[GreenKeys] [External] Photos via paper tape 1925

[Harold Hallikainen]

On Wed, April 2, 2025 8:44 am, Jones, Douglas W via GreenKeys wrote:
> From: Nick England <navy.radio at gmail.com> -- Wednesday, April 2, 2025
6:43
> AM
>> https://chicagoboyz.net/archives/73505.html#more-73505
> This is brilliant stuff.  If anyone's curious, the first Bartlane US
Patent is 1,653,425.  It gives a bit more technical detail.  I added a
citation to it to Wikipedia's article on wirephotos, which already
mentioned the Bartlane system but with references only to secondary
sources that had no good citations.
>            Doug Jones

I agree, brilliant stuff! It seems like they could have done binary
encoding mechanically. On the transmit side, the exposure time for the
film plates would increase exponentially instead of linearly (ie, 1
second, 2 seconds, 4 seconds, etc.). On the receive side, they could
similarly vary the exposure time or could have the tape reader flip
neutral density filters into the light path, again binary weighted (50%,
25%, 12.5%, etc.).

I'm guessing there was no horizontal or vertical sync. The start of the
tape was the top of the image, and each line had a know number of pixels.

When in high school, I visited a local short wave listener who printed
news photos received over the air. He would wrap photographic film around
a drum and start the machine, then develop the film. Really nice high
quality photographs resulted.

Then in the 1970s, I maintained an Alden fax machine for an FAA flight
service station. The image was delivered over a phone line as FM audio. An
insulated drum with a metal helix on it provided horizontal scanning while
the paper feed motor provided vertical scanning. The soggy paper would
turn brown where current was passed through the paper. The helix motor was
driven by a synchronous motor driven by a divided down crystal oscillator.
At the beginning of each image were several lines of black with a short
pulses of white. When this sync signals was detected, the oscillator
divider would change to slow down the motor slightly until the white pulse
lined up with a sync detector (I think it was a microswitch) on the helix
drum. Then the divider would return the motor to normal speed, and the
rest of the image would be received.

It looks like the same system is still used to transmit weather maps on
HF. For example, right now I can use a KiwiSDR to see a weather map being
transmitted on 8457.1 MHz from Kodiak AK. I am using one of the KPH
KiwiSDRs at http://198.40.45.23:8073/ . On the right, select FAX as the
extension. In the pop up on the left, select a station in one of the
regions. I tried a bunch and got a good signal at Americas - Kodiak NO3 AK
- 8459. Attached is a screenshot. Note the white rectangle between images.
On the Alden machines, this would be skewed to the left until it ended up
on the left margin. Apparently a different sync position is used now since
the white rectangle is not on the left margin, and the following image
appears to be aligned correctly.

Fun stuff!

Harold
https://w6iwi.org


-- 
Not sent from an iPhone.


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