[Elecraft] K2 SSB adjustment

[Marteinn Sverrisson]

All K2'ers

When aligning SSB filters be ware of the low freq cutoff in the audio
chain if you are measuring across the loudspeaker terminals.

The original RX audio low freq. cutoff (-3db) freq. is approx. 640Hz 
(with KAF or DSP moduls installed) 
or 400Hz (with no audio moduls). The cutoff is
determined by C25, C26 (on the control board) and the 5kOhm volume control pot 
(and NE612 mixer output impedance with no audio moduls),

C25 and C26 are 0.1uF each and in series with the vol pot which is 5k. 
This is a high pass filter with abt 640Hz cutoff.
So if you are using Spectrogram og Baudline to adjust the low freq
points, you will not get the correct setting if you do not know this.

To improve the RX low freq range you should change C25 and C26 to 0.22 or
0.33 uF. This affects only the RX audio, and it makes the SSB sound better.

In my K2 I put 0.1uF SMD's across C25 and C26, extending the low frequency 
response to approx. 320Hz. 
It also helps with SNR when copying low pitch CW signals. 

just my $.02

73, TF3MA, Matti

K2 #2024
-- 
   Marteinn Sverrisson    TF3MA
          Langitangi 2    Internet: tf3ma [at] raunvis [dot] hi [dot] is
        270 Mosfellsbær   http://www.raunvis.hi.is/~tf3ma
               Iceland