[NA-User] Two-Radio Setup for SSB?

N2GA@aol.com N2GA@aol.com
Mon, 1 Apr 2002 12:29:24 EST

Hi Dave,

    I have the same problem with my "DX Doubler".  It works great for
CW but SSB is a problem.  If you can write and distribute that DOS
program, it would be a great help.  Other than that, NA works great
for SO2R contesting.

Thanks and 73, George
George Tranos N2GA
(trustee of LIMARC Club callsign WV2LI)

My TopTen "DX Doubler" box does the same thing.  I had not dug into the 
problem but what you describe is the culprit I suspected.

If you look at the DX Doubler schematic you'll find that the TopTen boys 
made a mistake in the design of an otherwise most excellent unit.  When 
K1EA originally designed the CW keying standard for logging programs, the 
emitter of the NPN keying transistor was connected to pin 1 of the LPT 
port.  This pin is normally high at bootup, and has to be asserted low by 
the logging program.  In this way, the state of pin 17 can't cause the 
radio to be keyed until the program wants it to.  This is important because 
it appears that the initial state of pin 17 is random between different 

When N6TR added PTT control to TRLog, he simply duplicated K1EA's keying 
circuit for the PTT output, except connected to pin 16.  The same 
considerations apply - the initial state of pin 16 at startup appears 
random so the emitter of the NPN PTT transistor is tied to pin 1.

The problem with the TopTen DX Doubler is that the emitters of these 
transistors are not tied to pin 1, but are tied to ground.  Therefore, when 
you start the computer you might get unintended PTT and/or CW keying until 
the logging program is started.

There are two ways to fix this:

1. Modify the hardware.  I've not taken my DX Doubler apart to see how hard 
this would be.  Unless the PCB pattern is really dense, it should not be 
hard to isolate the emitters of the keying and PTT  transistors and tie 
them to pin 1.

2. I can make a little utility program which can be called early in the 
AUTOEXEC.BAT file to assert the LPT bits into states which are *off*.  This 
is probably the easiest route for running DOS, but I don't know how it 
would turn out under Windows.