The television channel is 6 Mhz wide! Any signal transmitted in this 6 Mhz spectrum will cause noticeable interference to a television signal! Even a signal that is 40 dB weaker than the television signal will result in perceptible interference. There are a number of cable channels that we as amateurs can have problems with. These cable channels roughly, if not exactly, correspond with these Amateur Bands:

• Cable 2 [ 2] (55.55 Mhz) = 6 Meters
• Cable 17 [ D] (139.25 Mhz) = 2 Meters
• Cable 18 [ E] (145.25 Mhz) = 2 Meters
• Cable 23 [ J] (217.25 Mhz) = 1.25 Meters
• Cable 24 [ K] (223.25 Mhz) = 1.25 Meters
• Cable 64 [UU] (421.25 Mhz) = 70 Centimeters
• Cable 65 [VV] (427.25 Mhz) = 70 Centimeters
• Cable 66 [WW] (433.25 Mhz) = 70 Centimeters
• Cable 67 [XX] (439.25 Mhz) = 70 Centimeters
• Cable 68 [YY] (445.25 Mhz) = 70 Centimeters
• Cable 69 [ZZ] (451.25 Mhz) = 70 Centimeters
Be advised that there are no stipulated rules as to what channel number designator has to be on what frequency. (This is supposed to be a closed system!) These channels and frequencies may vary from one cable area to the next, although most cable systems use one of three "standard" systems. (The nice thing about standards is that there are so many to pick from!)

This interference can go both ways! In the majority of the cases reported, the interference was caused to the cable by the amateur. But there have been instances where there have been large enough leaks from the cable system to interfere with the amateur! From what I have seen, these instances have been created by either an improperly terminated cable ends (unconnected!), or by customer-installed "illegal" hookups. Rarely, the problem can be caused by a bad cable distribution amplifier or shield break somewhere on the pole cable.

As an example, I was receiving a S9 carrier on 145.250 on my packet radio. My radio was an Icom 28H and I had an 11 element vertical beam at 60 feet. I reported this to my cable company. A few days later they sent out their Engineer and DF Vehicle. I brought him up in my shack and showed him the interference. We used my beam antenna to determine that the interference was coming from a beam heading of 315 degrees (NW). We went to our vehicles and found on that heading, the offending equipment 500 yards away! It was an improperly terminated connector inside someone's house! An illegal hook up! So you can imagine what a bad distribution amplifier outside your window will do! Most of these leaks can be easily located with your HT or a hand held scanner. These are a few frequencies to listen for:

• Cable Channel 17 (D) --- Audio at 143.75 Mhz.
• Cable Channel 18 (E) --- Video at 145.25 Mhz.
• Cable Channel 18 (E) --- Audio at 149.75 Mhz.
• Cable Channel 23 (J) --- Audio at 221.75 Mhz.
• Cable Channel 23 (J) --- Video at 223.25 Mhz.
With an FM Handi-Talkie or scanner receiver the audio frequencies will seem to be distorted and over deviated , but obviously audio! On either the FM or AM the video carrier will sound just like an unmodulated carrier.

If leakage from the cable system caused harmful interference, it is the responsibility of the cable operator to eliminate the interference, regardless of the cause. If they determine that the leakage is coming from a subscriber's home, they must, if necessary, disconnect that home until the cause of the interference is found and corrected.

Part 76 of The Federal Communications Commission Rules and Regulations, which governs the Cable Industry, clearly states:

76.613 Interference from a cable television system. (a) Harmful interference is any emission, radiation or induction which endangers the functioning of a radionavigation service or of other safety services or seriously degrades,obstructs or repeatedly interrupts a radio communication service operating in accordance with this chapter. (b) The operator of a cable television system that causes harmful interference shall promptly take appropriate measures to eliminate the harmful interference.

There is much more to be read out of this part of the FCC Rules and Regulations and can be seen at yourlocal Field Operations Bureau if you are interested.

In these bulletins, I am going to focusmostly on the type of interference caused to the Cable Channel 18, 24, and 64-68. The reason for this is two-fold. One, is because these are the channels that most commonly experience fundamental overload interference from amateur stations, and, two, because any interference caused by amateur stations to these cable television channels is clearly not the legal responsibility of the amateur. Depending on the ultimate cause of the problem, it may be the responsibility of the cable operator, the TV manufacturer or the subscriber.

(Continued in Part 3)

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