Mechanical Television primer

[w.mayer]

I love to do a separate room with some antic stuff inside like the a good CRT Projector an old early Tube TV and if possible some of the stuff you talk about.

I think about it since many years.
But the room I had plan for this is blocked by my daughter for the next years

[donaldk]

That trans Atlantic transmission was actually captured on a record, yup phonogram/-graph became a videograph. Low information content made that it could be captured onto a shellac disc. A number of years ago this disc was decoded using modern computer technology.

http://www.telegraph.co.uk/culture/tvandradio/11898165/John-Logie-Baird-recording-saved-by-anonymous-donor.html
http://www.tvdawn.com/earliest-tv/phonovision-experiments-1927-28/the-recovered-images/

[donaldk]

Wolfgang, so you already collected a Saba Schauinsland, and a Volksbox?

[w.mayer]

No I not have it but I may will buy some if I can get a good deal.

[albert]

Wolfgang- it would be great to have a little museum next to your projection room- but I guess your daughter would not like it!
Donaldk- I'm glad you mentioned the Baird "Phonovision" system, it was the first video recording process, long before AMPEX & co. in the 1950s. A British engineer managed to retrieve the images on these first discs - something Baird himself had never been able to do.
Today, the shellac disc of old has been replaced by the compact disc, and the low band video signals of the Baird process can be recorded on a CD-ROM as an uncompressed wave file. The sound for the video can be recorded on the other audio channel.

Mechanical television is by no means dead today. We will get to it!

The years from 1925 to 1939 were a time of feverish development. What had begun with a 30 line system and wooden discs ended here in Germany (just before the World War interrupted everything) with a fully electronic 441 line system including interlace.
The 2 MHz bandwidth of 441 line tv could not be transmitted on shortwave anymore, so TV helped bring in a new era of what we call FM ukw radio today.
But the Nipkow disc was used way into the fully electronic era, mainly for film scanning purposes. Here the inherent light loss of the Nipkow system could be compensated by using arc lights for the scanning process.
This led to one of the craziest inventions: "Zwischenfilmverfahren" in German.
If you wanted to "televise" an outdoor daylight scene, the Nipkow disc was not useable because of its light loss. So the rather incredible idea was

To film a scene on 35 mm movie film,
run this out of the camera into a super fast developing machine ...
then scan the still wet film with a Nipkow disc scanner.

This whole contraption was built into a big truck with a platform on top where the film camera stood on a hollow pedestal. The exposed film would run thru the pedestal into the truck to be developed and scanned ...and bingo! Here was your "Zwischenfilm " - in-between-film- process.
Below is a design for a 441 line Nipkow disk with several spirals and synchronization holes.
The second image shows the last Fernseh AG scanner built before the war - combined film scanner and a system like a videophone for transmitting images of the "talking head" type- 441 lines with a rotating disc in a vacuum housing. 10.000 rpms! If something goes wrong with such a monster, it's "duck and cover!"

[donaldk]

Indeed (again) Mark Schubin has presentation(s) that include descriptions of this system used at the 1936 Olympics.



Another little history in English on Fersehen AG http://people.ischool.berkeley.edu/~buckland/television.html

John Logie Baird began developing the process in 1932, borrowing the idea of Georg Oskar Schubert from his licensees in Germany, where it was demonstrated by Fernseh AG in 1932 and used for broadcasting in 1934.[2] The BBC used Baird's version of the process during the first three months of its then-"high-definition" television service from November 1936 through January 1937,[3] and German television used it during broadcasts of the 1936 Summer Olympics.[4] In both cases, intermediate film cameras alternated with newly introduced direct television cameras.<\q>
https://ipfs.io/ipfs/QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco/wiki/Intermediate_film_system.html (oops originally from wikipedia)

Fernsehkanone for the intermediate film system:



And for the Telefunke Electronic system (cameraman is Walter Bruch inventor of the PAL-system):



BTW, this site shows that Fersehen AG has also released at least two CRT TVs.
http://www.tvhistory.tv/1935-1941.htm

A glimpse is available of both the (front) lens to the and an 30 centimeter CRT set by FernSehen AG.

https://www.youtube.com/watch?v=myzbymf9C2Y

I did not know there were mechnical Television broadcasts here in Holland as well in pre-war. I just knew about the electronic TV experiments, like radio the decade before backed by Philips. http://www.tvhistory.tv/1935-TV-Netherlands.htm

[donaldk]

Phonovision:

https://www.youtube.com/watch?v=Rg6Qtdz6cwQ

[albert]

donaldk, you're faster than a speeding bullet! Thanks for showing these pictures- I was kinda baffled as to how to translate the German "tapeworm" of a word "Zwischenfilmverfahren". Intermediate film...easy.
https://www.youtube.com/watch?v=Gla8EYivPVA

This documentary shows some of the retrieved footage done with the intermediate film process. Thanks to these images- from about 11 minutes into the film- we can imagine today what the "programs" must have looked like. The documentary can be found under several names - the link I posted had the best image quality but it is in German. If you want to find the English versions google for "Television Under the Swastika".
BTW- the images above show the "TV Cannon " iconoscope camera used during the '36 Olympic Games - the intermediate film camera was much smaller and mounted on a truck - it, too, can be seen in the documentary film.
Fernseh AG became one of the "motors" of television technology- one of it's founding fathers was none other than John Logie Baird. He was disappointed with the BBC and so turned elsewhere to find business partners.
In Pre war times, Fernseh AG was in touch with the American tv developers at RCA . The US lab had trouble finding suitable phosphors for their CRT tube development. The German side  gave them this stuff and in turn received an Iconoscope from Dr. Zworykin. This was quickly duplicated and found its way into the Fernseh-Cannon camera. The other system, Farnsworths Image Dissector tube was also duplicated in Germany. But I digress...we are still "mechanical" at the moment......

