[GreenKeys] Air Force TT-21/FG - Not "normal" - oops - wrong link

[Nick England]

The TT-21 is a Receiving Transmitter Distributor used to read the one-time
key tape in a crypto system known as PYTHON or SIGTOT.

An external "mixer" unit combines the key tape with the text tape (or
keyboard or RTTY). At the sending end, the key tape gets mixed with plain
text to produce encrypted text. At the receiving end, the encrypted text
gets mixed with an identical key tape to produce the original plain text.
The "mixing" is binary addition aka exclusive-or.

The "receiving" function of the TT-21 uses the short rotor segments to
sample the incoming text in the middle of each bit (you can also see a
rangefinder lever). Each sampled bit signal is connected to the
corresponding tape hole signal such that the mixer can do the right thing:
mark+mark=space, mark+space=mark, etc.

The TT-21 shaft runs slightly faster than 60 wpm so that the key tape can
always keep up with the incoming text characters.

The Navy called the TT-21 a CSP-2699. You can find the TT-21 tech manual TM
11-2222 and more info on my crypto page at
http://www.navy-radio.com/crypto.htm

The ebay seller also has a TT-21A but it looks like the special rotor has
been replaced with a regular one.

Cheers
Nick

On Monday, October 10, 2016, David Burns <dvdbrns at rcn.com> wrote:

> Nuts...the original link is a normal TD, this is the odd one.
> <http://www.ebay.com/itm/US-Military-Radio-Repair-Teletype-Tape-Machine-Model-15-19-11-16-tt-21-fg-/172369355224?hash=item282203a1d8:g:xZwAAOSw8gVX-nqS>
>


-- 
Nick England K4NYW
www.navy-radio.com
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