Comments on: A PORTABLE COLOR RECORDER

By: Casandro

Casandro — Mon, 15 Dec 2008 15:13:40 +0000

Mike, what country was that?

Well today just doing it via a computerized system is _way_ cheaper. You can get full HD camcorders for less than 200 Euros.

By: Mike

Mike — Mon, 15 Dec 2008 12:35:13 +0000

Casandro, I don’t know if I want to laugh at your post. I had a friend/co-worker who worked at a station like that, and it wasn’t professional grade VHS or even consumer SVHS, it was off the shelf VHS. That was maybe 15 years ago, I would hope some of those stations have upgraded or have some sort of DVR set up by now if they are still around.

By: Casandro

Casandro — Mon, 15 Dec 2008 06:10:11 +0000

Hmm, with 450ips and 2 channels, something which you might potentially be able hack your audio tape machine to do, you’d get 2.4 MHz of bandwidth. That would be enought for decent video. I’ve seen worse on broadcast television. Seriously there are stations out there still using VHS for broadcast, because they never could afford more and cannot afford to switch to computer based editing.

By: Rick Auricchio

Rick Auricchio — Mon, 15 Dec 2008 00:30:55 +0000

Maybe it was 450ips?

By: Casandro

Casandro — Sun, 14 Dec 2008 20:18:45 +0000

Yes, but that’s cheating, it wasn’t a full resolution VTR.

By: JMyint

JMyint — Sun, 14 Dec 2008 20:09:51 +0000

Cassandro, I suppose you had never heard of the Fisher-Price PXL 2000.

http://www.retrothing.com/2005.....e_pxl.html

Thirteen minutes of video on a ninety minute audio tape isn’t too bad I guess, thats only 7 times speed.

By: Casandro

Casandro — Sun, 14 Dec 2008 19:40:13 +0000

Homebrew linear-scan VTRs sound interresting, but those 150 ips sound a little bit low. It’s just 20 times higher than normal audio tape. So if you estimate a Bandwidth of 20 kHz for the tape (unrealistically high) you’d only get 200 kHz for video. That’s still to low for a propper picture. You’d have to combine 10 channels to get the bandwidth needed for a decent picture. So unless you build special heads a home brew linear scan VTR might be very difficult.

By: Rick Auricchio

Rick Auricchio — Sun, 14 Dec 2008 19:06:58 +0000

Charlie, this article reminds me of a Popular Electronics article where you could build your own linear-scan VTR. Because of the high frequencies needed for TV, that deck ran at something like 150 ips (consumer audio tape runs at 7.5ips). It flew through a reel of tape in perhaps 10 minutes.

I used to be an avid “PopTronics” reader in high school, after having read a lot of the 50s-60s PopSci mags. My dad and uncle used to read PopSci, but it was I who went for the electronics end of things.

By: Casandro

Casandro — Sat, 13 Dec 2008 21:27:51 +0000

This sure was a _lot_ cheaper than the usual timebase correctors they had for colour video back then.

For you non-video geeks out there, essentially the problem is like this:
NTSC can be seen as simmilar to time-multiplexing of the colour components. So you transmit one component, then the other, then the first again (negative) then the second again (negative).
Under normal circumstances, the reciever will get a short colour burst at the start of every line. This burst should be enought to keep the “clock” of the reciever in sync with the one at the transmitter. If you have a VTR however imperfections in the mechanics can cause yitter which is easily large enought to cause completely false colours. In professional machines (mentioned in this article) you had to have a special electronic memory which can delay the signal by a varying amount of time. (done with varicap diodes and inductivities) It is set so it corrects the yitter from the mechanics. What they did here is to add a second signal at a low frequency from which you could derive the right yitterey clock to your yittery colour signal thus you can decode it again.

By: Charlene

Charlene — Sat, 13 Dec 2008 20:04:02 +0000

I seem to remember similar machines at our school. I can’t remember exactly when they were used, but by 1978 they were long gone, replaced either by actual film or by videotapes.

PS. Your Fig 8 turned into Fig. Smiley. Apparently 8 ) without the space gives you a smiley wearing sunglasses. It’s a cool schematic and everything, but I thought you’d appreciate the heads-up.