Mechanical video recorder

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Re: Mechanical video recorder

Postby Steve Anderson » Thu Oct 03, 2019 1:37 pm

Both Karen Orton and Chris Lewis have had varying degrees of success using Compact Cassettes. They both had an analogue 'processor' to make corrections to the shortcomings of this medium....time to dig through all those newsletters...

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Re: Mechanical video recorder

Postby Harry Dalek » Thu Oct 03, 2019 11:59 pm

Klaas Robers wrote:Harry,

before you are going to try to record NBTV, first try to record a square wave signal. If you listen at the replay, you hear almost the same sound as when you listen at the original wave form. But if you look at your oscilloscope to the replay signal, you will not recognize the square wave of the input signal.
This happens because the lower frequencies are recorded deeper in the tape and at some distance from the gap in the recording head. The higher frequencies are recorded on the surface of the tape and right under the gap. What you will see is that the recorded square wave plays back as a more or less triangle wave.


Oh Klaas that's a big change to the waveform i will give that a go ,I did think the sync sounded like the problem but didn't think it was a change of waveform more thinking more its was a weak sync pulse .
That's a good experiment i will do tomorrow and have a look at the results on the scope it was something i planned to do for the cd mechanical recorder a while back but other problems took my time up and never got around to it ...

As our ears are not sensitive to wave forms, but sensitive to the volume (strength) of higher and lower sine waves, we do not hear this type of distortion. SSTV is much less sensitive to this, because it is an FM tone. All frequencies are close to each other, 1500 Hz to 2300 Hz, in the audio spectrum. So all tones are recorded at almost the same depth in the tape and at almost the same distance from the gap in the recording head.


Yes not really a problem for tape magnetic recording as you say but harder for record for a record but some thing must still be there as it can be detected by my android phone sstv app least one of its sections .

This distortion is deadly for NBTV video signals. That is the reason that all video tape recorders work with a FM subcarrier, just like SSTV.


Oh i see ...i found the one time i tried it interesting as i was expecting it to work ..i was surprised it didn't...i looked into it just to see if i would get the same result as from the mechanical CD recorder not expecting the same ...well now i know ...good to know !

But do not stop your experiments.! Go on with it, because only if you see it yourself, you are convinced and you learnt from it for life time.


I will go on with it the recording work it is something new to me and interesting to solve the problems ...the slight sstv i managed to record and play back does give me hope things can only get better ,your advice is a big help in working in the right direction Thanks Klaas.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Mechanical video recorder

Postby Harry Dalek » Fri Oct 04, 2019 12:10 am

Steve Anderson wrote:Both Karen Orton and Chris Lewis have had varying degrees of success using Compact Cassettes. They both had an analogue 'processor' to make corrections to the shortcomings of this medium....time to dig through all those newsletters...

Steve a.


OH yes if any one put their mind to it Karen would be the one to get it working !
I will have a look if i have any issues with Chris L and Karen's work on this ...i also keep forgetting i have issues coming in my emails !arrr that reminds me now .
Have to say as i mentioned to Klaas i was just expecting this would work as is and never bother ever to see ..getting off my bottom i can see it does not but if i can get it working it would help on the mechanical embossing on the CD recording ...problem here is i can't reused a mistake on a mini record but can on a tape mistakes are less of a issue since to can tape over mistakes .
Thanks also Steve !
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Re: Mechanical video recorder

Postby Harry Dalek » Fri Oct 04, 2019 1:21 pm

Today got off my bottom and hooked up and recorded and viewed some waveform recordings

Below 400 hz on the cassette recorder top input 400 Hz square wave bottom recorded distorted waveform recording as Klaas mentioned
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Next i would see how bad a NBTV reversing wave grey bars video would look via the cassette recording top again input bottom the cassette recording ...all i can say is dear me and that was the best result and the wave form

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Next i tried something i would of thought would work i swapped over to a VCR and recorded via the Audio heads a little different result to the cassette recorder but still not usable well at least on a software monitor i would also expect a bad result on an analog monitor .
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I can see its not just the sync pulse but with a clean pulse it might give a cleaner waveform to the video part of it ...
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Re: Mechanical video recorder

