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

[Blackburn]

Hi,

Just though I'd add a little more information.  K0IL is correct that the
U.S. does not regulate transmitted fields from amateur stations in terms of
generating susceptibility to consumer electronics, however, the U.S. DOES
regulate RF field levels, including those from amateur stations, for
purposes of personnel exposure to RF radiation.  U.S. amateurs are
currently required to perform an RF safety evaluation on their installation
and take appropriate measures to preclude personnel exposure in excess of
the levels defined in the FCC rules.

A good summary of the requirements can be found at
http://www.arrl.org/rfsafety/.  The actual regulations, FCC bulletin 65,
and an FCC prepared supplemental manual for amateur radio operators can be
downloaded from the FCC website 
(http://www.fcc.gov/oet/info/documents/bulletins/).

Unfortunately for people experiencing RFI, the levels permitted for
personnel exposure are significantly above the levels at which a lot of
consumer electronics will upset, particularly when one considers that
personnel exposure is based on field levels averaged over a period of time.
 A field level of 1 volt/meter in the HF region is probably below the
inherent susceptibility level of most consumer electronics, but as HB9HFN
has noted limiting emissions to this level at some reasonable distance
won't do much for your DXCC country total.   Note that members of the
European Union do impose RF immunity requirements on consumer electronics
currently marketed within these countries, but that doesn't help fix older
devices.

The ARRL web site also has a bunch of references on fixing RFI.  Be careful
what you do to someone else's consumer electronics, or you may find
yourself buying them a new unit.  Installing common mode chokes on power
cords and external wiring is a good place to start, since these can
generally be installed without voiding equipment warrantee or making mods
to the equipment itself.  Keep in mind that a single ferrite bead or core
(even a large one) will have almost no effect at HF.  Multiple turns (8 -10
maybe) through a split core such as those sold by Radio Shack or MFJ can
help.

Good luck.  Hope this helps.

Keith
KB6B

----------
> From: EDWARDS, EDDIE J <eedwards@oppd.com>
> To: 'Cedric Baechler HB9HFN' <cedric.baechler@com.mcnet.ch>;
rfi@contesting.com
> Subject: RE: [RFI] RFI/TVI, max. permissible electrical field
> Date: Monday, January 11, 1999 10:55 AM
> 
> 
> > 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
> 
> 
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