[GreenKeys] Tone frequency history?

[ad7i]

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



On Thu, Oct 7, 2021 at 10:32 PM Harold Hallikainen <harold at w6iwi.org> wrote:

> Back when I built my first vacuum tube TU with 88 mH loading coils, I knew
> that mark was 2125 Hz and space was 2975 Hz (the 850 Hz shift days). But,
> what is the history of these tones? Why were they chosen? why do we have
> space high on audio and space low on RF? I've read that tones in the 2.1
> kHz area would turn off the echo suppressors on long distance telephone
> networks. Were these tones brought over from telephone? Bell 103 does not
> use these tones. Where did they come from?
>
> Harold
> https://w6iwi.org
>
>
>
>
> --
> FCC Rules Updated Daily at http://www.hallikainen.com
> Not sent from an iPhone.
> ______________________________________________________________
> 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
>
> >>> Jordan Spencer Cunningham's GreenKeys Search Tool:
> https://teletype.net/gksearch
> >>> 2002-to-present greenkeys archive:
> http://mailman.qth.net/pipermail/greenkeys/
> >>> 1998-to-2001 greenkeys archive:
> http://mailman.qth.net/archive/greenkeys/greenkeys.html
> >>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
> http://comcents.com/tty/greenkeyssearch.html
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to ad7i at ad7i.net
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20211007/238a3bbc/attachment.html>