Postby Harry Dalek » Sat Oct 05, 2019 12:21 pm

Just putting it out there i have not just swapped over to Tape from Record recording i am using it as a tool to see if there are any similar problems ideas i can use when i go back to it .
I should just hook up the tape deck to the Binocular monitor and have a look how well a monitor such as this copes with the poor waveform ...i only really ever tied record and tape NBTV recording to software monitor .
Taking Steve's Advice i have been reading past club news Letters.
What i have found is swapping of audio nbtv tapes was pretty common Gill miles and Allan Short did it all the time many due to the monitors were analog .
Results were viewable but help such as improving lengthening the the sync pulse helped.
Then i found that Jermey Jago over came the problem Klaas mentioned in a past post of the audio head recording the bandwidth of the Frequencies to different layers of the Audio tape which plays hell on waveform on play back .
He's idea was to AM modulate the the video on to a 10khz carrier record that and have a demodulator on the output before the monitor .
Below a passive version similar mentioned in the newsletters also a active version first used on the first version
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My first thoughts were just either make the lengthier sync pulse record that or reinsert it after but still are the other problems making it useless for any software monitor so Jermey's idea does sound the way to go for Tape anyway not to complex .

I suppose its similar to the pulse width modulation in some way for laser modulation we have used in the past .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Mr Ferdinanc Plew

Postby Harry Dalek » Sun Oct 06, 2019 8:55 pm

Mr Ferdinanc Plew With The Television Set And Television Gramophone He Has Designed.1934
Interesting there could not of been many making phonovision type players wonder if it was a lathe as well ?
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Mechanical video recorder

Postby Klaas Robers » Tue Oct 08, 2019 6:38 pm

Harrt, the sound on a VCR is recorded in exactly the same way as the sound on a cassettte recorder. So the distortion is similar. The VCR-tape is very thin, so there is not so much depth in the magnetic layer. But also for compact cassettes the tape is thin, in order to get enough playing time.

The video in a VCR is recorded as an FM-subcarrier of a frequency of several MHz and by a separate recording head on a fast rotating disc.
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Re: Mechanical video recorder

Postby Harry Dalek » Wed Oct 09, 2019 4:57 pm

Klaas Robers wrote:Harrt, the sound on a VCR is recorded in exactly the same way as the sound on a cassettte recorder. So the distortion is similar. The VCR-tape is very thin, so there is not so much depth in the magnetic layer. But also for compact cassettes the tape is thin, in order to get enough playing time.

The video in a VCR is recorded as an FM-subcarrier of a frequency of several MHz and by a separate recording head on a fast rotating disc.


Thanks for your interest here Klass before i started looking into this i was thinking it was more a correct speed problem so thinking the VCR would be the most accurate magnetic recorder ...your input has shown me this is not the problem ...
Out of interest is the reel to reel the same you think ? as it using thicker tapes ?
I would think the VCR video heads would be useless for low audio what would you think would be the lowest video system it could record ? i have heard soem vcrs managed 405 line .
Well back to the cassette tape i am going to have a look what NBTV it looks like on my binocular NBTV monitor if it can play it you may know tapes seemed to be the thing in the past for NBTV so must be possible ...also having a look at the reversing wave on the record lathe the staircase is very easy to see how good or poor the result is even if it does not play ...i tried recording a 400 hz tone bit wobbly does not take much to change the record speed depending on how deep the lathe embosses the recording.. ideally its best to do it fine but a stylus will not pick the groves if so ,so a catch 22 at times correct speed or correct embossing track .. i would rather just see for now what the video waveform looks like best i can record it ...if time tomorrow i will post up some results .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Mechanical video recorder

Postby Andrew Davie » Wed Oct 09, 2019 5:08 pm

Just a thought: What if you were recording onto a hot medium... would it have an easier time embossing the track?
In other words, heat up the CD in the oven for a minute or so before recording. Well who knows... something to try!
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Re: Mechanical video recorder

Postby Steve Anderson » Wed Oct 09, 2019 6:35 pm

Harry Dalek wrote:I would think the VCR video heads would be useless for low audio what would you think would be the lowest video system it could record ? i have heard soem vcrs managed 405 line .


