[GreenKeys] Decoding RTTY for a Teletype with a Computer / Want to Buy

[ad7i]

Chris --

If you are looking for a way to convert audio AFSK (modem) tones to
mark/space signals for a TTY, to drive a loop circuit, you might look for
something like a HAL ST-5000.  I've seen some as low as $35, but you would
need to hunt for a few months to find one at that price. The nice thing
about the ST-5000 it includes AFSK TX and RX as well as includes a loop
power source and loop keyer.  It's not a great HF radio AFSK demod, but
it's pretty good.

If you want just a way to decode ITTY modem tones (AFSK audio delivered to
you over the internet, like that from an internet radio station) you might
take a look at my JackKnife system, which is based on an Arduino
microcontroller.

      http://ad7i.net/main/projects/tty/jack-knife/

It includes a modest AFSK demodulator.  It's cheap, about $10, but you
would need to add a loop circuit and loop voltage source.  I use a
Raspberry Pi as the Internet to AFSK audio converter, and then run the AFSK
audio out of the Pi into the JackKnife to get TTY serial output at TTL
voltage levels.  The JackKnife AFSK demod is *not* suitable for HF radio
demod.  It requires a very high signal to noise ratio to work correctly,
like that found with ITTY.

73, Paul, ad7i



On Sun, Nov 1, 2020 at 10:45 AM Chris DeMuro <kn4obk at gmail.com> wrote:

> Hey everyone!
>
> I have a question, specifically about decoding RTTY on teletypes. When I
> get a Teletype, I intend to use it for several things, of which RTTY is
> just one, but I'll get to that later.
>
> As I understand it, and please bear with me as my understanding is
> limited, the RTTY audio signal is fed into some sort of decoder, and then
> the serial text output, either as ASCII or Baudot is fed into the Teletype
> to be printed.
>
> I don't have much money for this Teletype endeavor (again, I'll get to
> that) so I am trying to save a buck wherever possible. I was wondering if
> it is possible to use a computer to replace the role of the decoder, and
> send the text out of a serial port to the Teletype. I was trying to figure
> out a way to do this using FLDIGI, but I couldn't find any way of doing it.
>
> Now before you say "But that defeats the purpose of using a Teletype! Why
> even bother using a mechanical machine? Just make your RTTY QSOs on a
> computer if you feel that way!" The reason I am okay with using a computer
> as a RTTY decoder to feed text to a Teletype is the same reason I enjoy
> typing out news articles and such on a manual typewriter. I enjoy using the
> machine. I am not overly concerned with how authentic the experience is. I
> intend to use a modern radio and other such modern amenities. I think it
> would be cool to get an authentic station set up, but that is not my first
> priority.
>
> As a final note, I mainly run Linux, but if anyone has a method to do this
> with Windows software, I can make that work, so don't hesitate to let me
> know about that just because I run Linux.
>
> Now that I have rambled on long enough about that, and hopefully expressed
> my question well enough that someone can understand it, let me begin the
> next part of this message.
>
> I am looking to purchase a Teletype. I will take any model, though models
> easier to service would be preferred. I would like it to be working or only
> in need of minor repair, as I do not have much experience with this. An
> ASCII model would be ideal, but I will definitely take a Baudot machine. I
> am in Central Florida, and I have a budget of about $300. Apologies if that
> is too low. Again, I am new to all this. I have some family going up to
> Georgia later this month, so I can probably arrange to get something from
> that area as well.
>
> Please let me know if you have a machine you're looking to sell. I have
> been fascinated by these machines for a while now, and I can absolutely
> guarantee it would go to a good home, and be put into good, long-term
> service.
>
> Anyway, thanks to anyone who can get through this long email. I am too
> long-winded for my own good. :)
>
> Thanks so much to everyone who has assisted me thus far on this mailing
> list, and I look forward to hearing from you!
>
> Thank you,
>
> Chris DeMuro
> KN4OBK
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