pete@valid.UUCP (Pete Zakel) (01/10/86)
According to everything I have read, cable does not have the bandwidth for
carrying MTS signals. However, when I tune in to channels 4 and 20 (which
both broadcast in stereo, 4 is network, 20 is independent) the "stereo"
light on my Sony SL-HF400 VCR comes on, the LEDs show a difference between
the left and right channel, and I can hear the stereo effect. Channel
20, which is broadcast on cable on one of the cable channels, is quite
pleasant and noise free, whereas channel 4, which is broadcast on channel
4 on the cable, is quite noisy and irritating and I usually switch out the
MTS decoder. I haven't yet talked to channel 4's technical people to find
out what gives, but the cable company person was quite surprised to find
that I received stereo at all. She also said that they do not alter the
signal in any way, they just pass it along.
So what gives? Is my cable company unique? Or am I only getting part of
the stereo information sent out by the television station? And is there
any difference in bandwidth on the cable channels versus the normal channels --
as broadcast on the cable -- that would explain the differences between the
two tations' stereo quality?
-Pete Zakel (..!{hplabs,amd}!pesnta!valid!pete)rob@panda.UUCP (Robert S. Wood) (01/11/86)
I had the same experience. I called my cable company and asked them if I bought a stereo TV, would I get the local channels in stereo. They said no. They were wrong, I do get them. I fact, their MTV, simulcast on an FM frequency has been out of service for 2 weeks, and the local UHF music video station is being received in stereo from the cable.
dsi@unccvax.UUCP (01/11/86)
> According to everything I have read, cable does not have the bandwidth for > carrying MTS signals. However, when I tune in to channels 4 and 20 (which > both broadcast in stereo, 4 is network, 20 is independent) the "stereo" > light on my Sony SL-HF400 VCR comes on, the LEDs show a difference between > the left and right channel, and I can hear the stereo effect. Channel > 20, which is broadcast on cable on one of the cable channels, is quite > pleasant and noise free, whereas channel 4, which is broadcast on channel > 4 on the cable, is quite noisy and irritating and I usually switch out the > MTS decoder. I haven't yet talked to channel 4's technical people to find > out what gives, but the cable company person was quite surprised to find > that I received stereo at all. She also said that they do not alter the > signal in any way, they just pass it along. I am suprised that you have a problem with channel 4 - if your cable system is "normal" (i.e. channel 5 starting at 76 mc) then channel 4 should be one of the cleanest channels around. Some cable systems, in order to reduce cochannel disturbances and to maintain precise separation between channels, lock the low band channels to a multiple of 6.0 mHz, in which case there might be an "adjacent" channel to 4, a channel 5 which would be shifted 4 mHz negative. More likely, though, is that the BTSC signal is getting munged from two causes: 1) Multipath distortion. Cable TV systems do receive finite amounts of signal out of the air through the plant facilities (interconnecting wiring, taps, and so on) which are amplified by the line amplifiers and delivered to your home. This can be especially troublesome at low channel frequencies. If you are located in the "grade A" contour of the channel 4 signal, the chances for multipath distortion are very high. 2) Incorrect bandwidth inside the headend processing equipment. I doubt seriously that modern cable plants "pass the signal unattenuated." The Scientific-Atlanta series of channel processing amplifiers perform a complete downconversion to the TV I.F., do the processing at the IF, and then upconvert back to the desired channel. This is even true when the same channel is to be passed. The advantage of this is that "offsets" can be applied to the cable signal to reduce cochannel intermodulation effects. (Offsets are + 10 kc, - 10 kc, and 0 kc of the nominal pix carrier frequency). The filters inside these channel processors are very sharp and are implemented in SAW technology; some SAW filters do not have the proper slope characteristics for BTSC. If your cable company was stupid enough to use Catel or B-T channel processors in the headend, there is no telling what is happening to channel 4. Often times, when there is no upper adjacent channel on the basic-12, the cheapskate headend will install cheaper channel processors because the spillage doesn't affect anyone. 3) (Just thought of a third one) Modification of a television transmitter for BTSC is a * NONTRIVIAL TASK *. You just don't go out and get a BTSC exciter and plug it into the aural transmitter. Very extensive mods have to be made to the diplexer, output traps, and interstage coupling inside the aural transmitter, particularly if it was designed in the old days. IF diplexed transmitters don't have as many problems (check with your TV station on this....but most stereo generator people won't let you get away with just purchasing and installing it...) A marginal BTSC installation will "false" and so on in fringe conditions. 4) (A fourth cause) Heavy intermodulation distortion - where the line amplifier is no longer operating in the linear region - will destroy BTSC. OK, analog engineers, you wanna make some money? Design some channel processors and other goodies, as well as test equipment, so that the cable system will pass BTSC unmunged. (Note that if you have Zenith ZTAC boxes, you won't get BTSC at all...the signal is downconverted to baseband and remodulated.) I've solved this by erecting a - gasp - antenna! David Anthony DataSpan, Inc
spencer@oberon.UUCP (Randy Spencer) (01/12/86)