A 625 VCR should record and playback 405 monochrome no problem, the field and frame rate are the same as 625. There's no colour so that part of the VCR should simply shut down. The field/frame rate is what the capstan and drum servos lock to, the line rate doesn't matter...except - if it has a TBC (Time Base Corrector). Few VCR's had that luxury and it can usually be switched off or bypassed anyway.

IF (a real IF these days) you can get a S-VHS (Super VHS) machine and the S-VHS tapes, these have a greater luminance bandwidth ideal for 405 recording.

Wiki...S-VHS improves luminance (luma) resolution by increasing luminance bandwidth.[2] Increased bandwidth is possible because of increased luminance carrier from 3.4 megahertz (MHz) to 5.4 MHz.[2] Increased luminance bandwidth produces a 60% improvement in (luminance) picture detail, or a horizontal resolution of 420 vertical lines per picture height – versus VHS's 240 lines.

The result is that it's hard to tell the difference between the original 405 and the S-VHS copy.

Really, if you keep the field rate at 50Hz (60Hz US etc..), the VCR doesn't care what the signal information is as long as it's pseudo-video in nature. This applies to standard VHS too, just keep the info within the limits of the format...

Steve A.

The little white wobbly'blob' at the bottom of the screen (not always visible, the head-switching moment) might appear to be wider than in 625 material...it varies so I'm told.
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Re: Mechanical video recorder

Postby Harry Dalek » Wed Oct 09, 2019 8:17 pm

Andrew Davie wrote:Just a thought: What if you were recording onto a hot medium... would it have an easier time embossing the track?
In other words, heat up the CD in the oven for a minute or so before recording. Well who knows... something to try!


Hi Andrew i have heard of that some use a hairdryer or heat gun or heated up stylus this would be easier to do with an induction coil if using the needle idea to record i am using a gem stylus of some sort still .

So yes your idea of heating before or during embossing is correct

I tried before using oil or some sort of lubricant that works well cuts down noise and i suppose fiction ...should call it fiction recording !

At the moment i am using a little magnet and a nut for correct weight for pushing down the record stylus as you can see in the photo even the movement along top closer or further along the stylus can effect the cut or emboss of the track ...lots and lots of factors in this type of recording :roll:
BTW thats a 400 hz recording on the scope play back from the other record player it should be a square wave .
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Mechanical video recorder

Postby Harry Dalek » Wed Oct 09, 2019 8:35 pm

Steve Anderson wrote:A 625 VCR should record and playback 405 monochrome no problem, the field and frame rate are the same as 625. There's no colour so that part of the VCR should simply shut down. The field/frame rate is what the capstan and drum servos lock to, the line rate doesn't matter...except - if it has a TBC (Time Base Corrector). Few VCR's had that luxury and it can usually be switched off or bypassed anyway.


i have 2 SP professional VHS machines have to have a look what extras it has to adjust things .

IF (a real IF these days) you can get a S-VHS (Super VHS) machine and the S-VHS tapes, these have a greater luminance bandwidth ideal for 405 recording.


These might be super VHS but only have SP speed and speed control as i recall on play back

Wiki...S-VHS improves luminance (luma) resolution by increasing luminance bandwidth.[2] Increased bandwidth is possible because of increased luminance carrier from 3.4 megahertz (MHz) to 5.4 MHz.[2] Increased luminance bandwidth produces a 60% improvement in (luminance) picture detail, or a horizontal resolution of 420 vertical lines per picture height – versus VHS's 240 lines.

The result is that it's hard to tell the difference between the original 405 and the S-VHS copy.


I also have a Sony Umatic machine quality must be up there with VHS ..but its interesting to me 405 line is fine on VHS

Really, if you keep the field rate at 50Hz (60Hz US etc..), the VCR doesn't care what the signal information is as long as it's pseudo-video in nature. This applies to standard VHS too, just keep the info within the limits of the format...


