[GreenKeys] Model 15 Speed Limit (Kevin DeWitt)

[Jim Haynes]

The range finder allows you to compensate somewhat for the sending
machine being faster or slower than the receiving machine.  So you can
copy 50 baud on a 45.45 baud machine, but with reduced range, and hence
with reduced tolerance to distorted signals.

The official speed limit for the Model 15 is 75 wpm.  Parts were made to
allow them to operate at 100 wpm.  Aside from the gears there are some
spring tensions that have to be changed, and other adjustments that have
to be tightened up.  This was done during WW-II where the increased
speed was considered to justify the higher maintenance requirements.

Arguably a better solution to that problem was a system that did a two-
channel time-division multiplex on the cheap.  It used a 60 wpm tape
reader where the sending distributor had the segments split in half,
each set fed from a different tape reading head.  If signals were good
enough this allowed receiving either of the two messages by setting
the range finder early or late.  The printers ran at 60 wpm.

I saw a Model 15 running at 100 wpm once, at an FAA facility where they
were trying it out.  They wisely decided to buy M28 machines instead.