This is a relatively easy one. Television sets are intended to be receivers, they're just not particularly selective ones, if you and your neighbors arc on "cable/' and you're having TVI problems in your own home or those of your neighbors, the first order of business is to reduce the number of peripheral w ires connected in the cable signal line. If you (or your neigh bars) have appliances other than an approved cable TV converter box or a TV set connected, disconnect everything else (VCRs, preanips, switches, etc.) and see if the TVI persists.

The coaxial line from the cable service to the television set should be as direct as possible. Don't connect VCRs in this patht [f you need to use a VCR, as most of us do. connect its input/output pons using audio cables to the television's audio input/ video input and audio output/video output jacks. All Uie modem sets have such provisions. I see many licensed hams who have VCRs iind other accessories connected to their cable lines, when it incompletely unnecessary. Wh\ convert audio and \ ideo signals to Channel 3 and feed them into the TV's tuner when you 11 get far better results just plugging them directly into the audio and video amplifiers in the set, without using any RF? It doesn't make

If you're on cable, do not use a preamp. They're a total waste of time for cable television services. The sianal level from the cable should be sufficient to provide a gotxL strong signal to four, five, or six televisions without the need for iiny kind of preamplifixation. If you think you get "better reception" with a preamp in your cable line, either you're kidding yourself, or there's something seriously wrong with the signal level pro\ided by yotii cable company. Ask them to come out and perform a measurement on >our cable signal levei.

Thev all have small, hand-held devices which let them know1 immediately if your signal level is sufficient If it isn't, then it is their responsibility to tlx the problem, not yours.

Another warning if you're on cable: If your cable was installed more than a few years ago. it is \ery likely the service has deteriorated due to lack ol adequate maintenance. The coaxial cables used need to be replaced everj feu years. I hcy don't last forever. The connectors are not waterproof, and often fill up with water creating a reduction in signal strength and the possibility of mixing signals with your transmitter, which in turn creates interference. Connectors should be clean and dry. You can check them yourself, if you can reach them, if you disconnect the cable from the "feed*1 i either above or underground), and water drips from the connector, this is a real problem that needs to be addressed. Water in an RF connector almost always indicates that water wilt also be present in the coaxial cable attached to it. This, too, adds attenuation and reduces signal levels. Normally, maintenance of the cable right up to the entry point of >our home is your cable company's ;esponsibility. The cabie inside your home is normally your responsibility.

If you or your neighbors are not on cable, you may not have sufficient signal levels to override interference. Unless you can literally see the television transmitter's antenna from your TV antenna site, the signal will not be all that strong. Replace old, oxidized antennas vuth new ones, and make sure the> are properly aimed. Avoid using 300-ohm 'twin lead" for TV antennas! Use a 300-ohm-to-75-ohm balun instead, installed directly across the antenna terminals, and feed the antenna w ith high-quality, double-shielded RG59- or RG6-type

CATV coaxial cable, (RG6 "quad/" which has four shields and Is *M00r; shielded is an excellent choice, it's what the cable TV companies use. and it's not expensive,) If you don't have the proper crimping tool for type "F* TV connector installation, borrow or buy one. The best ones are not expensive, and are a good investment, since it seems these connectors are here to stay. If your TVI problems are from HF

(1.8-30 MHz) transmissions* try using a high-pass filter in the coaxial tine to your television set. with the filter installed right at the rear pane! connector or the TV. or bener still, inside the TV between the rear panel and Ihe tuner. Try grounding the case of ihis filter If that doesn't help or makes the interference worse, remove the ground.

A word about high-pass TV1 filters: These come in several "flavors," and performance is unrelated to cost in my experience. The most effective ones are really the 300-ohm "twin lead" filters, uhere each side of (he balanced line is filtered. Unfortunately, ihe most effective TV transmission line is coaxial cable, not twin lead. Herein lies a dilemma. but it's an easily solved one. For stubborn cases of TVl, Tve often found that using a coaxial feed line to the back of ihe set, followed by a 75-ohm (coax)-to-300-ohm (twin lead) balun, followed by a 300-ohm high-pass filter, followed by another 300-ohm (iwin leadi-to-75-ohm (coax) balun. into ihe ! V sets tuner is what works besL Sure, it seems crazy to transform from coa\ to t\\ in lead and then from twin lead back to coax again just to install a 300-ohm filter, but there is a method to this madness.

The problem with most 75-ohm coaxial cable high-pass filters is that while they do a splendid job rejecting interference conducted within ihe cable, they do absolutely zero for "common-mode" interference, which is carried on ihe outer conductor of ihe coaxial cable. Such interference conducts right past a 75-ohm coaxial filter and enters the television set on the outer conductor (shield) of the cable alone, and can create nightmarish problems. By breaking up the cable's shield using isolation transformers and a balanced filter, such common-mode interference is thwarted by the "broken circuit" created. (PS.—Good 75-ohm-to-300-ohm baluns, and 300-ohm highpass filters, have almost no insertion loss, so don't worry about losing a lot of signal strength with this system. If you use good coaxial cable and a good 300-ohm filter, it won t happen.)

