[GreenKeys] TTY loop interface

[John, W9DDD]

That would be the tempest version, right?



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The above comments or recommendations are SWAG. Use at your own risk.
John, W9DDD

On 8/12/2021 8:44 AM, Nick England wrote:
> FWIW Here’s the M28 SMD that runs off 48v
> https://www.navy-radio.com/manuals/tty/wd/323810WD-SMD.pdf
> 
> 
> 
> On Thu, Aug 12, 2021 at 8:55 AM Jim Haynes <jhhaynes at earthlink.net 
> <mailto:jhhaynes at earthlink.net>> wrote:
> 
>     On Thu, 12 Aug 2021, Nick England wrote:
> 
>      > Well perhaps Jim is the father of low level +/-6v signaling that was
>      > implemented for TEMPEST purposes. The TH-83 hubbing repeater is
>     exactly what
>      > he describes. See
> 
>     At the time I was working on the low-voltage selector magnet driver,
>     when
>     I had been asked to work on a solid state replacement for a polar relay.
>     And I felt that these were two separate problems - if we need an
>     interface
>     to a 60ma loop coming in from the outside world, and we need a way to
>     drive selector magnets with solid-state circuits.  TEMPEST didn't
>     come up
>     as an issue in that little project.  But I did realize that the low
>     voltage hub scheme would be a way to interconnect a station as well as
>     a way to organize the interior of a set.  The military folks came up
>     with the TEMPEST problem and its various solutions, and then EIA came
>     up with the low voltage polar interface as a way to standardize the
>     connection between a customer-premises modem and the data equipment.
>     This was a bending of the old telephone company "no foreign equipment"
>     policy because AT&T realized there was a market for data transmission
>     over the switched network and that they couldn't possibly provide all
>     the kinds of equipment that customers might want to connect.  Western
>     Union also developed a line of low-voltage equipment, probably in
>     connection with DOD.
> 
>     I didn't design the low voltage selector magnet driver as it turned
>     out to be - I had envisioned simply a saturated transistor, and someone
>     else came up with the constant-current circuit that was ultimately used.
>     Maybe that was helpful in going to 110 baud.  And it was I guess someone
>     at Bell Labs who decided the interface between the original TWX modem
>     and the Teletype set should be current loop rather than voltage.
> 
> -- 
> Nick England K4NYW
> www.navy-radio.com <http://www.navy-radio.com>
> 
> 
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