Jerry Avins wrote: (snip)> Sure it works. That's what's behind heterodyning. The modulated signal > is, of course, narrow band at the original frequency. The intercarrier > TV sound carrier is at 4.5 MHz. I brought it out of one set into a > push-push diode frequency doubler (aka full-wave rectifier) and into the > retuned IF (10.7 MHz to 9) of a broadcast FM tuner. Listeners were > surprised to hear how good the actually broadcast sound was. In service > like that, the intermodulation products are easily removed by minimally > selective filters.As I understand it until about 1980, TV sound was sent through telephone lines while the video went through microwave links. Around then the technology changed such that the sound also went through microwave links. At about the same time the public was getting more interested in better quality TV and especially better sound. Pioneer produced a HiFi quality TV audio tuner, the standard for stereo and SAP for TV audio was developed, and other improvements in the audio section of available TV sets such as line level outputs were available. Thus more incentive for broadcasters to transmit high quality audio. -- glen
Frequency multipliers: A way around Nyquist limitations?
Started by ●July 12, 2005
Reply by ●July 15, 20052005-07-15
Reply by ●July 15, 20052005-07-15
glen herrmannsfeldt wrote:> Jerry Avins wrote: > (snip) > >> Sure it works. That's what's behind heterodyning. The modulated signal >> is, of course, narrow band at the original frequency. The intercarrier >> TV sound carrier is at 4.5 MHz. I brought it out of one set into a >> push-push diode frequency doubler (aka full-wave rectifier) and into >> the retuned IF (10.7 MHz to 9) of a broadcast FM tuner. Listeners were >> surprised to hear how good the actually broadcast sound was. In >> service like that, the intermodulation products are easily removed by >> minimally selective filters. > > > As I understand it until about 1980, TV sound was sent through telephone > lines while the video went through microwave links. Around then theThat surprises me. The sound subcarrier fits well within the 6 MHz allotted to a TV channel. and an ordinary phone channel doesn't have the bandwidth customary for broadcast. I wonder it that's just a myth.> At about the same time the public was getting more interested in > better quality TV and especially better sound. Pioneer produced > a HiFi quality TV audio tuner, the standard for stereo and SAP > for TV audio was developed, and other improvements in the audio > section of available TV sets such as line level outputs were > available. Thus more incentive for broadcasters to transmit > high quality audio.High-fidelity TV tuners imply high-fidelity broadcast sound. It was there even before stereo, certainly before 1059 as an FCC requirement. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 18, 20052005-07-18
"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message news:B6idnYHSROwJrkXfRVn-2w@comcast.com...> At about the same time the public was getting more interested in > better quality TV and especially better sound.Hmm... I'm not so sure... Faroudja was pushing his so-called "super NTSC" some 20+ years ago already, and it never caught on, despite the fact that it would have remained compatible with "regular" NTSC receivers. As far as I can tell, even today the average consumer is often much more interested in picture size and brightness than in picture detail. I've been surprised just how well some of the image processing found in modern projector TVs with screens in the 60+" realm manage to do in terms of keeping the picture looking relatively "sharp" given the signal they have to work with. ---Joel Kolstad
Reply by ●July 18, 20052005-07-18
Joel Kolstad wrote:> "glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message > news:B6idnYHSROwJrkXfRVn-2w@comcast.com... > >>At about the same time the public was getting more interested in >>better quality TV and especially better sound. > > > Hmm... I'm not so sure... Faroudja was pushing his so-called "super NTSC" some > 20+ years ago already, and it never caught on, despite the fact that it would > have remained compatible with "regular" NTSC receivers. > > As far as I can tell, even today the average consumer is often much more > interested in picture size and brightness than in picture detail. I've been > surprised just how well some of the image processing found in modern projector > TVs with screens in the 60+" realm manage to do in terms of keeping the > picture looking relatively "sharp" given the signal they have to work with.Back when TV receivers needed manual fine tuning, few viewers bothered to use it. To promote its use, makers eventually put a separate fine-tuning capacitor for each channel, so that once tuned, it stayed that way. Since the carrier is tuned on a 6 dB/octave slope, fine tuning made a big difference. It could even create a negative image and unless intercarrier sound was implemented, being off tune would pass the vertical rate through to the audio. I would visit someone watching the tube, and automatically walk over to the set and adjust the tuning. (Presumptuous, I know. I was young.) My hosts kindly humored me, but usually sent a clear message: why bother? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 18, 20052005-07-18
