Serial Port on K3

[N4CW]

Saturday, I was preparing my mobile station for the NCQP on Sunday. I was  
using external power
to my K3 from a fully charged AGM battery. Running 50 watts into a good  
antenna, everything seemed
okay; I made a lengthy 40M CW contact and next hooked up my laptop for  
logging. That's where I ran
into trouble. I use N1MM Logger (ver 12.2.2), the serial port for rig  
control, and the parallel port for
keying. However, I couldn't get the frequency to display, yet I could key  
the rig using N1MM. To make
a long story short, I found that (using the K3's metering), my supply  
voltage was 12.3 volts. I substituted an AC supply (receive mode only because my
 inverter/converter was only rated for 75 watts!!!) that puts out 13.8 VDC,
and  VOILA! I got my frequency displayed.
 
I didn't have time to figure out a solution, so I wound up operating  
without rig control...single band, "rover"
class, CW only, and would type in my run frequency to set the logger.
 
So, is the K3 serial port supposed to crap out when the rig's voltage  
supply isn't optimum?
 
Bert, N4CW
 
 
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[Jim Rhodes-2]

Actually you don't know if the problem is with the rig or the serial port
on the computer. One or the other is out of spec as IIRC an rs232 port
should respond at +/- 9 volts. If you have a scope handy you might sniff
out the signal voltages on the data lines and see what the swing is.

Jim K0XU Sent from my Xoom tablet
On Feb 27, 2012 11:04 PM, <[hidden email]> wrote:

> Saturday, I was preparing my mobile station for the NCQP on Sunday. I was
> using external power
> to my K3 from a fully charged AGM battery. Running 50 watts into a good
> antenna, everything seemed
> okay; I made a lengthy 40M CW contact and next hooked up my laptop for
> logging. That's where I ran
> into trouble. I use N1MM Logger (ver 12.2.2), the serial port for rig
> control, and the parallel port for
> keying. However, I couldn't get the frequency to display, yet I could key
> the rig using N1MM. To make
> a long story short, I found that (using the K3's metering), my supply
> voltage was 12.3 volts. I substituted an AC supply (receive mode only
> because my
>  inverter/converter was only rated for 75 watts!!!) that puts out 13.8 VDC,
> and  VOILA! I got my frequency displayed.
>
> I didn't have time to figure out a solution, so I wound up operating
> without rig control...single band, "rover"
> class, CW only, and would type in my run frequency to set the logger.
>
> So, is the K3 serial port supposed to crap out when the rig's voltage
> supply isn't optimum?
>
> Bert, N4CW
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
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[Jim Brown-10]

On 2/27/2012 8:48 PM, [hidden email] wrote:
> So, is the K3 serial port supposed to crap out when the rig's voltage
> supply isn't optimum?
>  

Several questions.  First, how are you powering the rig?  Two wires
straight to the battery?  What conductor size?  How long? Did you have
two wires running to the battery, or were you using chassis as return?  
The latter is a recipe for disaster.

  How were you powering the computer?

What was the "good antenna?"  Was it a mobile antenna or an antenna
rigged separately from the vehicle, like a dipole strung in trees?  
Thanks to paint between sections of the body, the chassis bonding in
many cars ranges from awful to non-existent, and antennas attached to a
car use the chassis as return for antenna current.  This current can
wreak havoc with any electronics in the vehicle.  Even a ground-mounted
vertical close to the vehicle can do that too.

What was the serial cable? Was it twisted pair or parallel wires inside
a shield? Parallel wires inside a shield are very subject to the strong
magnetic fields produced by antenna current.  Twisted pair provides FAR
better immunity from RFI.  See

http://audiosystemsgroup.com/RFI-Ham.pdf

for details of how to build a serial cable with far better RF immunity,
and other advice on avoiding RFI problems in a mobile installation.
There's also detail about that cable in
http://audiosystemsgroup.com/HamInterfacing.pdf

73, Jim Brown K9YC


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