[GreenKeys] ITTY 850 shift?

Harold Hallikainen harold at w6iwi.org
Sat Feb 4 21:54:14 EST 2023 

When I worked in radio stations (1970s), the AP and UPI wire services had
a bunch of different TTY channels on the single telco pair. The
demodulator was tuned to whatever service you were subscribed to.

I still plan on doing some experimenting with 850 Hz vs 170 Hz shift. I'm
currently thinking that the error rate would be about the same on 170 Hz
shift with use of either a limiter or dynamic threshold control. With 850
Hz shift, I think dynamic threshold control would do better since the
wider apart frequencies would fade differently (at least more differently
than with 170 Hz shift). I think a fade of 170 Hz shift signal would
frequently take both tones below the noise level while with 850 Hz shift,
perhaps only one would go below the noise level at a time.

My DSP TU ( https://w6iwi.org/rtty/DspTU/ ) has a simple error counter.
The number of valid start bits is compared to the number of valid stop
bits (in a software UART). With a high error rate, the ratio of valid stop
bits to valid start bits will be lower.

It would be interesting to also implement this on a computer for testing
different terminal units under impaired channel conditions. I know the
FTDI USB/UART bridge won't go down to 45.55 bps. It looks like hardware
serial ports on PC compatible computers can hit 44.956 bps, so that would
be something to try. The error rate would be the number of frame errors
divided by the number of bytes received.

Anyway, I think there may be advantages to 850 Hz shift with selective
fading and dynamic threshold control.

Harold
https://w6iwi.org


On Sat, February 4, 2023 7:30 pm, W2HX wrote:
> Interesting idea. I'd be happy to test it. I can demodulate both shifts.
> Very interesting experiment!
>
>
> 73 Eugene W2HX
> Subscribe to my Youtube Channel: https://www.youtube.com/@w2hx/videos
>
>
> -----Original Message-----
> From: greenkeys-bounces at mailman.qth.net
> <greenkeys-bounces at mailman.qth.net> On Behalf Of Harold Hallikainen via
> GreenKeys
> Sent: Saturday, February 4, 2023 9:10 PM
> To: Daniel Jones <djones at k6yic.com>
> Cc: Greenkeys <greenkeys at mailman.qth.net>
> Subject: Re: [GreenKeys] ITTY 850 shift?
>
> I wonder if those tones (2 kHz +/- 425 Hz) are far enough away from the
> 170 Hz shift tones that both could be sent on the same channel and the
> terminal unit would demodulate the correct ones.
>
> Harold
> https://w6iwi.org
>
>
> On Sat, February 4, 2023 6:57 pm, Daniel Jones wrote:
>> As a fellow military user I concur.
>>
>>
>>
>> Daniel
>>
>> www.K6YIC.com
>> DJones at K6YIC.com
>>
>> HH#11973
>>
>>
>>
>> On Feb 4, 2023, at 17:54, Nick England  wrote:
>>
>>
>> Paul, definitely use these military tones and not the ham ones
>> that
>> Jim Haynes discussed. No one is running 850 shift any more except us
>> guys running military gear. Our equipment is not retunable to the ham
>> tones.
>> Thanks
>> Nick
>>
>>
>>
>>
>> On Sat, Feb 4, 2023 at 8:29 PM W2HX  wrote:
>>
>>         That would be cool! Center freq 2000 Hz, shift is +/- 425 Hz
>> so that means the tones are 1,575 Hz and 2,425 Hz. Mark is low.
>> Someone correct me if I’m wrong.
>>
>>
>>
>>
>>
>>  73 Eugene W2HX
>>  Subscribe to my Youtube Channel: https://www.youtube.com/@w2hx/videos
>>
>>
>>
>>
>>   From: Paul Heller
>>  Sent: Saturday, February 4, 2023 7:58 PM
>>  To: W2HX
>>  Cc: Daniel Jones ; Greenkeys
>>  Subject: Re: [GreenKeys] ITTY 850 shift?
>>
>>
>>
>>  Let me see what I can do. What are the frequencies for 850 shift,
>> mark and space?
>>
>>
>>
>>  Paul
>>  W2TTY
>>
>>  ITTY:                      HTTP://INTERNET-TTY.NET:8000/ITTY
>>  ITTY100:               HTTP://INTERNET-TTY.NET:8010/ITTY100
>>
>>
>>
>>  AUTOSTART: HTTP://INTERNET-TTY.NET:8030/AUTOSTART
>>  EUROPE:              HTTP://INTERNET-TTY.NET:8040/EUROPE
>>
>>
>>
>>
>>
>>
>>   On Feb 4, 2023, at 5:53 PM, W2HX  wrote:
>>
>>
>>  
>>  Thanks, Dan. I can generate the tones ok. I was just hoping that I
>> could get some news stores to print. It would be great if the ITTY
>> powers that be could just pipe the same data to both a 170 Hz shift
>> and an 850 Hz shift audio stream.  Dunno what is involved with that but
>> just curious.
>>
>>
>>
>>  73 Eugene W2HX
>>  Subscribe to my Youtube Channel: https://www.youtube.com/@w2hx/videos
>>
>>
>>
>>   From: Daniel Jones
>>  Sent: Saturday, February 4, 2023 7:46 PM
>>  To: W2HX
>>  Cc: Greenkeys
>>  Subject: Re: [GreenKeys] ITTY 850 shift?
>>
>>
>>
>>  I had a cast set up to broadcast tty over the internet.  Let me look
>> this week and see if it’s still running on my site and the feed
>> something into it at 850 shift.
>>
>>
>>
>>
>>  You can also change the settings on the itty software to the required
>> tones to test it in-house.
>>
>>
>>
>>
>>
>>  Daniel
>>
>>  www.K6YIC.com
>>
>>  DJones at K6YIC.com
>>
>>  HH#11973
>>
>>
>>
>>
>>
>>
>>
>>
>>   On Feb 4, 2023, at 16:34, W2HX  wrote:
>>
>>
>>  
>>  Anyone know if there is a URL for ITTY for 850 shift?
>>
>>
>>  73 Eugene W2HX
>>  Subscribe to my Youtube Channel: https://www.youtube.com/@w2hx/videos
>>
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>>
>>
>>
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>>
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>>
>>
>>     Jordan Spencer Cunningham's GreenKeys Search Tool:
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>>
>>  >>> 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
>>
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>> --
>>
>>
>> Nick England K4NYW
>> www.navy-radio.com
>>
>>
>>
>>
>>
>>
>>  ______________________________________________________________
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>>
>> 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
>> djones at k6yic.com
>>
>> ______________________________________________________________
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>>
>>>>> 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
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>> harold at w6iwi.org
>
>
> --
> FCC Rules Updated Daily at http://www.hallikainen.com Not sent from an
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>
>>>> 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
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