brian@sdcc3.UUCP (Brian Kantor) (12/29/84)
> In article <293@mhuxm.UUCP> abeles@mhuxm.UUCP (abeles) writes: > >But, WHAT DOES CABLE READY really mean? A quick explanation: In order to squeeze in those extra cable channels, the cable companies use frequencies on the cable that are not available for over the air broadcast use. A ``Cable Ready'' set can receive these without a converter box. Why would you want such a thing? Well, your remote control would then allow you to select the cable channels as well as the regular broadcast channels. Much nicer than having two separate remote controls - one for the TV and one for the cable box. You would still need a descrambler box if the cable channel you want to get is scrambled. How it works: Broadcast television is sent in three main frequency bands low-vhf channels 2-6 high-vhf channels 7-13 uhf channel 14 and up Between these bands there are other over-the-air transmissions; for example, between channel 6 and 7 is a large span of frequency space that contains FM broadcast, satellite telemetry, aircraft, public service [police, fire, etc], and military band allocations. But those people aren't on the cable. Because the cable keeps those signals out and its own signals in, it is possible to use these frequencies for additional television channels on the cable. The frequencies below channel 2 are sometimes used. Most popular for cable systems are the ``mid-band'' channels between 6 and 7, and on cable systems with lots of additional channels, the ``super-band'' channels above 13 are used. Most cable systems do not use the UHF channel space because the cable attenuates the signal too much for practical use. A cable-ready tuner is generally one that has additional channel slots, any of which can be tuned to either the standard broadcast channels or to the special cable channels. It is important when selecting a set to make sure that the cable ready tuner covers the bands used by your cable company. In particular, many early cable-ready sets did not tune the ``super-band'' channels because they were not much in use. I am not aware of any TV sets available with built-in descramblers, although such may exist. In my area there are a couple of scrambling systems in use, one of which depends on notch filters to attenuate the ``premium'' channels you aren't supposed to be getting, and the others which depend on munging or removing the synchronization signals from the transmitted signal. On those, a special box recovers the sync signals (either from another special non-tv channel or from the aural carrier or from some other magic source). You have to pay extra for the box to descramble the premium channels. A side note: one cable system here is using addressable boxes. The same box can be turned on or off remotely for each individual premium channel, so you can buy just the ones you want, and change your available selections with just a call to the cable company. Evidently there is a digital code sent out somewhere on the cable to do that selection and all the cable company has to do is tell their computer to change what your box is doing. Note to cable thieves: yes, it is possible to detect that you are watching channels that you aren't paying for. Your cable box (and a cable-ready tv) mix the incoming channel with another signal (called the local oscillator) in order to process it further and extract the picture and sound [the ``heterodyne'' principle]. This local oscillator is what is varied by the tuner when you select a channel on the TV or on the cable box. Trick is that a little of that signal leaks out of your house, and can be received by a detector truck. From its frequency, it is possible to calculate what channel you are watching. Thus, the cable TV company CAN tell what channels you watch without entering your home. Most don't, because its expensive in manpower and the equipment itself isn't cheap, but THEY CAN DO IT if they want to. The Post Office in Great Britain does something similar to look for unlicenced TV sets. Brian Kantor UC San Diego decvax\ brian@ucsd.arpa akgua >--- sdcsvax --- brian ucbvax/ Kantor@Nosc Ticking away the moments that make up a dull day Fritter and waste the hours in an offhand way...