Jenkins Instructions to make a radiovisor

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Jenkins Instructions to make a radiovisor

Postby Harry Dalek » Fri Mar 04, 2022 7:24 pm

A lot NBTV relates to Baird's Mechanical Television where as there were others experimenting with Television Charles F Jenkins being another sharing this one off my web site for those interested
San Antonio Express
Location: San Antonio, Texas, United States Of America
Issue Date: September 2, 1928
San-Antonio-Express-Sep-02-1928-p-62 (1).pdf
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San-Antonio-Express-Sep-02-1928-p-62.Jpeg
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: Jenkins Instructions to make a radiovisor

Postby FlyMario » Sun May 22, 2022 7:58 am

Wow 48 holes. Can an audiotape even support that?
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Re: Jenkins Instructions to make a radiovisor

Postby Harry Dalek » Sat May 28, 2022 2:25 pm

FlyMario wrote:Wow 48 holes. Can an audiotape even support that?


Yes but i think the tape would have to speed the tape up, the first video recorders did not have a rotating video head just sped the tape past the head very quickly .
Steve .A ,mentioned you could record NBTV on a VCR have not tried it yet got the band width there .
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: Jenkins Instructions to make a radiovisor

Postby Steve Anderson » Sun May 29, 2022 1:31 pm

Yes, I did an item for the newsletter and the BATC's CQTV magazine many years ago using the video path of a VHS VCR to record NBTV. My aim was mainly to get a frequency response down to DC, but as a bonus I was able to extend the upper frequency limit too.

However, 48 line NBTV at a 12.5Hz frame rate isn't impossible on an audio tape recorder - but it sure needs to be a good one! Basically open-reel, not a cassette.

Say 48 lines with an aspect ratio of 3:2 would need around 72 pixels/line, but could be more or less.

A frame = 48 x 72 = 3,456 pixels (nice number!). At a 12.5Hz frame-rate = 43,200 pixels/sec. Or a bandwidth of 21.6kHz. Add say 10% for syncs etc.= 23.76kHz...I did say it had to be a good recorder! Probably a studio-quality machine running at 15ips/38.1cm/sec. If you apply a Kell factor [1] of (say) 0.8 that reduces the upper bound to 19kHz. Quite possible on a good quality machine, maybe even at 7.5ips/19.05cm/sec...but keep the recording level low-ish to avoid tape saturation.

A machine that runs at these speeds would probably be a good quality device and hopefully well maintained. That's the usual 'direct-to-tape' method.

The VHS machine/system Harry referred to is sampling the NBTV waveform at 31.25kHz, twice the 625 line rate and treating those analogue samples as part of an almost standard 625 video waveform. The biggest headache is the required 50Hz vertical information in this now 'pseudo-625' waveform. No 50Hz, no head-drum or capstan lock. Same applies to 525/60.

There still is/are the standard audio tracks available. Linear or Hi-Fi, mono or stereo if fitted available.

If I were to repeat the exercise today I would encode the NBTV digitally then insert that into the video waveform. That would negate the 50/60Hz vertical sync issue.

But not having a VCR anymore it's most unlikely I'd have a go at it...and these days there are better/easier ways to do the same...have a look at the thread, "Move-E-Stor MkI" for some ideas. This is still a 'work-in-progress' project...though updates maybe slow for a while until I get clear of a large 'real work' project. Plus I need still to buy a new version of Autocad, That's not an insignificant investment!!

Move-E-Stor MkI viewtopic.php?f=10&t=3116

Steve A.

[1] Kell factor. https://en.wikipedia.org/wiki/Kell_factor

The original item as it appeared in the BATC's 'CQTV' magazine November 2005....almost 17 years ago!! Though again, I would do it differently these days...