> According to everything I have read, cable does not have the bandwidth for > carrying MTS signals. However, when I tune in to channels 4 and 20 (which > both broadcast in stereo, 4 is network, 20 is independent) the "stereo" > light on my Sony SL-HF400 VCR comes on, the LEDs show a difference between > the left and right channel, and I can hear the stereo effect. Channel > -Pete Zakel (..!{hplabs,amd}!pesnta!valid!pete) The reason that it is said that there is no bandwidth in cable to broadcast stereo is because of the way the channels have been set up. When channels 2-13 and 14-83 were originally assigned frequencies they were given, by todays standards pleanty of guardband. When television started out the equipment was just not a precise as we make it today. As time went on however we ended up with television equipment able to do the job much better and with much less guard between different stations. Then came cable television. They were looking to put even more channels out there than there already were so that there would be no conflict with exhisting ones. The went up the frequency scale but after a while you are not talking electro magnetic any more, eventually you get into micro waves and the Light! They went to pack the new channels together (those above 83). When they were done they had a new standard that television makers could create tuners for. Well, along comes stereo AM and the next step is TV in stereo, heck, we don't need all that bandwidth, we will devote all that we can to getting the sound across. Great plan.. only for as long as cable keeps the channels the way that they are they will never be sending MTV out to our MTS tuners. However this does not limit the way that you receive broadcast channels, they are just passed on to you in the original form (easily discovered by connecting the TV w/o the cable box). Thus any channels 2-83 that broadcast in stereo in your area *will* make it to your house that way. ============================================================================== Randal Spencer Student DEC Consulting - University of Southern California Home: 937 N. Beverly Glen Bl. Bel Air California 90077 (213) 470-0428 Arpa: Spencer@USC-ECL or Spencer@USC-Oberon Bitnet: Spencer@USCVAXQ ------------------------------------------------------------------------------
brown@nicmad.UUCP (01/12/86)
In article <19@valid.UUCP> pete@valid.UUCP (Pete Zakel) writes: >According to everything I have read, cable does not have the bandwidth for >carrying MTS signals. However, when I tune in to channels 4 and 20 (which >both broadcast in stereo, 4 is network, 20 is independent) the "stereo" >light on my Sony SL-HF400 VCR comes on, the LEDs show a difference between >the left and right channel, and I can hear the stereo effect. Channel >20, which is broadcast on cable on one of the cable channels, is quite >pleasant and noise free, whereas channel 4, which is broadcast on channel >4 on the cable, is quite noisy and irritating and I usually switch out the >MTS decoder. Fortunately, the information about cable not being able to carry MTS TV stations has been a myth. But, there are conditions. 1) The cable company must use IF type receivers and not baseband receivers, at the head end. 2) Any cable converter used (if any) must also be of the IF type, not baseband type. The headend IF receiver is the receiver that is used to pick up the TV signal off the air and convert it to the cable channel needed. If the cable company gets the video/audio directly from the tv station, you will not get stereo, until a unit is put into place to get the stereo to the cable company and the cable company spends the money to put in the extra equipment required to put MTS on the channel. Our cable company is just like that. We get direct feeds from the stations involved (2 of them). One we get off the air, for now. The other, because the headend is so close to the station, makes antenna pick-up a little rough. But, both tv stations have plans to work with the cable company and help pick up the expense of getting the required equipment to get MTS on the cable channel, using direct feed. Now, in your case, I think that channel 4 is giving you trouble because you are receiving tv channel 4 on cable channel 4. Not good. What you will get is cable channel 4 and some of the off the air channel 4. MTS is very picky about its signal. Mixing two of them out of phase will cause problems. You will have to bitch at the cable company to move the channel around, ie, put cable channel 4 somewhere else. Hope this helps a little bit. -- ihnp4------\ harvard-\ \ Mr. Video seismo!uwvax!nicmad!brown topaz-/ / decvax------/
msc@saber.UUCP (Mark Callow) (01/22/86)
> When channels 2-13 and 14-83 were originally assigned frequencies they were > given, by todays standards pleanty of guardband. When television started .. > came cable television. They were looking to put even more channels out there > than there already were so that there would be no conflict with exhisting > ones. The went up the frequency scale but after a while you are not > talking electro magnetic any more, eventually you get into micro waves and > the Light! They went to pack the new channels together (those above 83). This is incorrect. Channels 14-83 are UHF broadcast channels. No cable system that I have seen can deal with UHF signals. They all deal with VHF. The extra channels are not obtained by squeezing the existing channels. They are obtained by using frequencies that in broadcast use are assigned for uses other than TV. For instance the so-called "mid-band" cable channels occupy space between TV channels 6 and 7. In broadcast use you will find several FM stations in that frequency band. > > However this does not limit the way that you receive broadcast channels, > they are just passed on to you in the original form (easily discovered > by connecting the TV w/o the cable box). Thus any channels 2-83 that Only channels 2-13 can be passed through "directly". And as someone else pointed out some cable systems' head ends demodulate even those to IF and remodulate. On our cable system the head-end equipment passes the MTS signal so broadcast channels 4 and 20 (4A and 3B on the dual cable system) MTS signals come through just fine (if you hook the cable directly to the TV) The problem is with the Zenith ZTAC descrambler/converter. It loses the MTS signal. -- From the TARDIS of Mark Callow msc@saber.uucp, sun!saber!msc@decwrl.dec.com ...{ihnp4,sun}!saber!msc "Boards are long and hard and made of wood"
msc@saber.UUCP (Mark Callow) (01/22/86)
> More likely, though, is that the BTSC signal is getting munged from
It is clear from the context in the referenced article that BTSC == MTS,
but what exactly does this latest piece of alphabet soup actually
stand for and what is wrong with using MTS like everyone else?
--
From the TARDIS of Mark Callow
msc@saber.uucp, sun!saber!msc@decwrl.dec.com ...{ihnp4,sun}!saber!msc
"Boards are long and hard and made of wood"brown@nicmad.UUCP (01/23/86)
In article <1914@saber.UUCP> msc@saber.UUCP (Mark Callow) writes: >It is clear from the context in the referenced article that BTSC == MTS, >but what exactly does this latest piece of alphabet soup actually >stand for and what is wrong with using MTS like everyone else? BTSC = Broadcast Television Systems Committee They are the people who decided upon the standard that would be used by all TV broadcast stations, for stereo. -- ihnp4------\ harvard-\ \ Mr. Video seismo!uwvax!nicmad!brown topaz-/ / decvax------/