Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 exptools 1/6/84; site ihuxf.UUCP Path: utzoo!linus!decvax!harpo!ihnp4!ihuxf!parnass From: parnass@ihuxf.UUCP (Robert S. Parnass, AJ9S) Newsgroups: net.audio,net.tv Subject: curing interference to TV and stereo Message-ID: <1702@ihuxf.UUCP> Date: Thu, 12-Jan-84 12:05:14 EST Article-I.D.: ihuxf.1702 Posted: Thu Jan 12 12:05:14 1984 Date-Received: Fri, 13-Jan-84 06:53:55 EST Organization: AT&T Bell Labs, Naperville, IL Lines: 112 x 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. -- ============================================================================ Robert S. Parnass, AT&T Bell Laboratories, ihnp4!ihuxf!parnass (312)979-5760