I Always wanted to try the and its still on the to do list test the flying spot PMT camera for a record for higher line rates it can do ..get around to it ! arrr

Steve A.

The little white wobbly'blob' at the bottom of the screen (not always visible, the head-switching moment) might appear to be wider than in 625 material...it varies so I'm told.


I have to keep an eye out for that thats new to me .
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Re: Mechanical video recorder

Postby Klaas Robers » Wed Oct 09, 2019 9:13 pm

Recording a square wave of about 200 Hz is a good test to see how the recording - play-back channel behaves. In the far past I did these type of tests on professional studio-type reel to reel recorders, also on 19 cm/sec and 38 cm/sec, and the result was invariably that the output did no more look like a square wave. The audio recording process with HF bias magnetisation is the source of the distortion. But with no HF bias magnetisation the distortion is even worse!

But doing experiments in this direction is very valuably. I have seen that Karen did this too with cassette recording a few years ago and wrote about it in the Newsletter of the NBTVA. Read that stuff. And do the square wave experiments with your lathe as well.
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Re: Mechanical video recorder

Postby Steve Anderson » Thu Oct 10, 2019 4:17 pm

Klaas Robers wrote:...And do the square wave experiments with your lathe as well.


Here would be a fine opportunity for Albert to have his say with his experience of the cylinder recorders/players he constructed...

His method was a helix on a 3D cylinder, whereas here it's a spiral on a 2D surface. The cylinder has the advantage of 'constant linear velocity'. If you can see a CD while playing it starts at a high RPM and slows down as the recording nears the end. (A lot of portable CD players had a window you could see the disc spinning through, also a CD plays from the inside to the outside, opposite to a pressed record). I presume the same is true of DVDs and the like.

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Re: Mechanical video recorder

Postby Harry Dalek » Thu Oct 10, 2019 5:09 pm

Klaas Robers wrote:Recording a square wave of about 200 Hz is a good test to see how the recording - play-back channel behaves. In the far past I did these type of tests on professional studio-type reel to reel recorders, also on 19 cm/sec and 38 cm/sec, and the result was invariably that the output did no more look like a square wave. The audio recording process with HF bias magnetisation is the source of the distortion. But with no HF bias magnetisation the distortion is even worse!

But doing experiments in this direction is very valuably. I have seen that Karen did this too with cassette recording a few years ago and wrote about it in the Newsletter of the NBTVA. Read that stuff. And do the square wave experiments with your lathe as well.


I do have 2 reel to reel recorders which i saved from here and there but yet to Test them ! as i get older i seem to have more time to try things out ..so another on the to do list i think i might be lacking a empty reel for the odd tapes i have to wind onto ..have to see if i ended up finding one or not .

Testing a lower frequency it should get closer looking to a square wave i think as the effect looking on my scope higher the frequency to the limits of what my scope can do the square wave starts to look more like a back sine wave so i understand its a bit like whats happening here on mechanical recording ...

I have been reading up on others past experiments good to learn from others experiments ... in the early days of the NBTV cassette Tapes were used a bit but not really explained if they did any thing to the video before record ... i would think lengthening of the sync pulse before record might of helped as explained latter on for early tape recording NBTV.
Karen has some good ideas on the record on tape problems ,i feel reading what i have modulating the video on a HF carrier and recording that and demodulating it is the way to go .

I still not perfect but easiest approach...I did today do a few tests from cassette recorded NBTV to binocular monitor the sync plays hell with the monitor but at times there is video displayed .

I noticed since i my cassette player has play back speed adjustment the speed is not that much of a problem if its off i am seeing more as you have explained to me its getting that bandwidth of frequencies from the video to record on the tape or Record so i am moving more looking into this or ways around it ...

I tried a record of the staircase reversing wave on the record but best i can see is the stair case for the grey scale levels are gone more a bad sawtooth and no sync i could see at all but i am recording at very low levels out of the lap top to get higher frequencies takes more amplifying so i think this is more of the problem for that to be fixed at the moment ..i will post some pic's up after i reply to the posts today .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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