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

Sun Nov 1 13:10:08 EST 2020

    Chris, do you have any basic texts on how teleprinters work? 
I think the members here can suggest a couple which I am sure are 
available free on the web.
    A Teletype is really a sort of mechanical computer. It takes 
a form of binary code as direct current pulses at its input and 
translates them into print characters by a purely mechanical 
means. The source of the binary signals is DC but the DC can be 
supplied by a number of devices. The most usual method for 
transmitting Teletype signals via radio is by frequency shift 
keying, one frequency for mark a second for space, but Teletype 
can also be sent by CW. FSK has some important advantages over CW 
but the results at the machine are the same. The device between 
the receiver and the Teletype converts the audio signals (they 
can also be RF signals) into the DC pulses needed by the 
machine.  A computer can decode the Teletype signal from an audio 
source and print it on the screen or send it to a computer 
printer. I think some can generate a digital signal which can be 
used by an external device to create the DC signals to drive the 
Teletype machine. It is still the Teletype that "decodes" the 
incoming signals into characters.  The whole arrangement can be 
pretty simple. A computer can make a very effective "detector" 
for incoming signals because it can discriminate between wanted 
signals and noise or interference very effectively. I think the 
loop current supply (the name of the device that drives the 
magnets in the Teletype machine) can be made fairly cheaply. 
There are also several "detectors" for converting from the audio 
frequency shift to DC pulses, which are then used for the 
machine. These also are not too expensive. There are converters 
to go from the Beaudot binary output of a Teletype to any other 
code. The range of characters on earlier machines is limited but 
later ones were used as computer terminals. If you have an 
earlier type of machine, like a Model 15, I don't know what other 
applications there are for it other than sending and receiving 
teleprinter signals. I am interested in what you are considering.
     I don't know if this is helpful, my own understanding is 
limited, but I have been fascinated by Teletype machines all my 
life and have studied about them a lot.

On 11/1/2020 7:43 AM, Chris DeMuro 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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WB6KBL