"Unclaimed Mysteries" <theletter_k_andthenumeral_4_doh@unclaimedmysteries.net> wrote in message news:13f3v3cdjqesj66@corp.supernews.com> Richard Crowley wrote: >> "Charles" wrote ... >> >>>> Why is video inverted for transmission? >>> Noise in the black portion shows up more than in the >>> white. Black is transmitted at higher power, more >>> received signal. less noise. >> >> Yes, that is my recollection of the original explanation >> by the engineers & scientists who devised the system. >> >> We tend to forget how primitive things were back then >> (>50 years ago) by modern standards. I can't believe >> what they did with vacuum tubes ("valves") in those days.Especially if your name was Muntz. ;-)> A LOT of maintenance.Agreed. I once maintained equipment with about 400 "high reliability" tubes in it. MTBF: less than a day.
Why is video inverted for transmission?
Started by ●September 19, 2007
Reply by ●September 20, 20072007-09-20
Reply by ●September 20, 20072007-09-20
> Other than brief portions of the evening news the question arises: > What's the whole point in restoration these days? If OTA-TV really goes > digital some distant day we might not even bother buying a new set._________ Accurate colour reproduction requires accurate transmission of the luminance (brightness) value of each colour, which is set by a specific, DC-coupled voltage. If the video signal was transmitted using AC coupling, then luminance values would be a function of the average voltage of the video waveform. For that matter accurate monochome reproduction also requires DC coupling, but it is not as objectionable if not used (cheap TV set, etc). Also - the purpose of inverting video for transmission is to transmit the peaks of sync pulses at +100% modulation, which allows TV receivers to show the most stable picture in the presence of noise (eg, fringes of the coverage area of the TV station). RF RCA Broadcast Field Engineer, retired
Reply by ●September 20, 20072007-09-20
> Other than brief portions of the evening news the question arises: > What's the whole point in restoration these days? If OTA-TV really goes > digital some distant day we might not even bother buying a new set._________ Accurate colour reproduction requires accurate transmission of the luminance (brightness) value of each colour, which is set by a specific, DC-coupled voltage. If the video signal was transmitted using AC coupling, then luminance values would be a function of the average voltage of the video waveform. For that matter accurate monochome reproduction also requires DC coupling, but it is not as objectionable if not used (cheap TV set, etc). Also - the purpose of inverting video for transmission is to transmit the peaks of sync pulses at +100% modulation, which allows TV receivers to show the most stable picture in the presence of noise (eg, fringes of the coverage area of the TV station). RF RCA Broadcast Field Engineer, retired
Reply by ●September 20, 20072007-09-20
> Other than brief portions of the evening news the question arises: > What's the whole point in restoration these days? If OTA-TV really goes > digital some distant day we might not even bother buying a new set._________ Accurate colour reproduction requires accurate transmission of the luminance (brightness) value of each colour, which is set by a specific, DC-coupled voltage. If the video signal was transmitted using AC coupling, then luminance values would be a function of the average voltage of the video waveform. For that matter accurate monochome reproduction also requires DC coupling, but it is not as objectionable if not used (cheap TV set, etc). Also - the purpose of inverting video for transmission is to transmit the peaks of sync pulses at +100% modulation, which allows TV receivers to show the most stable picture in the presence of noise (eg, fringes of the coverage area of the TV station). RF RCA Broadcast Field Engineer, retired
Reply by ●September 20, 20072007-09-20
> Other than brief portions of the evening news the question arises: > What's the whole point in restoration these days? If OTA-TV really goes > digital some distant day we might not even bother buying a new set._________ Accurate colour reproduction requires accurate transmission of the luminance (brightness) value of each colour, which is set by a specific, DC-coupled voltage. If the video signal was transmitted using AC coupling, then luminance values would be a function of the average voltage of the video waveform. For that matter accurate monochome reproduction also requires DC coupling, but it is not as objectionable if not used (cheap TV set, etc). Also - the purpose of inverting video for transmission is to transmit the peaks of sync pulses at +100% modulation, which allows TV receivers to show the most stable picture in the presence of noise (eg, fringes of the coverage area of the TV station). RF RCA Broadcast Field Engineer, retired
Reply by ●September 20, 20072007-09-20
> Other than brief portions of the evening news the question arises: > What's the whole point in restoration these days? If OTA-TV really goes > digital some distant day we might not even bother buying a new set._________ Accurate colour reproduction requires accurate transmission of the luminance (brightness) value of each colour, which is set by a specific, DC-coupled voltage. If the video signal was transmitted using AC coupling, then luminance values would be a function of the average voltage of the video waveform. For that matter accurate monochome reproduction also requires DC coupling, but it is not as objectionable if not used (cheap TV set, etc). Also - the purpose of inverting video for transmission is to transmit the peaks of sync pulses at +100% modulation, which allows TV receivers to show the most stable picture in the presence of noise (eg, fringes of the coverage area of the TV station). RF RCA Broadcast Field Engineer, retired
