[Elecraft] K2 filter response question

[Rolf Moberg]

Hello!

I have been thinking my K2's filters. I worked EARTTY today. Look for 
the following pictures. K4GMF is transmitting around 1000Hz. There is an 
unnecessary extra audio peak around 2.5 to 2.8kHz

http://ugly.blerp.org/~oh6kxl/350Hzfilter.jpg
http://ugly.blerp.org/~oh6kxl/350Hzfilter2.jpg

When tuning so that RTTY  signal is between the 500Hz and 1000Hz you can 
see the extra signal has bigger shift than the original! Same phenomenom 
is visible in all filters.

Next picture tells you what is the filter response with no audible or 
visible rtty signal.

http://ugly.blerp.org/~oh6kxl/350Hzfilter_no_signals.jpg

 From where this unwanted audio peak about 1.6kHz up from actual 
transmission frequency is coming from?

- K2's rx is generating it?
- My Sound Blaster is generating it?
- My cables are generating it? (PC is opto-coupled and galvanically 
isolated from K2)

I have done my filter adjusments with this gMFSK software.

Rolf Moberg
oh6kxl