I have sucessfully interfaced the MFJ 432 to my lapop computers for use
with TR-Log!
There were two problems with this device and the solutions are:
1. Severe hum and feedback when powering the unit from radio power.
Solution: Jumper (short out) L6 - a ground return choke in series
with the mic and ptt ground leads. This appeared
to be an attempt to keep RF out, but what good is
it if you can't even use the unit before the TX is
enabled??
2. Only DVK channel 1 would key when interfaced directly to the computer
parallel port.
Solution: Put 1N914 diodes in series with keying lines to DVK
channels 1,2 & 4 (not channel 3) from the computer
parallel port. It is possible that the diode on
channel 4 may not be needed either, but 1 & 2 are
a must!
Reasoning: The internal inputs of these keying lines have diodes
from Channel 2 to 1, Channel 3 to 2. This causes
a path back to ground through the parallel interface
causing the fired input to be held
"low" through the internal diodes and prevent the firing
channels from reaching a high enough logic level to work.
I have this setup on two laptops and keyers. They perfomed perfectly
during the NAQP SSB contest this weekend.
--
Thomas M. Delker - K1KY CFO#395 - Smyrna / Gallatin / Short Mtn. TN
A.R.R.L. District Emergency Coordinator - Tennessee District #4
C.A.T.S. (W4CAT) - 147.30/145.23/145.49/145.17/223.98/444.45/444.65
Stones River A.R.C. (K4FUN) - http://www.members.home.com/srarc
Tennessee Contest Group (K4TCG) - http://www.k4ro.net/tcg.html
Fistfighters United Nashville (NT4L) 146.955 (114.8)
--
FAQ on WWW: http://www.contesting.com/trlogfaq.html
Submissions: trlog@contesting.com
Administrative requests: trlog-REQUEST@contesting.com
Problems: owner-trlog@contesting.com
Feature Wishlist: http://web.jzap.com/n6tr/trwish.html
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