Reply by ●September 20, 20072007-09-20
On Wed, 19 Sep 2007 21:08:28 -0800, glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:>John Larkin wrote: > >(someone wrote) >>>Why is video inverted for transmission? > >> So black, which is the sync pulse, which is the retrace blanking, gets >> lots of transmit power, so things tend to stay in sync. > >That is the reason I always heard. > >In addition, sync pulses are blacker than black to make sure that >they are not visible on retrace. > > > Max-black also make dc restoration work nicely. > >Why does it make it easier? > >-- glenThe thing you clamp to is not in the noise floor. John
Reply by ●September 20, 20072007-09-20
On Wed, 19 Sep 2007 19:04:31 -0700, "Richard Crowley" <rcrowley@xp7rt.net> wrote:>"Charles" wrote ... > >>>Why is video inverted for transmission? >> >> Noise in the black portion shows up more than in the white. Black is >> transmitted at higher power, more received signal. less noise. > >Yes, that is my recollection of the original explanation by the >engineers & scientists who devised the system. > >We tend to forget how primitive things were back then (>50 >years ago) by modern standards. I can't believe what they >did with vacuum tubes ("valves") in those days. >Yup. Gain was expensive (now it's essentially free) and DC coupling was difficult. And RF noise figures were ghastly, especially at UHF. John
Reply by ●September 20, 20072007-09-20
Arny Krueger wrote:> "Unclaimed Mysteries" > <theletter_k_andthenumeral_4_doh@unclaimedmysteries.net> > wrote in message news:13f3v3cdjqesj66@corp.supernews.com >> Richard Crowley wrote: >>> "Charles" wrote ... >>> >>>>> Why is video inverted for transmission? >>>> Noise in the black portion shows up more than in the >>>> white. Black is transmitted at higher power, more >>>> received signal. less noise. >>> Yes, that is my recollection of the original explanation >>> by the engineers & scientists who devised the system. >>> >>> We tend to forget how primitive things were back then >>> (>50 years ago) by modern standards. I can't believe >>> what they did with vacuum tubes ("valves") in those days. > > Especially if your name was Muntz. ;-) > >> A LOT of maintenance. > > Agreed. I once maintained equipment with about 400 "high reliability" tubes > in it. MTBF: less than a day. > >I can top that. I helped to maintain a 1500-tube (all but three of which were dual or triple purpose) analog computer back a little over 50 years ago. It was part of a Nike Surface-to-air missile system. The standard first try repair was to kick it in the area where we suspected the problem lay, which was effective more often than not. One day, though, a general was making an announced inspection tour; on that morning, of course, the computer failed. We applied the standard fix, but this time the fixer kicked too hard and caved in one of the doors. The general came in, looked around and asked "Did that fix it?" We told that it had, and he said "good!" and walked out. We hadn't even told him what had happened. And, incidentally, we called the van it was in the "pizza oven". You can't believe how much heat 1500 tubes put out unless you've been there. Viva la Solid State. Allen
Reply by ●September 20, 20072007-09-20
"Allen" <allen@nothere.net> wrote in message news:46f283e5$0$17145$4c368faf@roadrunner.com> Arny Krueger wrote: >> "Unclaimed Mysteries" >> <theletter_k_andthenumeral_4_doh@unclaimedmysteries.net> >> wrote in message news:13f3v3cdjqesj66@corp.supernews.com >>> Richard Crowley wrote: >>>> "Charles" wrote ... >>>> >>>>>> Why is video inverted for transmission? >>>>> Noise in the black portion shows up more than in the >>>>> white. Black is transmitted at higher power, more >>>>> received signal. less noise. >>>> Yes, that is my recollection of the original >>>> explanation by the engineers & scientists who devised >>>> the system. We tend to forget how primitive things were back then >>>> (>50 years ago) by modern standards. I can't believe >>>> what they did with vacuum tubes ("valves") in those >>>> days. >> >> Especially if your name was Muntz. ;-) >> >>> A LOT of maintenance. >> >> Agreed. I once maintained equipment with about 400 "high >> reliability" tubes in it. MTBF: less than a day.> I can top that. I helped to maintain a 1500-tube (all but > three of which were dual or triple purpose) analog > computer back a little over 50 years ago. It was part of > a Nike Surface-to-air missile system. The standard first > try repair was to kick it in the area where we suspected > the problem lay, which was effective more often than not. > One day, though, a general was making an announced > inspection tour; on that morning, of course, the computer > failed. We applied the standard fix, but this time the > fixer kicked too hard and caved in one of the doors. The > general came in, looked around and asked "Did that fix > it?" We told that it had, and he said "good!" and walked > out. We hadn't even told him what had happened. And, > incidentally, we called the van it was in the "pizza > oven". You can't believe how much heat 1500 tubes put out > unless you've been there. Viva la Solid State. ]My only comeback is that I had two of these 400 tube monsters and another smaller one with only about 200 tubes. Even so my total of 1,000 tubes falls short of 1,500. BTW, this was the Hawk system. Do I get bonus points if my monsters were in the open air (sun, rain and hurricane-force winds), on the top of 60-80 foot towers in the Everglades, complete with alligator-infested scenery that was mostly under water? Once I got *tired* of that, they moved me to Germany, where the radars were still in the open air (sun, sleet, rain, waist-deep snow and subzero temps), on individualized hilltops. The scenery in Germany included a 270 degree vista of a large valley, complete with farms, little towns, and a castle or two.
