[Elecraft] RE: K2 Keyer Problem

[G3VVT at aol.com]

In a message dated 11/04/05 13:52:21 GMT Daylight Time, reberhar at iupui.edu  
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