[GreenKeys] Early Fax Machine/ NBC Radio News on the Hour

[David I. Emery]

On Thu, Dec 29, 2016 at 11:58:17PM -0500, Bruce Gentry wrote:
> Into the early 1960s the tone of a fax machine with a tympani roll in 
> the background was used as the intro to the hourly news report on NBC 
> radio. As best I can recall, the tone was amplitude modulated. However, 
> I have seen  another wirephoto machine that used FM audio tone.  

	There were two technologies used in those days... 

	The earliest was a AM modulated 1800 or 1500 Hz tone... which
continued to be widely used on voice grade wireline circuits for
newspaper wirephotos and weather fax charts and the like until digital
transmission and compression took over in the late 60s and early 70s.

	And for HF radio with selective fading and unstable levels FM'd
audio tones with around 1 KHz deviation were universally used -
sometimes on SSB voice channels and often by FM rather than FSK
modulating a HF CW transmitter with a class C final...

	The AM audio fax signal could be directly applied to a lamp of
of some kind or to spark or electrolytic styluses - the FM kind  required
demodulating the FM signal to video and either remodulating that as an
AM tone or or applying it directly to the writing path.

> Probably from the 50s or 60s, it was all tube and used a tuning fork 
> oscillator to drive the drum motor.

	That was very common, 60 Hz power was not accurate enough across
grids to keep drums in phase over the many scans of an image... so
something more accurate was needed.   Thus the tuning fork.


-- 
  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."