[WriteLog] CW Sending from a Laptop

[Jim Brown]

On Mon, 28 Jun 2004 06:35:51 -0700 (PDT), Lee Buller wrote:

> The keying out of the serial port was...poor.  It sounded like the timing was off.
> It would shorten dits and dahs...or miss them all together.  I sounded like a lid.  
>I plugged a key on and sent by hand which defeats the purpose of the program. 
>Is it the program or the laptop?

I suspect the serial port or RF getting into the cable. Was it a "real" serial port, or 
was it a USB simulated serial port?  USB simulated serial ports are well known 
to have serious timing problems. 

I have very successfully used WL serial port keying with my K2/100, TS850, 
TS790, and Omni V.9, and with my IBM T22 (built-in serial port) and IBM T41 
(real serial port from a Quatech DSP100 PCMCIA card that uses a 16750 chip).  

RFI can be a problem if there is RF "in the shack." In that case, the interconnect 
cable needs to carefully avoid pin 1 problems. When there is RF in the shack, the 
shield of the interconnect cable should go to the SHELL of the DB9 connector, 
NOT to the so-called "signal ground."  Cable shields can act as receiving 
antennas, and the current they receive should flow directly to the chassis, not to 
the circuit board and then to the chassis. Why?  Simple -- there is inductance in 
the circuit trace, and the IZ drop across that inductance injects RF onto the circuit 
board!  

On my computers, the symptom of the wrong shield connection is that the 
computer will lock up into keydown. Reducing power lets keying continue. So 
does rewiring the cable to eliminate the "pin 1 problem."

I also suspect your inverter (some call it a level shifter). The NPN transistor circuit 
that is somewhere in the doc works fine for me. Wire the collector to the 
transmitter key line, emitter to transmitter chassis (key connector shell), and the 
computer DTR line drives the base through 1K ohms. My junkbox includes a 
bunch of 2N4123's, so that's what I used, but most any generic small signal NPN 
should work.  That's what we used for both radios at K9OR. One was a K2/100, 
the other a TS850. 

Jim Brown  K9YC