Proof 2.pdf
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However, any further development on this subject should really be posted in the 'Electronic NBTV' section rather than here...
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Re: Jenkins Instructions to make a radiovisor

Postby Harry Dalek » Mon May 30, 2022 4:25 pm

Very interesting was it ever built Steve by you or any one you know of ? if not what a pity i can see a lot of work went into that .
I will put this on my to do list :wink: , i can see the old VCR is very Vintage these days but most here like vintage electronics !
..no fun in little circuit boards so tiny made by robots making it impossible to copy even if you could .
Another one for the to do list in the back of my head is a wire recorder for NBTV as in stainless steel ,you can still buy the old wire recorder reels but they cost a bit ,i was looking into if you could buy thin stainless steel wire reels and the answer Yes to various thin gauge's of this type of wire...i always thought this would be a fun project when i get around to it ,having just done phonovision needed a brake and thus the 405 and various other 100ish to 405 line monitor project at the moment ,having now the PC to VGA early tv system modelines working silly not to give this a go ..give's me an excuse to make another monitor as well !
But getting off Track thanks for posting the PDF i didn't know this project of yours.
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: Jenkins Instructions to make a radiovisor

Postby Steve Anderson » Mon May 30, 2022 4:48 pm

Yes, it was built and worked as advertised, that's how I was able to get the few oscillographs in the article...though it was done on a breadboard, not a PCB or even Veroboard or stripboard. So it has no physical existence now.

Harry, (or anyone else), if you are serious in building this I'm OK with doing a modest redesign to hopefully make it a bit simpler and add in some improvements/refinements. Getting rid of all those monostables would be a good start! It was more a 'proof of concept' that it could be done.

The only 'niggle' I have is how many still have operational VCRs these days? Or whatever may have replaced it? If the 'replacement' uses some form of compression it may corrupt the signal. I would be interested in how people do the 'time-shifting' that the VCR was mostly used for then. If anyone still does that these days...with TV programs being as crap as they are these days, I would say few...

Although this would be an interesting 'retro' project I'm more inclined to stick with the 'Move-E-Stor' concept which uses easily obtainable components today.

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Re: Jenkins Instructions to make a radiovisor

Postby Dave Moll » Mon May 30, 2022 5:53 pm

Steve Anderson wrote:I would be interested in how people do the 'time-shifting' that the VCR was mostly used for then. If anyone still does that these days...with TV programs being as crap as they are these days, I would say few...


Mostly what I watch is the BBC, so I do most of my time-shifting of programmes by using their iPlayer online access to programmes rather than recording them.

Although I do have a combined VHS/DVD player/recorder, it ceased working a couple of years ago, so I no longer have the means to play my large collection of material on VHS cassettes either.
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Re: Jenkins Instructions to make a radiovisor

Postby Steve Anderson » Tue May 31, 2022 2:43 pm

Dave Moll wrote:...so I no longer have the means to play my large collection of material on VHS cassettes either.

Similar situation with many now defunkt formats. Think of floppies, particularly the 5.25" and 8" varieties, how many have the means of retrieving any data on them? I have no means of reading 3.5" versions and haven't for some years now. Likewise CDs and DVDs.

I've seen this called 'digital amnesia'. Books or potentially any written format last for perhaps thousands of years, whereas newer means of storing information hardly last a generation.

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Re: Jenkins Instructions to make a radiovisor

Postby Dave Moll » Tue May 31, 2022 5:58 pm

Steve Anderson wrote:Think of floppies, particularly the 5.25" and 8" varieties, how many have the means of retrieving any data on them? I have no means of reading 3.5" versions and haven't for some years now. Likewise CDs and DVDs.


At the risk of drifting this thread even further off-topic...

I am probably in the minority now in still having access to CDs, DVDs and 3½" floppies, along with the facilities for extracting information from 5¼" floppies. Although I have both 8" floppies and drives, the drives are not currently in a usable state.
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Re: Jenkins Instructions to make a radiovisor

Postby Steve Anderson » Tue May 31, 2022 7:58 pm

Dave Moll wrote:...Although I have both 8" floppies and drives, the drives are not currently in a usable state.


Therein lies one of the problems with 'digital amnesia', you may have the media, but can you read it? Unlike a book, all you need is a pair of functional eyes (thankfully most of us have at least one), an understanding of the language (also applies to any other stored data), and a source of light - the sun will do...at least for about half the day (Ignoring artificial light).

However, as usual I've taken this well and truly off-topic...let's see if we can return to where Harry meant this to go...

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