[GreenKeys] Tone frequency history?

[Nick England]

AN/FGC-1 block diagram and general description is on this page
https://www.navy-radio.com/rtty-demod.htm

I think I have the manual somewhere and will scan it when I get a chance.

Nick


On Thu, Oct 7, 2021 at 11:49 PM Jerry Murphy <gfmurphy at earthlink.net> wrote:

> Hi Harold:
> The WWII era AN/FGC-1 teletypewriter terminal had mark and space filters
> in it
> that were set at 2125 and 2975 Hz.  The terminal was designed and built by
> Western Electric.  It seems likely that Bell Labs provided some design
> help.
> I don't see anything in the literature about why those frequencies were
> selected
> but there must have been a good reason.  I still have a pair of those
> filters.
>     Jerry Murphy
> -----Original Message-----
> From:
> Sent: Oct 7, 2021 8:14 PM
> To: ad7i
> Cc: greenkeys
> Subject: Re: [GreenKeys] Tone frequency history?
>
>
>
> On Thu, October 7, 2021 8:01 pm, ad7i wrote:
> > Excellent question. I've wondered about this as well.
> >
> > I don't know that this is relevant to the reason for choosing 2125 & 2975
> > Hz, but I note that
> >
> > 2125 = 17 x 5 x 5 x5
> >
> > 2975 = 17 x 5 x5 x 7
> >
> > Paul, ad7i
>
>
> Thanks! I'm seeing that before Bell 103, there was Bell 101. But I'm
> finding very little information about that. Some of the information gave
> me the idea it used amplitude shift keying instead of frequency, but I may
> have misread that.
>
> Harold
>
> --
> http://w6iwi.org
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-- 
Nick England K4NYW
www.navy-radio.com
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