[CQ-Contest] Serial ports and packet

Kenneth Earl Harker kharker at cs.utexas.edu
Thu Feb 5 23:59:04 EST 1998

     I imagine someone else here must have thought about this before...

     At the U.T. club station, we have two tables full of radio gear - one
with the HF station and the other with the VHF/UHF weak signal station.  At 
the moment, our only contest logging PC we have is sitting at the HF table,
but I would like to get another PC for the VHF table as well.  Now, we only
have one TNC/radio combination for packet clustering.  I would like to be able 
to use the packet gear on either machine.  I know we could fire up a copy of 
TR on each machine, run a two computer network, and be able to get to the 
packet that way...  But, that's kind of cumbersome, especially since (possibly
with the exception of Field Day) we're very unlikely to be actually using both 
machines for logging in the same contest.  

     So, one way to do this is to put in a manual switch box on the serial line
so only one computer is connected to the TNC at a time.  But, my ideal 
situation is that if and when either or both machines are on, they can get to 
the TNC; the keystrokes of one machine get echoed on both machines, and the 
incoming traffic appears on both machines as well.  And of course, if only one 
machine is on, it works just like you would expect.  This would be both
interesting for the off-time contest operators and visitors to check out the 
cluster traffic and maybe work on strategy, and it would make for one less 
switch box to deal with in casual day-to-day DXing and grid-chasing.

    So, the question is, can one create a serial Y-cable that supports this?
If you just Y off each of the 25 lines will it likely work?  Do you need
diodes in certain of the lines to make sure things go the right direction?
Would it matter if one leg of the Y is longer than the other?  Or is it just 

Kenneth E. Harker      "Vox Clamantis in Deserto"      kharker at cs.utexas.edu
University of Texas at Austin                  Amateur Radio Callsign: KM5FA
Department of the Computer Sciences         President, UT Amateur Radio Club
Taylor Hall TAY 2.124               Maintainer of the Linux Laptop Home Page
Austin, TX 78712-1188 USA            http://www.cs.utexas.edu/users/kharker/

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