parnass@ihuxf.UUCP (Robert S. Parnass, AJ9S) (01/12/84)
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In most cases of interference to television and high fidel-
ity equipment, the Federal Communications Commission (FCC)
has found that the fault lies with the receiving equipment,
rather than the transmitting equipment. Most consumer elec-
tronics equipment is built with inadequate shielding and
filtering.
Having experience in this area, I recommend the following
steps to deal with interference to high fidelity equipment:
1. Look for tarnished or loose ground (shield) connec-
tions on your interconnecting cables between the
tuner, tape deck, or turntable and amplifier. A poor
contact can act like a diode, detecting radio fre-
quency (RF) energy.
2. To prevent the speaker cables acting like antennas,
you can:
a. Bypass the RF signal to ground, by placing a
.01 microfarad disk capacitor across each pair
of speaker terminals on your amplifier.
b. Install a J. W. Miller filter in the speaker
leads, especially designed for this purpose.
I've found these filters in electronics stores
catering to TV repairmen.
3. Radio signals from nearby transmitters may be induced
into the AC line wiring. If this is the case, an AC
line filter may eliminate the problem. A Cornell-
Dubilier filter worked in my situation.
4. In severe cases, RF energy may enter stereo equipment
through the cabinet. Elimination may involve spraying
the interior of plastic cabinets with an RFI spray
(like aguadag), or better bonding in the case of metal
cabinets.
You may find that all or a combination of these steps must
be applied to alleviate your problem.
Those experiencing television interference should first
install a high pass filter between the TV tuner and the
antenna. Industry is resisting proposed FCC legislation
that would require decent filtering in home entertainment
equipment. Filtering is so poor that many manufacturers,
such as RCA, Zenith, and Quasar1, will provide one free if
furnished with the serial number and model number of the TV
or video cassette recorder (VCR). I've received free
filters from RCA2 and Zenith3 to use on TV's manufactured by
them. For a complete list of manufacturers providing assis-
tance, write the American Radio Relay League4 (ARRL).
If you are impatient, purchase a good high pass filter. A
decent, American made filter is sold by Radio Shack (#15-
580, $8.95). The cheaper Radio Shack filters perform
poorly.
Other suggestions include:
+o Those cheap switches that connect TV's to video games
and computers invite interference. Disconnect them
completely.
+o An AC line filter on the TV will help if radio signals
are induced into the AC wiring.
+o An outdoor TV antenna will help increase the strength
of the TV signals, which are in competition with the
those of the radio transmitter.
+o Use coaxial cable feedline to the antenna. Twin lead
provides effective shielding in theory5, seldom in
practice. It performs poorly if bent, or run near
metallic objects.
+o Rusty antenna hardware causes diode action, inviting
trouble. Weather seal all outdoor connections.
Curing interference to home entertainment devices is a mul-
tifaceted problem. With the increasing population density,
and the proliferation of unshielded, unfiltered TVs', VCR's,
stereos, and computers, electromagnetic compatibility prob-
lems are only going to get worse.
__________
1. Quasar Service Center, c/o Carl Rom, telephone
(312)451-1200, x3335.
2. RCA Consumer Products, Indianapolis, IN, c/o Justin J.
Sanchez, telephone (317)267-6445.
3. Zenith, Art Kaas, telephone (312)671-7550.
4. ARRL, 225 Main Street, Newington, CT 06111, telephone
(203)666-1541.
5. Twin lead is a balanced line in free space.
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Robert S. Parnass, AT&T Bell Laboratories, ihnp4!ihuxf!parnass (312)979-5760 burris@ihopa.UUCP (David Burris) (01/12/84)
I thought the law required the offending transmitter to correct the problem. To the best of my knowledge, it is illegal for ANY transmitter to interfere with commercial transmissions. Depending on how diplomatic you feel, you can require the person who owns the transmitter to pay for correcting the problem or contact the FCC. -- Dave Burris ..!ihnp4!ihopa!burris AT&T Bell Labs, Naperville, Il.
jj@rabbit.UUCP (01/12/84)
Sorry, Dave, for once I have to disagree with you. The transmitter must be within spec, and that's IT. (Otherwise, you would be holding the transmitting entity responsible for the failure of the interfered entity.) The FCC is quite emphatic on this. Despite this, a lot of ham radio operators, etc, will go to extreme ends in order to help out people who are having interference problems just as a matter of public relations. The law (and the FCC ) do require the transmitter to be "non-offending". They also, however, define the word "offending" to indicate a malfunction of the transmitting equipment. Poorly designed equipment that is being interfered with is specifically NOT the fault of the transmitter. -- TEDDY BEARS ARE PEOPLE, TOO! (allegra,harpo,ulysses)!rabbit!jj
parnass@ihuxf.UUCP (Robert S. Parnass, AJ9S) (01/12/84)
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Dave Burris asserts:
"I thought the law required the offending transmitter
to correct the problem. To the best of my knowledge, it
is illegal for ANY transmitter to interfere with com-
mercial transmissions. Depending on how diplomatic you
feel, you can require the person who owns the
transmitter to pay for correcting the problem or con-
tact the FCC."
This is not true!
My new neighbors contacted the FCC, complaining that my ama-
teur radio transmitter interfered with their TV. Their TV
did experience interference, along with their VCR, Western
Electric Trimline (R) telephone, and cassette deck.
The FCC requested that I demonstrate to the complainants
that my transmissions did not interfere with my own TV. I
complied and was absolved from any further responsibility.
Although I was advised by the FCC that I had no obligation
to repair the complainants' equipment, I voluntarily spent
many hours installing filters in their sets and putting up
an outside antenna for them. This was just to be a good
neighbor.
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Robert S. Parnass, AT&T Bell Laboratories, ihnp4!ihuxf!parnass (312)979-5760 caf@cdi.UUCP (caf) (01/14/84)
Unless the offending transmitter is radiating harmonics (rare except for CB's with illegal amplifiers), most Amateur etc. interference to TV/stereo is due to poor design in the consumer equipment. The consumer electronics industry has a long history of producing RFI-prone products while at the same claiming to the government that there is no serious problem. That charade shouldn't "fly" too much longer when the FCC mandates EMC standards for consumer equipment. Unfortunately, such standards will not be retroactive. -- Chuck Forsberg WA7KGX CDI Portland OR (503)-646-1599 cdi!caf