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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 11th Jan 2017, 3:26 am   #1
suebutcher
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Default 405 to 625

Is there a way to electronically covert a 405 line signal from a Sony VTR to 625line without expensive custom-made gear? This question was asked a couple of years ago, but the thread went nowhere. It's a practical question; there's currently a collection of off-air 405-line recordings of missing programmes that may disappear into limbo unless potential buyers know that the contents of the tapes can be saved to a digital format.
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Old 11th Jan 2017, 8:34 am   #2
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Default Re: 405 to 625

Yes, and not only that. Private off-air collections amassed in the 80s and 90s (on 405 U-matic and VHS in my case) would be much more convenient to view if they could be combined with my 'main system'.

Having said that, I suspect the amount of technical effort needed will ensure that this remains a blind alley.
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Old 11th Jan 2017, 8:44 am   #3
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Default Re: 405 to 625

If you could only somehow get an uncompressed, 6M samples/sec (!) .wav file of the 405-line video, the rest of the process is stuff you can almost do at your leisure. (Playing the raw PCM out via a suitably-fast D-A converter would work, but you probably want to compress it to a standard format in practice.)
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Old 11th Jan 2017, 10:32 am   #4
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Default Re: 405 to 625

There's always the quick-and-dirty approach - a 405-line monitor with a 625-line camera pointing at it. Or, these days, an HD camera, which could hopefully capture the 405-line images with enough resolution to avoid losing any detail due to inter-line aliasing or similar.

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Old 11th Jan 2017, 11:27 am   #5
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Default Re: 405 to 625

Quote:
Originally Posted by julie_m View Post
If you could only somehow get an uncompressed, 6M samples/sec (!) .wav file of the 405-line video, the rest of the process is stuff you can almost do at your leisure. (Playing the raw PCM out via a suitably-fast D-A converter would work, but you probably want to compress it to a standard format in practice.)
I'd thought of that myself, digitally capturing the raw waveform somehow and not bothering with standards conversion until it's convenient. How about splitting the 2 MHz bandwidth video signal into, say, forty channels frequency-shifted down to 0-50kHz, and sampling them? Could equipment designed for music recording be modified to do this?

Optical conversion is too poor in quality to be considered properly saving the material. The best option at the moment is to copy the recording to Umatic tape until a converter becomes available.
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Old 11th Jan 2017, 3:23 pm   #6
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Default Re: 405 to 625

Have you tried contacting Darryl of Aurora fame? He may be able to help though will undoubtedly want paying (quite rightly too!). I wouldn't be surprised if he could make a custom Aurora that would do the job. If not I could put it on my roundtuits pile as an FPGA project.
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Old 11th Jan 2017, 3:31 pm   #7
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Default Re: 405 to 625

Would a video capture card linked to VLC work?
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Old 12th Jan 2017, 1:02 pm   #8
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Default Re: 405 to 625

I really don't know much about video capture. Does the first stage of sampling run free, or is it synchronised to a particular television system?
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Old 13th Jan 2017, 1:42 am   #9
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Default Re: 405 to 625

Perhaps an optical method is not completely out of the question. Some years ago I experimented with filming the face-plates of 14" TV monitors with a video camera. The video camera was gen-lockable to vertical sync so, there was no vertical rate drift between the source signal and the cameras video out. When the monitor was set up properly for contrast & brightness and the camera adjusted as best possible, the result was surprisingly good. This sort of thing obviously will be nowhere near is as good as an electronic converter or digital capture, but it is a possible way to get some sort of copy of the material into another format. And since the 405 and 625 vertical rate is the same, it is an easier task than trying to go between PAL & NTSC this way.
It is interesting that a lot of "copy DVD's" are made by people filming the movie screen with a digital camera and they expect to pass that off as as reasonable copy !
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Old 13th Jan 2017, 5:29 pm   #10
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Default Re: 405 to 625

When we were in France for the 1999 Eclipse, I got very acceptable recordings from French TV (SECAM) by pointing my PAL VHS-C camcorder at my brother-in-law's TV screen. I had to turn the camcorder off and on a few times to get the camera synched with the TV so that no line was visible part-way down the screen, but once set up, synch was maintained for the 30 mins or so I was recording. Synch was maintained while the camcorder was paused. The TV was a 15" Schneider. It was simple to test for synch by panning the camera sideways with a jerk (it was mounted on a tripod with a pan and tilt head), when tearing of the picture part way down the screen was apparent in the camcorder's viewfinder in the non-synch state. It was necessary to adjust the exposure to 1/50 sec, something that seems to be lacking in current models of consumer camcorders.
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Old 16th Jan 2017, 5:59 am   #11
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Default Re: 405 to 625

Optical conversion from 405 to 625 lines might present more problems than those of simply recording a 625/50 picture from a 625/50 monitor.

At least that is the impression that one gets from the attached Wireless World 1953 June article, which describes what was probably the first professional 405-to-625 conversion apparatus, developed by Philips. For example, spot-wobble on the 405-line monitor would seem to be a requirement.

I wonder whether any broadcasting organizations ever did 405-to-625 conversions electronically? By the time that electronic conversion became a reality, the daily requirement was more the other way around, namely 625-to-405. (Although I imagine that 625-to-819 was required in France.) If not, then maybe not much work has been done anywhere on the 405-to-625 electronic conversion case.

