[GreenKeys] Audio to TTY Was: iPad in the Pelican Case...

[Ralph Mowery]

----- Original Message ----- 
From: "Cory Heisterkamp" <coryheisterkamp at gmail.com>
To: <greenkeys at mailman.qth.net>
Sent: Friday, September 07, 2012 11:04 AM
Subject: [GreenKeys] Audio to TTY Was: iPad in the Pelican Case...


> Dan, that sounds like something I'd like to try. Pardon the silly
> question from the uninitiated, but what sort of hardware would one
> need to convert the audio into TTY code? I'm assuming output is
> current loop. Are there models to look for? To avoid?
>
> Thanks,
> Cory
>
>

If the tones are good such as from the telephone lines or internet, just 
about anything will work that converts the two tones to a current loop.  If 
comming in from a radio receiver, it often takes a beter unit.

Look on E-bay under RTTY.  They have several on sell now.  Here is one 
example of one.
320977987987  is the ebay item number.  This unit should work reasonable 
well for signals comming off a radio receiver.   Hook up is simple.  Audio 
from the speaker hooks up to the audio input and you have two wires comming 
out for the current loop.


The signals are two audio tones sent one at a time.  Often 2125 and 2295 hz 
for hams.  The audio is fed into a converter such that when the 2125 tone is 
being received, a 60 milliamp current is generated and when the 2295 tone is 
received, the current loop is broken.   The tones switch several times at 
around 22 miliseconds each and at the end of that, the printer will strike a 
leter on the paper.