[GreenKeys] news wire photos

Fri Jun 17 15:00:32 EDT 2011

For those interested in seeing this more or less "in action" (I say "in
action" because it is in a movie) watch near the end of "Call Northside 777"
with James Stewart.  The "fax-ing" of a photo is key to proving the
convicted killer is innocent.  You can also see the receiving machine in the
movie trailer on IMDB.com at the 42 second mark.  Here is a link to the IMBD
page:

http://www.imdb.com/title/tt0040202/

By the way, I do not own teletype equipment myself, but I really enjoy
reading eveyone's posts on GreenKeys.  Even as technology moves on it is
always good to keep in touch with the foundations it came from.  Besides,
with the resurgence of vinyl LPs, we may actually get to the point where we
can send telegrams again!  (he wishes wistfully).

Enjoy!
Leonard Kyllonen

On Fri, Jun 17, 2011 at 1:31 PM, David I. Emery <die at dieconsulting.com>wrote:

> On Fri, Jun 17, 2011 at 12:46:56PM -0400, Nick England wrote:
> > I think the spark-paper method could only be used for black/white
> > imagery rather than news-quality photos - the resolution wasn't good
> > enough to provide half-tone images as used to print gray-scale photos
> > in magazines, etc. For actual gray-scale photos, the receiving paper
> > was regular light-sensitive photographic paper and a variable
> > intensity lamp was focused to create the spot on the paper. Lamp
> > intensity was determined by the incoming AFSK frequency (1500-2300
> > cps)
> > After reception, the paper was developed using normal photo chemicals
> > in a darkroom.
>
>        Transmission over HF radio was FM (FSK), transmission over
> leased wire lines was usually DSB AM with a carrier tone of 2400 Hz
> being common or sometimes 1800 Hz.   More tone, brighter light usually I
> think.
>
>        Early drum and lamp fax machines could use either sheet film or
> photographic paper depending on the need...  I believe film was quite
> common for newspaper use...
>
>        Some late era photo fax and wirephoto machines used dry silver
> paper developed by heat and fed from a roll rather than wrapped around a
> drum.   Spinning mirrors provided a scan.    And for lower quality
> images there were always the helix-on-drum moist paper electrolytic
> machines widely used for weather maps
>
>        Early machines were manually operated with a speaker to monitor
> the line inside the darkroom allowing the operator to load the film or
> paper and start the drum spinning and activate the magnet driven clutch
> mechanism that would allow the receiving machine to acquire phase
> synchronism with the sending machine as the sending operator set up to
> start transmission.
>
>        Later machines (especially the roll paper kind) used audio
> signaling tones to control start and stop of reception and initiate
> phasing.
>
>        From the early days machines generally had internal frequency
> standards (tuning fork or later crystal) to generate a highly stable and
> accurate motor drive voltage for a synchronous motor that drove the drum.
> This was required so the receiving and transmitting drums stayed more or
> less exactly in sync during the transmission of the image - if they did
> not the image would come out slanted.   60 Hz line power is no where
> near stable enough or accurate enough for this.
>
>        Many of the really early machines used a phonic wheel type
> synchronous motor to drive the drum that ran off mid audio frequency AC
> and made quite a bit of noise... later machines were more likely to just
> synthesize an accurate 60 Hz and use that through a power amp to drive
> the motor.
>
>        Most machines for wirephotos used a drum speed of either 60 RPM
> (early days) or 120 RPM (later on) though there were some 90 RPM systems
> apparently and later weather satellite APT was 240 RPM.
>
>        DSB AM audio tone wirephoto networks were around into the early
> 80s at least - used with automated printers, I do not know if there ever
> was a digital version developed for wirephotos as there certainly was
> for documents and weather maps.    More recently wirephotos are sent
> over TCP/IP on Internet or private connections as .jpegs or similar just
> as all kinds of other images are.
>
>
> --
>  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass
> 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole -
> in
> celebration of what could have been, but wasn't and is not to be now
> either."
>
> ______________________________________________________________
> GreenKeys mailing list
> Home: http://mailman.qth.net/mailman/listinfo/greenkeys
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:GreenKeys at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>