[Elecraft] K2 TX Excessive Low Frequency Audio Response

[Stewart Baker]

Hi,
There seems to be some confusion about ways to improve the K2 
transmit audio. To get the best results it is necessary to make 
sure that all parts of the transmit chain are optomised. 

1) Use a good microphone (not necessarily the most expensive), 
that has a well defined frequency response, and suits your voice.
You can verify this off-air by using a tape recorder or Windows 
audio recorder.

2) Accurately align the KSB2 filters. This procedure has been 
described many times on this forum, and in the Builders help 
pages. Use Spectrogram or WaveSpectra programs (both free) and 
spend some time getting the received frequency response correct.
The 300Hz point on both USB and LSB should be -3dB down. 
Make sure that you are happy with the result, and that your 
friends do not sound like Martians !

3) Listen to your SSB on another receiver with the K2 on dummy 
load, and the transmit power turned right back. The problem with 
this method is that if you use headphones they will have their own 
frequency response that will colour your impression of the 
transmitted signal. Better still get someone on-air who knows your 
voice, and can give you accurate feedback to listen .

4) It is possible that the transmission may sound "boxy" and 
rather lacking in highs. If your K2 sounds perfect on receive then 
LEAVE THE FILTER SETTINGS ALONE. The problem is an TX audio
one not an RF one. ALL elements in the transmit chain contribute 
to the quality of the audio, not just the filters settings. 

Have a look at this page on my web site.
http://homepages.nildram.co.uk/~baker/K2_SSB_Mods_Overview.html

If you really want to be adventurous you can download (free) from
http://audio.rightmark.org/index_new.shtml and plot the actual 
audio response of your KSB2.

So in summary, to get the frequency response right:-
a) Your voice (can't do much about that !)
b) Mic with tailored frequency response.
c) Accurately align the KSB2 filters on receive USB & LSB
d) Listen to the result, and get reports
e) If lacking in "top" or too muffled, change coupling capacitors.

Hope that helps..
Very Merry Christmas to all.

73
Stewart G3RXQ