[Elecraft] K2 Temp. compensated PLL mod

[Eric Swartz WA6HHQ - Elecraft]

Yes the BFO toroid mod does alter the relationship between the DAC numbers and 
the actual BFO frequency. The inductor the toroid replaces impacts what 
frequency the BFO oscillates at. A slightly different value inductor (the 
toroid) will change the natural frequency of the oscillator, requiring a 
different varactor voltage (controlled by the DAC voltage) to reach the same 
operating frequency.

Always write down your filter BFO frequencies, not the DAC numbers.

Also don't forget that the BF1t frequency also sets the SSB transmit audio 
range and that a very small change in this parameter (+/-100 Hz) can make a 
big difference in the quality of your transmitted SSB audio. (There is a 
different BF1t setting for USB, LSB and Data modes.)

73, Eric  WA6HHQ
----

Larry - WA2DGD wrote:
> Hello all,
> 
> Yesterday I did the BFO Toroid and PLL Xtal upgrade and the Temperature
> Compsensation Mod to K2 #`1672.
> The first step is to write down all the filter BFO frequencies. Well instead
> of recording the actual frequency, I always record the 3 digit BFO control
> parameter. I did the mods, all went well, and then I re-entered my BFO
> control parameters.
> Well I had quite a surprise.. USB was receiving LSB and vice versa, and CW
> sounded like a direct conversion rcvr, I heard both sides of the cw signal
> and my filters were totally screwed up.
> Rather than going into a complete panic, I pulled out the KSB2 SSB manual
> and entered the BFO Frequencies given in the manual as a starting
> point.....everything went back to normal and I was able to use spectrogram
> to set up my filters as before...now my K2 works great again.
> 
> My question is this... do these mods alter the relationship between the BFO
> frequencies and the BFO control parameters? After the mod, my BFO control
> parameters are significantly different than the pre-mod numbers. The K2 is
> working great but I'm curious as to what happened.