mrapple@quack.sac.ca.us (Nick Sayer) (06/24/91)
(Yes, I'm full of questions lately) Let's say I want to build a cable ready, Stereo/MTS television demodulator (i.e. the VCR without the VCR that we've all been talking about lately). Fine. I need to build a frequency generator to generate a frequency suitable to mix with the RF to get to the first IF of 45 MHz. From there, Motorola makes a pair of chips to do IF amplification and TV decoding. Fine. The FM subcarrier would, theoretically, be available at 50.75 MHz (or so). Fine again. Now the MTS part. How does MTS work? Is it similar to FM broadcast stereo ( DSB no carrier L-R at x kHz and pilot at x/2 kHz ) ? I don't think so or at least if so, x is not 38 kHz, since channel six here has stereo+SAP, but doesn't register on my stereo (which tunes that low). So how does it work, and does anyone have any chips to do this? Has Radio Electronics done this yet? I'd think the demand would be large enough for them to take a crack at it. -- Nick Sayer | Official Scapegoat for the | "And now my mrapple@quack.sac.ca.us | MC68HC11 Mailing List. | post is done!" N6QQQ | To subscribe, send mail to | --buster@acme.edu 209-952-5347 (Telebit) | mc68hc11-request@quack.sac.ca.us |
bender@oobleck.Eng.Sun.COM (memory fault - core dumped) (06/24/91)
In article <kXAYtXS@quack.sac.ca.us> mrapple@quack.sac.ca.us (Nick Sayer) writes:
->Let's say I want to build a cable ready, Stereo/MTS television demodulator
->(i.e. the VCR without the VCR that we've all been talking about lately).
->Fine. I need to build a frequency generator to generate a frequency
->suitable to mix with the RF to get to the first IF of 45 MHz. From
->there, Motorola makes a pair of chips to do IF amplification and TV
->decoding. Fine. The FM subcarrier would, theoretically, be available
->at 50.75 MHz (or so). Fine again. Now the MTS part. How does MTS work?
->Is it similar to FM broadcast stereo ( DSB no carrier L-R at x kHz and
->pilot at x/2 kHz ) ? I don't think so or at least if so, x is not
->38 kHz, since channel six here has stereo+SAP, but doesn't register
->on my stereo (which tunes that low). So how does it work, and does
->anyone have any chips to do this? Has Radio Electronics done this yet?
->I'd think the demand would be large enough for them to take a crack
->at it.
Of course, you could also go to surplus stores/sales, pawn shops, garage
sales, etc... and pick up a non-working MTS VCR, pull the tuner and
possibily power supply out of it and put the stuff in a box...
mike
--
------------------------------------------------------------------------
1985 Honda Shadow VT1100 | DOD #000007
1989 Honda NX-650 | AMA #511250luns@spocom.guild.org (Luns Tee) (06/24/91)
mrapple@quack.sac.ca.us (Nick Sayer) writes: > at 50.75 MHz (or so). Fine again. Now the MTS part. How does MTS work? > Is it similar to FM broadcast stereo ( DSB no carrier L-R at x kHz and > pilot at x/2 kHz ) ? I don't think so or at least if so, x is not Yep. x is 31.5 Khz rather than the 38 Khz of broadcast. Take half of that and tell me if it looks familiar. (31.5 actually, isn't exact) That the pilot is the horizontal scanning frequency was used in some suppresed-sync scrambling schemes.
mzenier@polari.UUCP (Mark Zenier) (06/25/91)
In article <kXAYtXS@quack.sac.ca.us> mrapple@quack.sac.ca.us (Nick Sayer) writes: >Let's say I want to build a cable ready, Stereo/MTS television demodulator >(i.e. the VCR without the VCR that we've all been talking about lately). >Fine. >Fine again. Now the MTS part. How does MTS work? >Is it similar to FM broadcast stereo ( DSB no carrier L-R at x kHz and >pilot at x/2 kHz ) ? Yes, X = 2 * horizontal scan rate ( 15734 * 2 ) >So how does it work, and does >anyone have any chips to do this? Has Radio Electronics done this yet? Yes again, about 4 or 5 years ago. One trick is that some of the signal (the L-R ?) is processed through some sort of Dolby noise recduction that is patented, which the RE project did not do. Mark Zenier markz@ssc.uucp mzenier@polari.uucp
csmith@plains.NoDak.edu (Carl Smith) (06/25/91)
In article <4561@polari.UUCP> mzenier@polari.UUCP (Mark Zenier) writes: [some discussion of MTS stereo TV sound deleted] >>So how does it work, and does >>anyone have any chips to do this? Has Radio Electronics done this yet? >Yes again, about 4 or 5 years ago. One trick is that some of the signal >(the L-R ?) is processed through some sort of Dolby noise recduction that >is patented, which the RE project did not do. >Mark Zenier markz@ssc.uucp mzenier@polari.uucp Actually it is dbx. Similar to dbx cassette players. The reason radio electronics did not include the dbx noise reduction is that it would be illegal, I think. I don't know the details, but dbx equipement must be licenced with the designers and manufacturers of dbx. You can get a licence, but then all you can do is buy dbx decoding chips and put them in your equipment. You can not sell the parts to the general public for their own use. Therefore there would be no way of the general public to get the dbx decoder parts, even if they did include it in the project. They did include some replacement circuitry that came close to performing the function of the dbx chips, but it wasn't near perfect. If they did include an exact replacement circuit for the dbx parts, they would probably be in trouble for patent infringements. So the only way to get TRUE MTS stereo TV is to buy a stereo TV or an and on stereo decoder box. BUT, if all you have is a poor sounding mono TV, the Radio Electronics project will still sound FAR better, even if it does not have the dbx circuitry and is not true MTS stereo. It is likely that most people will not hear the difference, and the ones that do won't hear much of a difference. It's hardly worth the trouble to build this project, since you can get a Recoton FRED III Stereo MTS decoder box from Damark Inc, for $39.99. It will either demodulate channel 3 audio, use the MPX output of your TV, if it has one, or will pick up the audio IF with a probe that you stick on the bottom of your TV. It will receive true dbx MTS stereo, SAP (second audio program), and has a 12 watt audio amp built in. You couldn't buy the parts for this and build it yourself for less than $39.99. ----------------------- Carl D. Smith Jr. csmith@plains.nodak.edu -----------------------