[GreenKeys] Tone frequency history?

[Nick England]

I wonder why 425 Hz tuning forks would have been common? Musical A is 440
and A-flat is 415.3.
Maybe 2125/2975 came first and then 425 tuning forks? Hmmmmmmmmm.
Nick

On Fri, Oct 8, 2021 at 9:46 AM Ralph Mowery <rmowery42 at charter.net> wrote:

> For the space high/low the reason is that at first rtty was mostly sent by
> putting a capacitor across the tuned circuit of the transmitter oscillator.
> This caused the frequency to shift down for the space. As people started
> using rtty on frequencies about 30 MHz they could use audio in the AM or FM
> modes instead of just shifting the carrier.  So the demodulators were built
> using the space as the high tone.  As ssb came about it was discovered if
> you feed a single tone into the microphone of a SSb transmitter your signal
> would be a single frequency if the tone was a pure sine wave.  This lead to
> the use of lsb on all bands for rtty as the frequency shift would be
> inverted .  That is if audio shift is up 170 or 850 hz and you use lsb the
> RF output will be that much lower.  If usb is used then the RF output would
> be higher.  The ham on the receiving end could set his receiver to the
> sideband that matched his filters which was most often lsb.  Rtty really
> confuses many in that you can set your receiver to either usb or lsb and
> then switch the demodulator to 'normal' or 'reverse' and with the correct
> combination you will receive the rtty correctly no matter what the
> transmitter is doing.
>
> Not sure if true or not,but the reasons for 2125 and 2295 is music tuning
> forks of 425 hz were easy to find years ago.  The 2125 is the 5 th harmonic
> and 2295 is the 7 th harmonic.  By using an oscilloscope it was easy to
> look
> at the pattern and see if your frequency was correct.  Remember this is way
> before hams had frequency counters and the receivers were as stable as they
> are now.That is the reason for the 850 hz shift and the FCC had a rule the
> shift could not be over 900 hz.  As things improved over the years the 850
> hz shift was divided by 5 to get 170 hz shift.
>
> Ralph ku4pt
>
>
> -----Original Message-----
> From: greenkeys-bounces at mailman.qth.net
> [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Harold Hallikainen
> Sent: Thursday, October 07, 2021 10:31 PM
> To: greenkeys at mailman.qth.net
> Subject: [GreenKeys] Tone frequency history?
>
> 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
>
>
> ______________________________________________________________
> 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 navy.radio at gmail.com
>
-- 
Nick England K4NYW
www.navy-radio.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20211008/c23d2f60/attachment.html>