RE: K2 Keyer Problem

[Eberhart, Russell]

Regarding my dah-dit-dah-dit... K2 keyer problem: Thanks for the
suggestion to replace my antenna with a dummy load.  However, the
problem turned out to be related to my PSK interface.  I recently (10-15
days ago) replaced the computer I was using with my PSK interface (a
Rigblaster Nomic).  Since then, I've been running PSK and MFSK16 on 20
and 40 meters with no problem.  I hadn't gone up to frequencies above 15
MHz since installing the new computer.  It turns out that unplugging the
PSK interface from the mic input connector solves the keyer problem.
There must be some sort of ground loop associated with the "new" (less
old) computer.  The old computer was a Toshiba laptop (circa 1994)
running Windows 95.  The "new" one is a desktop (circa 1997) running
Windows 98.  I plan to dig into it a little bit more, but for now am
just unplugging the PSK interface from the mic input whenever I'm not
running PSK or MFSK16.  (For whatever it's worth, my IMD reports on PSK
are fine, so didn't suspect a problem there.)

Russ Eberhart, N9IV
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[G3VVT]

 
In a message dated 11/04/05 13:52:21 GMT Daylight Time, [hidden email]  
writes:

There  must be some sort of ground loop associated with the "new" (less
old)  computer.  The old computer was a Toshiba laptop (circa 1994)
running  Windows 95.  The "new" one is a desktop (circa 1997) running
Windows  98.


------------------------------------------
 
The addition of an extra RF filtering cap and an approx 1mH choke in  the K2
mic lead may help in removing that as an RF path into the radio.  Notes for
implementing this are on the Elecraft web site.
 
Additionally it may be worth a try adding a  600 ohm 1: 1 transformer  in the
audio path to the sound card. I found my Spectrogram test results had a  
spike at 100Hz intervals (probably 120Hz in the USA) from our 50Hz AC power  
superimposed on the trace. Presume this was due to the SM power supply in the  
computer being held above ground at RF with the power input filter network. An  
isolation transformer offered a total cure. Yours is a different  type of
problem, but the isolation of the two devices may help. Found  a later lap top
computer also with a SM PSU gave similar spike problems. Don,  W3FPR offered advice
at the time to recover this type of transformer from  redundant PC modem
cards.
 
Bob, G3VVT
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