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[RFI] RFI/TVI, max. permissible electrical field

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Subject: [RFI] RFI/TVI, max. permissible electrical field
From: EDWARDS, EDDIE J" <eedwards@oppd.com (EDWARDS, EDDIE J)
Date: Mon, 11 Jan 1999 12:55:54 -0600
> 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

        Now try to convince your neighbor of this FACT. ;^)  Good luck &
good DX!

        de ed -KØiL

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