > him eliminate the interference by adding filters to his equipment.  Most of
> > the time the RFI is from audio rectification in audio amplifiers and can be
> > "reduce" to an acceptable level using ferrite cores/beads to attenuate the
> > RF on wires going to/from loud-speakers.  I had to take my TV apart to
> > install these on the internal speaker wires, but there's no more TVI now!
> > (Happiness returned to KØiL's home)
> >
> >         Don't know if you have any Radio Shack stores (or equiv.), but you
> > can purchase ferrites there or from several sources in QST or CQ mags.  It
> > might be a good idea to purchase the ARRL's RFI Handbook to help determine
> > the RFI path into the "susceptible" equipment and how to properly install
> > these ferrites.
> >
> >         Keep this in mind at all times: Consumer electronics has practically
> > no RFI/EMI filtering and is NOT designed to operate near RF transmitters
> > since 99% of the time it does not have to.  It is necessary to add this
> > filtering in order for the device to operate properly near any RF
> > transmissions.
> >
> >         Now try to convince your neighbor of this FACT. ;^)  Good luck &
> > good DX!
> >
> >         73,
> >         de ed -KØiL
> >         k0il@qsl.net
> >
> > --
> > 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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