[GreenKeys] Teletype model 15 - It works!

[Harold Hallikainen]

I finally got the model 15 I picked up at last year's Hamvention running
on a local loop! I spent last weekend cleaning and lubricating it. At the
Hamvention, I also bought some 2.2k 10W resistors to set the loop current,
but lost them in the shack. Found them today!

For the loop supply, I'm using this from RTTY Electronics:

152950 150ma $20.00 - It is a small open metal chassis with a transformer,
a couple silicon diodes, and a capacitor. It has a D-hole that accepts an
HKP fuse holder. I added a fuse holder, a line cord, and a terminal block
for the DC output.

I bought some ribbons from Amazon:

Swartz Ink SI-83-BKTEL-X2, package of two (each includes two reels and
reversing rivet), $7.00 + $4.99 shipping

Since the machine did not have a keyboard, I bought one from RTTY
electronics. There was a slight disagreement between the base and the
keyboard as to wiring. Adding a jumper on the connector on the keyboard
resolved the issue.

A couple interesting things:

The typing unit seems to ignore CR but does a CR and LF on LF.

The keyboard has a bar on the right that is pulled forward by the space
bar. I THINK this lets you hold down the space bar for multiple spaces.
But my cover does not have a notch for that bar. Putting the cover on
mashes that bar down so the space bar doesn't work anymore. Right now, I'm
running without the cover. I guess I'll get out the hacksaw and cut a
notch in the cover for that bar.

Anyway, next item is a TU. I'm thinking of doing it in software on a
microcontroller. I'll do a couple biquad band pass filters for mark and
space, use the absolute value and LPFs for envelope detection, then
another slow LPF to set the threshold for the mark to space shift,
probably with some hysteresis. For transmit, I'm thinking of doing direct
digital synthesis in software. A little different from my home built TU of
55 years ago with 88 mH loading coils and a 6L6 to key the loop. For
transmit back then, I directly shifted the VFO in the Viking Ranger with a
diode switch.

Current thoughts, anyway!

Harold


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