Jerry Avins wrote:> glen herrmannsfeldt wrote: > >> Jerry Avins wrote: >> >> (snip) >> >>>>> Not really. If you have a single frequency and you know what it >>>>> is, then >>>>> you can do it. That's rather uninteresting. Think about what happens >>>>> when you start with a band of frequencies. For one thing, how >>>>> would you >>>>> multiply? >>>> >> >> >> Slightly different, but I have heard of optical systems with >> frequency multipliers, such as a red laser through a non-linear >> material and then separating the third harmonic of the source >> beam. That is to get short wavelengths where there aren't any >> laser materials. >> >> For a modulated source it would be more complicated, but it seems >> that it could still work. > > > Sure it works. That's what's behind heterodyning. The modulated signal > is, of course, narrow band at the original frequency. The intercarrier > TV sound carrier is at 4.5 MHz. I brought it out of one set into a > push-push diode frequency doubler (aka full-wave rectifier) and into > the retuned IF (10.7 MHz to 9) of a broadcast FM tuner. Listeners were > surprised to hear how good the actually broadcast sound was. In > service like that, the intermodulation products are easily removed by > minimally selective filters.I believe the world's first colour TV where the only thermionic device was the picture tube was the Thorn 2000 (sold and rented under various names). This had a class D amp capable of very good results. You didn't need to mess around with an external IF and audio amp. If you just disconnected the internal speaker and connected a good external one is sounded pretty good. The current fad for class D amps as the shiny new way to get the size of home theatre boxes down amuses me. They seem to be nearly 40 years late. :-) Regards, Steve
Reply by ●July 19, 20052005-07-19
Steve Underwood wrote:> I believe the world's first colour TV where the only thermionic device > was the picture tube was the Thorn 2000 (sold and rented under various > names). This had a class D amp capable of very good results. You didn't > need to mess around with an external IF and audio amp. If you just > disconnected the internal speaker and connected a good external one is > sounded pretty good. > > The current fad for class D amps as the shiny new way to get the size of > home theatre boxes down amuses me. They seem to be nearly 40 years late. :-) > > Regards, > SteveWow. The Thorn 2000. What an addled youth I had working on those beasts. The sound was the least of the problems there. It also had as I remember, the first Switch Mode PSU with the PSU and the line oscillator forming and integrated unit, discrete transistor PAL decoder and a colour convergence board almost as big as the CRT. Those were the days. I can also sympathise with Jerry's tweaking propensity as I worked for a company who imported TVs from Germany to Ireland and my job then was to re-tune the sound I.F. from 5.5MHz to 6MHz and re-align the PAL decoders etc. I fondly remember that despite the excellent level of elegance in the German design, I had to add a hand wound coil to the collector of the video amp to 'square up' the teletext pulses. I digress... Dave.
Reply by ●July 20, 20052005-07-20
Joel Kolstad wrote: (snip)> Hmm... I'm not so sure... Faroudja was pushing his so-called "super NTSC" some > 20+ years ago already, and it never caught on, despite the fact that it would > have remained compatible with "regular" NTSC receivers.I am not sure what super NTSC is, but only relatively recently did anyone build a proper NTSC demodulator. NTSC, as designed in 1954, uses two chroma signals called I and Q, which don't correspond to R, G, or B but linear combinations of them. I has more bandwidth than Q, as the eye has more spatial resolution for those colors. The color burst, though, is phased to make it easy to decode along the R and B axis, ignoring the extra resolution. About the time that HDTV started to get interesting, some made EDTV receivers which could finally decode this information, about 40 years after it was added to the standard.> As far as I can tell, even today the average consumer is often much more > interested in picture size and brightness than in picture detail. I've been > surprised just how well some of the image processing found in modern projector > TVs with screens in the 60+" realm manage to do in terms of keeping the > picture looking relatively "sharp" given the signal they have to work with.-- glen