[f ihe interference problems are from VHF-UHF transmissions, the best highpass filter in the world won't help. You'll need to use a "stub." which is tuned to reject the specific frequency of the interfering signal. Such a "stub" will need to be one quarter-wave length long,

measured in coax; at the interfering frequency, and connected in parallel with the coaxial feedline to your TV set's tuner, as close to the tuner as possible. One quarter-wavelength in coax will be shorter than a real quarter-wavelength because the length needs to be corrected by the velocity factor of the coax used, For solid-polyethylene coaxial cable types, the velocity factor is usually 0.66; for "foam" dielectric coaxial cable types, the velocity factor is higher typically 0.78 lo 0.80 or so. Such a "stub** is easily connected to the backside of a television receiver using a "T1 (or "tee") adapter having a single type F male fitling and two type F female receptacles. Such items can be picked up for a couple of dollars at Radio Shack or similar retail stores. By the way, in you didn't know, a quarter-wave "stub" rejection filter has no connection to the "open end" oT the coax. Don't short-circuit ihe open end, and don't terminate ii with anything, or it will be completely ineffective, The quarter-wave "stub" works on the principle that the impedance of a transmission line is inversely proportion al to its termination impedance every quarter-wave. If you leave a quarter-wave stub open-circuited at one end. the reflected impedance will he a short circuit at the opposite end, on the frequency where the stub represents a quarter-wavelength in coaxial cable. Thus, a quarter-wave -topen-circuited" stub will look like a short circuit on its resonant frequency, and will shunt interference u> ground. It works.

If you try hard enough. TV! is possible to eliminate. I ve never seen a situation yet where I couldn't do it. It may take several hours, it may take a few dollars, but it can always be done.

Telephone Interference

This is a broad category that applies to all appliances connected to a telephone line: telephone instruments, computer modems, fax machines, etc.

Telephone interference is rare at VHF-UHF levels, bul can be very troublesome at HF. One reason is that VHF-UHF signals are quite well shunted to common by the capacitance of the lines and instrument ^ connected to them, but at HF this isn't the case. Another reason is that wavelengths are so much longer at HF that the near field interfering signals might be as far as a few hundred feet away on HK w hile the near field is very short on VHF-UHF, Radialed signals are reduced in intensity b\ an iiuerse square law based on the wavelength being used. White (00 feet is very "close" on 80 meters, ii is very "far away" on 2 meters.

Many telephone interference problems can be eliminated by terminating unused jacks. Since telephone lines are often "daisy-chained" (connected from jack to jack lo jack within the house), any unused jack wiring becomes an antenna w hich can be an efficient receptor of signals. If you have telephone jacks in your home (or a neighbor's home) which are unterminated ino telephone instrument connected), these can cause problems. The easiest solution is to terminate them, whether a telephone instrument is used there or not, with correct passive terminations. Such terminations provide a500-ohm terminating impcdance (not a resistance alone!) across ihe line, simulating a real telephone-type instrument, and they are available for a couple of dollars from your local phone company or at Radio Shack.

If you've tried this and still have interference problems, try another trick: Go to the point of entry of the telephone line to the house and find the connection box located there, This is often a four-terminal "block" with brass machine screws, flat washers and nuts, where the telephone line from the utility connects to the house telephone Wiring. Frequently, you will find unused wires just "floating" (not connected to anything) there. Any and all wires floating at this point (wires just tw isted together and not connected to anything) can be grounded, since they're noi being used, anyway. Strip the insulation off the unused w ires, twist the exposed copper conductors together, and tie them to the nearest ground post, which is likely to be close by, since the telephone utilities usually provide an earth ground inside of or nearby ihis junction box. By grounding unused conductors in telephone wiring, you can short out some RF current which might be causing interference directly to ground. Also, since telephone wiring is often twisted" along its route. grounding unused conductors tends to "'shield'1 the entire bundle of wires, which can also help reduce RF interference.

If you try both of the measures outlined above and still have interference problems, try using single-ins truraenL telephone filters. These are sold by many manufacturers as "aftermarket" fixes, and usually have modular telephone plugs and jacks included. Ii telephone filters are used, they often work best when installed right at the telephone instrument (or computer modem, or FAX modem. or whatever), as close as possible to the equipment. Don't bother installing a telephone filter at the wall receptacle when a cord will be used between the wall socket and the instrument. It will be much more effective when used right at the telephone (or whatever). Sometimes a filter might he neccssLiry in the handset cord as well. I've even seen situations where one filter did very little to reduce interference, but two or three filters in series at the same point worked perfectly. These filters usually retail for about $!0 each and, if the\ work, are well worth the investment,

If you tr\ all the tricks above and still havL' telephone interference, take a look at how your antenna transmission line is routed. Is it close to. or in parallel with, your (or your neighbor's) household telephone wiring? If so. move it! Is your HF antenna close to the telephone wiring from a street utility pole to your home? M'so, move ii! You are free to reroute telephone wiring as required to cure interference problems. You don'i need the telephone company's permission, Just be sure that if you do reroute telephone wiring outdoors, use the telephone company's original cable, which is designed to withstand the abuses of mechanical stress and weather. Inside your hume, these factors arc unimportant and you can prett\ much do whatever you want, since you own this wiring, anyway.

If in the process of investigating telephone interference you happen to find frayed. worn, or broken cables outdoors (between ihe telephone company's street wiring and your hornet call the phone company and ask them to replace it. lie-ware of telephone lines. As benign as they look, they do cany a "ring" voltage capable of inducing quite a shock, and I hey need to be wel! insulated. Don't handle exposed conductors with bare hands. (This hazard only exists during a "ring," but you never know when that might occur.)

You might also try different telephone instruments. The complicated ones with electronic memory for telephone number storage and redial are sometimes more prone to interference than the old-fashioned "no frills" phones, purely because they contain additional electronic circuitry The old Western Electric-built telephone instruments (remember the 1960s and 1970s?) which had a simple one-transistor tone oscillator, carbon microphone element and mechanical beli ringer were pretty "bulletproof' compared to most of the cheapie imports we use today. You can still find these simple but effective telephones, both new and used, If worse comes to worst and you can't fix a telephone interference problem, try calling the phone company. Although

"Grounding station equipment can also help prevent lightning damage in the event of a direct or secondary strike, but is by no means a 'fail-safe9* precaution.

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