[Trlog] 2 radios one com port

[Mark Shaum]

Dale asks:

- Does this mean TRLog WILL work with two radios on one serial port? -

Tree already replied on this one, but I thought I'd bring up a long-ago
project.  Way back when, I had to share an external RS-232 modem between
two terminal devices, with one serving as a RS-232 "sniffer".  Isolation
diodes were used on the terminal port transmit data lines.  Data
received from the modem was sent to the rx in data lines on both
terminals.  Either terminal could talk to the modem as long as both
didn't transmit at the same time. The diodes prevented the tx outputs
from the terminals from shorting each other out.

A single serial port could in similar fashion be hooked to two radios.
Both radios would receive the RS-232 data from the serial port at the
same time, and presumably with radio addresses in place, the radio that
wasn't being addressed would ignore anything not sent expressly for it.

A problem would arise if both radios tried to talk back to the PC at the
same time.  The result would be a collision and garbled data.  If the
software could re-poll and hopefully only the targeted radio would then
reply.  With some sort of ack/nak or packet header protocol in place, it
might work, but I suspect recovery from collisions would just take too
long at RS-232 speeds.  A message-buffered interface and hardware
handshaking might help, but this goes well past the cost and complexity
of a Y-cable and a few diodes.

73! - Mark K9TR
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Mark Shaum K9TR
email: k9tr at dtnspeed.net
http://www.qsl.net/k9tr
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