[GreenKeys] Tone frequency history?

[Harold Hallikainen]

Once again, fascinating stuff! The constant RF advantage of FSK seems
especially true once there is an AGC in a receiver, though I guess a slow
AGC could keep the noise down during on/off keying. My transceiver
(SEA245, https://w6iwi.org/SEA245/ ) has a pretty fast AGC and no way to
turn it off. It can be annoying on CW since noise comes up between every
dit and dah.

Thanks!

Harold

On Fri, October 8, 2021 1:12 pm, Jim Haynes wrote:
> I will immediately confess that I don't know.  What became amateur
> practice no doubt came from imitating commercial practice.
>
> Going back to the 1930 edition of the AT&T Long Lines "green book"
> Principles of Electricity applied to telephone and telegraph work, there
> is a description of voice frequency telegraph carrier systems saying the
> carrier frequencies are multiples of 85 cycles (Hertz) and the channels
> are 170 cycles apart.  425 to 2295 are the channel frequencies involved.
> This system uses make-and-break keying rather than FSK.  The cover of the
> book says it is a revised edition, but I don't have the earlier one.
>
> Now we know that during and after WW-2 the standard shift was 850 Hz,
> and this was embodied in the AN/FGC-1 demodulator designed by Bell Labs.
> There is also the article by Sprague in the November 1944 issue of
> Electronics magazine which describes the FSK system used by Press Wireless
> and was the main printed source for hams in the early days of RTTY.
>
> It was fairly recently that I learned that E.H. Armstrong published an
> article in Proceedings of the I.R.E. in January 1928, "Methods of
> Reducing the Effect of Atmospheric Disturbances" in which he proposed
> using FSK for telegraphy.  This was quite some time before he got into
> the FM system for which he is famous.  His telegraph proposal did not
> use a limiter, so it was not true FM.  His hope was that the mark or
> space signal would be detected in the appropriate filter, but that noise
> bursts would affect both filters simultaneously and thus could be
> subtracted from each other.  Carson of AT&T published a comment in
> July of that year showing that Armstrong's proposal would not work.
> Although Armstrong's ink-recorder traces showed that signals received
> by FSK were clearly better than those received by make-and-break keying
> of a single frequency.  Armstrong later had some bad words for people
> who can show something mathematically when real tests with real hardware
> show a different result.  I tend to believe that the actual difference
> can be accounted for by the roughly doubling in transmitter power that
> FSK gives, since the transmitter is transmitting power all the time
> rather than only during the marking pulses.
>
> At about the same time, and presumably unknown to each other, Larry
> Schmitt of Morkrum Co. (ancestor of Teletype Corp.) filed for a patent
> 1,705,211 in 1924, issued in 1929, proposing to use FSK for telegraph
> transmission with the very same hope, that noise would cancel out as
> mark and space signals were subtracted from each other.
>
> There are various things in Bell System Technical Journal.  Such as
> "Fequency Shift Telegraphy - Radio and Wire Applications" in BSTJ April
> 1948.  Also published in AIEE Transactions 1947, p. 479.  "Carrier
> Telegraphy in the Bell System" Bell Laboratories Record, February 1948.
>
> It has long been my belief, without any evidence, that the reason for a
> shift as wide as 850 Hz was to accomodate frequency drift in the radio
> equipment.  Well one bit of evidence is that in the AN/FGC-1 the mark and
> space filters are rather flat in frequency response over a rather wide
> range, so that the signal drifting in frequency would not produce much
> change in the detector output until the drift got near the edges of
> the filters.  In the Sprague paper they used a discriminator that was
> linear over a very wide range of frequencies, and then low-frequency AC
> coupled the discriminator output to the printer driver.  So as the average
> DC level out of the discriminator varied with frequency drift the
> DC component would be removed and the difference between mark and space
> would be preserved.
>
> John Williams W2BFD of the New York area was one of the very early
> founders of amateur RTTY.  He wrote a history in QST, "The Story of
> Amateur Radio Teletype", October 1948.  Obvously at that date the story
> was only beginning.
>
> So somewhere in all that may be the explanation of how we got our
> frequencies.
>
> Jim W6JVE
>
>  	---
>
>  	"Ya can argue all ya wanna, but it's dif'rent than it was."
>  	"No it ain't! No it ain't!  But ya gotta know the territory."
>  		Meredith Willson, The Music Man
>


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