[Elecraft] K2: KSB2 T1/T2 Turns Ratio Question

[John Magliacane]

Hi Don.

Thanks for the reply.

>  John,
> 
> I cannot answer your exact question (the impedance ratios), but I need to ask a
> question about your "narrower than expected" filter response.

I plotted a sweep of my TX chain a number of years ago, the results of which can be seen here:

       http://www.qsl.net/kd2bd/sweep2.png

It's a linear plot, so the ripple and other imperfections really stand out.  It was taken by sweeping audio through the KSB2 well below the level of ALC action while measuring the corresponding audio level picked up by a nearby crystal controlled, direct conversion receiver having no filtering or AGC.

Looking at the red LSB curve, if we estimate the center of the passband to average around "70" in amplitude, -3dB would be around "50", and -6dB would be around "35".

>From this, I estimate the -6 dB bandwidth to be around a 2.2 kHz.  And this is with the 2.5 kHz -3dB bandwidth (2.6 kHz -6 dB bandwidth) coupling capacitors in the ladder.

And, lastly (although less scientific), if I optimize my CAL FIL settings so that my transmitted audio has the identical quality on LSB that it has on USB (as observed on a wideband receiver), my BFO settings are only 2.3 kHz apart.  This is 400 Hz less than the spacing suggested in the KSB2 instruction manual for a 2.2 kHz (-6 dB) bandwidth.


73, de John, KD2BD
K2/100 #3563