Regarding digital storage without initial standards conversion, what happens if a 405 baseband video signal is fed into a PAL 625 DVD recorder. Something I have discovered is that when an NTSC 525 video baseband signal is fed into a single-region PAL 625 DVD recorder, it can be recorded, and then plays back as a vertically shortened picture, occupying about the top 80% of the screen, with below it a black band populated by white horizontal bars. It looks though as if all of the picture information has been retained. Still, then converting that back to the correct standard from the HDMI output might be a more complicated affair than initial conversion. So maybe a 405-line input would be treated somewhat similarly.


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Old 16th Jan 2017, 2:57 pm   #12
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Default Re: 405 to 625

Quote:
Originally Posted by Synchrodyne View Post
For example, spot-wobble on the 405-line monitor would seem to be a requirement.
To some extent the need for that depends on the size of the CRT & image and the focused beam size. One fix rather than to make a spot wobbler is to simply reduce the height and width of the image until the focused CRT's beam diameter is such that the lines just join.
So for a 405 line image, I would start with a common garden monochrome 9 inch standard video monitor (which are cheap to obtain, like those commonly used in the CCTV industry) and modify it for 405 lines, then, if required, reduce the height/width so that the gap between the scanning lines just vanish before making a video of that image. Or someone might already have a small face 405 line monitor/TV.
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Old 16th Jan 2017, 3:28 pm   #13
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Default Re: 405 to 625

Quote:
Originally Posted by Argus25 View Post
To some extent the need for that depends on the size of the CRT & image and the focused beam size. One fix rather than to make a spot wobbler is to simply reduce the height and width of the image until the focused CRT's beam diameter is such that the lines just join.
By doing that, wouldn't you potentially lose some of the horizontal definition? The full definition previously provided by a given size of spot (which would remain constant) might be blurred by crunching in the picture horizontally.

If spot wobble isn't on the cards, I'd keep the picture size the same and use a vertically elliptical (astigmatic) spot.

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Old 17th Jan 2017, 4:36 am   #14
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Default Re: 405 to 625

Quote:
Originally Posted by Panrock View Post
By doing that, wouldn't you potentially lose some of the horizontal definition? The full definition previously provided by a given size of spot (which would remain constant) might be blurred by crunching in the picture horizontally.
Possibly some of the H resolution could be lost, depending on what was present in the source material. At the point that the spaces between the lines just vanish, then there would be about 377 active picture elements vertically, then about 377 x 4/3 elements possible horizontally. The H resolution supported by the crt under this condition is still more than for the V.
I think in the past I calculated the effective upper video frequency supported by this scenario and it was roughly about 2.5MHz for a 405 line system. The 405 line source material might only be any good for that anyway. So it is all compromises and it would be an imperfect way to transfer/convert the video, but it is a way.
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Old 17th Jan 2017, 10:04 pm   #15
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Default Re: 405 to 625

I could have also mentioned that if the camera's video out and the image has gone a bit soft looking, at least its easily possible to sharpen it up a bit with a simple & cheap video accessory box with an aperture correction (high frequency) control before it is recorded for the first dub. The process might work better with a 1970's vintage B&W video camera based on a vidicon tube or similar because the image lag provides some flicker filtering, rather than a new digital camera, but I'm not 100% sure about this because the only cameras I have tried for this purpose in the past were tube based.

Also on the H resolution issue where the picture elements are touching vertically, this is discussed and calculated on page 266 Practical Television 1955 November: The corresponding bandwidth is 2.4MHz. This is still a reasonably crisp image on a small sized raster. And in practice, due to the focused spot size in the crt, a suitable tube/monitor could be a 5 or 6" tube. So a typical small B&W industrial monitor, modified to 405 lines could be used and the CRT focus just fractionally off until the lines just touch, if they were not touching already.That monitor could be built into a housing with the camera to make a fairly compact 405-625 converter unit.

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Old 2nd Feb 2017, 10:57 pm   #16
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Default Re: 405 to 625

There is a concurrent discussion of this matter here: http://golbornevintageradio.co.uk/fo...d.php?tid=6153 including some thoughts on initial digital capture followed by later software conversion.

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Old 10th Feb 2017, 11:09 pm   #17
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Default Re: 405 to 625

Having just noticed this thread, it seems to me this would be a pretty easy job with a microcontroller. Back of a fag packet wise, each field is about 200x540 pixels (matching vertical and horizontal resolutions, interlaced) which is a bit over 100k, so 200k for a full frame.

The big problem with interlaced signals is always the resampling, because half the information is missing on each field so you get combing when you combine them, and none of the interpolation methods are perfect.

But you could probably fit the circuit in a matchbox, kind of thing.
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Old 11th Feb 2017, 1:35 am   #18
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Default Re: 405 to 625

What is the bandwidth of a 405 line video signal?
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Old 11th Feb 2017, 2:15 am   #19
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Default Re: 405 to 625

3 MHz as broadcast, but I'd guess something less, maybe around 2 MHz or so, as stored on -inch or -inch videotape.

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