Re: Load coils and bridge taps


<harold@xxxxxxxxxxxxxxx> wrote in message
news:20070916062309.GB7311@xxxxxxxxxxxxxxxxxxxxx
On Sep 14, 11:00 am, Neal McLain <nmcl...@xxxxxxxxxxxxxx> wrote:
There's an excellent article about load coils and bridge taps, provided
by
USMILSCOM, athttp://www.usmilcom.com/docs/Load_Coils.htm.

Neal McLain

***** Moderator's Note *****

My first introduction to loading coils was as a ham radio operator: we
used them to make the "Terminal Units" that converted radio signals
into the Baudot code used by Model 15 teletypes. The TU's were modems,
made with two audio filters, one each for mark and space signals.

This was, of course, before the computer age: making a filter for 2975
Hz required a _lot_ of inductance, and 88 mh toroids filled the bill.

Bill Horne
Temporary Moderator

I did the same thing! I made vacuum tube terminal units with 88mH
toroids. I ran 850Hz shift with frequencies of 2125 and 2975 Hz. This
drove a 60mA current loop for my model 15 Teletype, model 14 typing
reperf, and model 14 transmitter distributor. All this on 80 meters.

Harold
WA6FDN

That's pretty much my setup back in the early '60s. I still have the
terminal
unit but gave all of the TTY stuff to some sort of museum.

Try finding a H-88 load coil today that isn't encasulated.

***** Moderator's Note *****

Well, then, we were both ahead of our time ;-). As fate would have it,
my father put my model 15 out for the trash while I was in Vietnam.

Now, to keep this within the realm of teleocm, I'll add this note:
the Model 15/19, and (later) the model 33 Teletype machines were used
extensively in the TWX network, which was the Bell System's competitor
of the Western Union TELEX network.

In 1976, I went to Chicago to learn how to maintain Model 32/33
Teletypes, which had largly replaced the older equipment. Model 32 was
fitted for BAUDOT code, and the Model 33 was an ASCII machine: the
Model 32 was intended for TELEX use, and the Model 33 for TWX.

Bill Horne
Temporary Moderator


.