Rolf,
Yes, re-do CAL FIL to properly reposition the filter passbands - the BFO
controls that positioning, so any change in BFO frequency will cause a
shift.
You should not need to run CAL PLL since the PLL reference oscillator has
not been changed.
Why does adding a capacitor change the frequency? The BFO is actually a
VXO, and the frequency is controlled by changing the capacitance in the
circuit - normally that is done by changing the voltage on the varicaps, but
since your total capacitance range was slightly out of normal a small padder
capacitor needed to be added.
73,
Don W3FPR
> -Original Message-
>
> Hello!
>
> After few weeks building incativity due to hot summer I'm back in my
> shack. My K2 #4759 has been on the air several months. However, BFO
> lower limit frequency didn't meet the required 4912.7 kHz
>
> Leigh, WA5ZNU sent me a mail which he had got from Gary from Elecraft.
> Gary adviced to add 1-4pF NP0-capacitor to junction of X3 and X4. I mean
> the lower junction in schematics. That is connected to L33. I added
> 1.5pF NP0 capacitor on the bottom of the RF board. Other pin of
> capacitor was soldered to ground pad of X4.
>
> BFO is now working OK. You can find the new frequencies below. Original
> frequencies are shown in the brackets.
>
> BFO High Freq. 4917.17 kHz (4917.23 kHz) must be >= 4916.3 kHz
> BFO Low Freq. 4912.50 kHz (4912.95 kHz) must be <= 4912.7 kHz
>
> I'd be interested in the technical report why adding a little cap to the
> paralleel of L33 and series with parallel connected crystals lowered the
> oscillator frequency. I'm not an engineer. But I'd like to understand.
>
> Should I make CAL FIL (and CAL PLL) again after this mod? I assume they
> are not needed.
>
> Rolf Moberg
> oh6kxl
>
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