| Home | Audio mag. | Stereo Review mag. | High Fidelity mag. | AE/AA mag.
Departments | Features | ADs | Equipment | Music/Recordings | History |
|
Further Notes on CATV Having worked for some time in community antenna (cable) TV, / was interested in your reply to Keith Webster's letter in April. Connecting additional sets to the cable without additional payment (and usually without the right equipment) would be frowned upon-at the very least. This is especially true if, as is often the case, such connection causes interference to non -subscribers in the area. In apartment complexes and crowded suburban areas, with some people on the cable and others using their own antennas, it's almost impossible to keep the CATV signals from causing interference to non subscribers. Everyone of the non -subscribers feels, justifiably, that he has a right to proper reception (from the "free" airwaves), whether or not some people who have CATV service want to cheat the CATV company by hooking up extra sets to their cable connection. This situation was 'typified by one customer we had in Poughkeepsie. This man had decided he was dissatisfied with having just one set hooked up to the cable tap we installed for him. He wanted an upstairs bedroom set connected also. He ran a long piece of regular 300-ohm twin lead (flat TV lead-in) from the downstairs set, over the house, to the upstairs bedroom on the other side. It worked fine for him-but it interfered with the reception on 50 to 100 non -subscribers' sets in the area-out to a couple of hundred feet from his house. The twin-lead, being unshielded (cable TV uses co -axial, hence self shielding leads) would radiate a signal which resulted in a vertical bar being displaced at varying distances across the picture (on nearby non -subscribers' sets tuned to the same channel). The bar was caused by the delay introduced by the CATV system, which might be more, or less, than (but never quite the same as) the delay in the regular, non-system reception. In some severe cases, the interference could even wipe out the color. On another occasion I had to disconnect a subscriber because his set was radiating its own i.f. signal like the devil's own interference. What had happened was that someone had "fixed" his tuner and, in replacing it in the set had left off its shielding. If anyone has trouble with this sort of interference or suspects that this is the cause, it can be tracked down as follows. Get a directional TV antenna and a portable TV set and stick them in a car (or pickup truck to make rotating the antenna easier). Or try a pair of "rabbit ears" for the antenna, spread straight out like a folded dipole. Tune to the station being distributed on the cable, and drive around. When you see the picture coming in bright and clear from one of the houses, drive around it. We used to check for unauthorized multiple taps that way, and we always found either an unauthorized 300 ohm twin-lead tap, or that the signal was coming from someone's improperly-operating TV receiver tuner. To multiply the sets operating off a cable the subscriber should do what the cable company does, use a 75 ohm to 300-ohm matching transformer at each end of a length of RG59U coaxial cable. -George W. Brooks; Poughkeepsie, N.Y. (Oct. 1975, JOSEPH GIOVANELLI) = = = = |
Prev. | Next |