[RTTY] Multi Computer SO2R with N1MM

[Mark n2qt]

In W0YK's email on AA5AU's WPX notes in talking about using N1MM
for multicomputer SO2R he stated:

"I found that the interlock is very slow and 2-3 characters overlap
transmission from both radios.  OTOH, no software interlocks can guarantee
the absence of two signals, if even for milli-seconds, so the operator is
responsible via a hardware interlock to not transmit simultaneously."


Since I had used this approach to operate SO#R I decided to measure
any possible overlap.  I would set one rig to cq and then interrupt it by
transmitting on the other rig.  I did this where one rig was controlled by
a networked computer and then with the more typical single computer
N1MM SO2R.  I used a storage scope to look at the rf output from the
rigs.

For the networked computer configuration the the worst case was 566ms
of overlap with typical overlaps of over 400 ms.   As Ed stated this is long
enough for several characters to be sent in violation of one signal at a 
time.
Some other interlock is needed for rule compliance.

However when using N1MM in its more typical single computer SO2R mode,
it is obvious the programmers worked to eliminate this overlap.  There 
typically
was a 20 - 40 ms gap with NO RF emitted, between one rig's transmit signal
dropping and the second rig's transmit coming up.  After many sequences I 
did
manage to get one series where there was just about 44ms of overlap.  This
is well less than one half character's worth of time.  I personally feel 
good about
this performance.

The computer used was a HEX Core AMD running WinXp.  I had multiple receive
windows, packet,  along with two instances of CWSkimmer running.  I assume
for the rare instance of overlap, it was induced by a poorly timed resource 
demand
from one of these other applications.   N1MM was set for last one wins for 
SO2R
priority and 'stop other rig's transmit when this rig transmits' networked 
priority.

Mark n2qt