[donaldk]

Actually the biggest of the two TV Cannons was the intermediate film one, that one like the electronic iconoscope one it came in a long distance version. At least the sources for those images declare that the long one with the large white box at the end is for the intermediate film process. Those cannons use huge lenses. I showed the intermediate film processing version first, followed by the iconoscope one manned by the PAL inventor. You are refering to the one directly on top of the truck, more or less a regular 35mm (or split 35mm =17.5mm) film camera (Zeiss Ikon?), that was used for capturing from coser distances (wider shots with the long lens ones for close ups, I gather).

Speaking of RCA and CRT (kinescope): https://www.youtube.com/watch?v=a7U_VLzPN8w Promotional film for the introduction at the 1939 New York World Fair.

[albert]

Sorry, donaldk, both of the images you posted show the iconoscope camera. The intermediate camera was much smaller and it came on top of a truck, much like in your drawing. To my knowledge the stationary camera in the stadium did not use the intermediate process. They also had smaller tv cams with the Farnsworth dissector tube - referred to as "Sondenröhre" in the old FERNSEH  AG litterature.
The very large lens diameter of the Olympic Cannon clearly indicates  the iconoscope camera. The target of  the iconoscope was much larger than a 35 mm frame. This accounts for the lens diameter, which would not make sense for an outdoor daylight film camera. The extremely long focal length was needed in the stadium.
I have attached  an image of the "Zwischenfilm" truck.

I refer you to these pages:
http://www.fernsehmuseum.info/walter-bruch.html
Gert Redlich's virtual tv museum is a great source of information. It takes a long time to read thru all of this, though. And its in German...

I'd just love to know how to get images directly into the text .....so far I have not been able to find the trick.

[donaldk]

If they are hosted somewhere online (the dci-forum mediagaller no longer works for me, you might try that to upload images). Type
[code]

Or linking a version hosted elsewhere, I found through google:

[albert]

Thank you, I'll try this!

Today I would like to look at early methods of synchronizing the Nipkow disc to the video signal. This was a difficult problem-perhaps THE problem-of early television.
Bairds first experiments simply had the transmitter and receiver discs running on the same shaft....until he had worked out the problems of capturing and amplifying the video signals.
But as soon as transmitter and receiver were in separate rooms, there had to be another way...
And when the first TV broadcasts started, the Nipkow receiver had to comprise a means of synchronization.
The easiest way would have been to use the 50 or 60 hz line frequency for this. But in the beginning of the "electric" era, the line frequency could differ during the day or even in different parts of the city or country. So that did not work in the early days.

The solution most often used was the "phonic wheel". Invented by LaCour in 1875, the phonic wheel was the first synchronous motor. Baird used a variation of this on his "televisor".
In its simplest form, the phonic wheel had a toothed gear on the motor shaft with the same number of teeth as there were lines in the video image. Two electromagnetic coils were set 180 degrees off this wheel with their pointed iron cores as close as possible to the teeth of the wheel.
The video signal was amplified, inverted (?) and run directly into the phonic wheel assembly on the motor shaft driving the disc. For this to work, it was necessary to regulate the "wild" motor speed as closely as possible to the desired speed of 750 rpm.
The video signal à la Baird contains a sync pulse indicating a new line and another one indicating a new frame every 30 lines.
This was simply a black "bar" around the image. 
When the motor ran too fast the impulses in the coil would "brake" the gear a little , pulling on the back side of the teeth.
When the motor was too slow the coils would give a small acceleration to the gear teeth, pulling on the advancing side of the wheel's teeth.
This worked in theory and the image would stop rolling vertically. ....but only if there was no black signal between different scenes and no scenes that were too dark. If this happened the sync would be lost.
The primitive system would take care of the general speed of the disc but not of the "line sync" or phase . If this was wrong you would see a picture split in half vertically.
To correct for this phase error, the entire assembly of the coils on the motor could be rotated  slightly with a knob on a gear.

Here are the original patent drawings and a page from an original Baird manual showing the motor and synchronizer. Note that the gear wheel on the motor shaft was made from many thin metal leaves like a modern transformer core.

"Watching TV" at the time was work and no job for "couch potatoes! "

[donaldk]

Issue with attaching and embedding images is that we get to see them twice.

Here are the original patent drawings and a page from an original Baird manual showing the motor and synchronizer. Note that the gear wheel on the motor shaft was made from many thin metal leaves like a modern transformer core.



"Watching TV" at the time was work and no job for "couch potatoes! "

[albert]

Since the Nipkow disc had many disadvantages, people looked for alternatives early on. To use the mechanical process for projection of the image onto a screen, the mirror drum invented by Lazare Weiller was used and improved for tv purposes by German professor Karolus in the 1930s.

This was a heavy piece of engineering and it required lengthy adjustment since the mirrors had to be perfectly aligned. Due to the weight mirror drums were difficult to synchronize.
Another idea was the mirror screw, the images could be viewed directly and they were a lot brighter than anything on the Nipkow disc. But again, a great deal of precision was necessary.

[albert]

A very nice pocket sized televisor was made in France in the 1930s, the Brami Visiola.  It used a 30 Line  mirror screw. To view either German/French TV or UK/Baird type tv, the whole device could be rotated to run either in a vertical or horizontal position.
As all mirror screw devices, this one had to be lit by a very long, small neon lamp that was longer than the screw itself.
This  was the "smartphone" size display of its day.