[Elecraft] K2 drif problems?

[Lyle Johnson]

Hello Tony!

> >This has promise as long as the introduced phase noise is low
> >enough.  One the the K2's reasons for great signals is its
> >very clean oscillators...
>
> Huf-n-puf does not introduce phase noise. It is simply a counter which
> decides whether to gently increase/decrease voltage across a
> varacter which is in parallel with the LC cct of the VFO -
> in this case an xtal.

The original huf-n-puf introduced corrections at about a 10 Hz rate, with
filtering.  For phase noise purposes, this is equivalent to a PLL with a 10
Hz reference.  You will get sidebands at +/- 10 Hz, +/- 20 Hz, etc., so the
filtering is very important.  I have seen plots of frequency lock for
huf-n-puf over the years, but not for phase - but I just downloaded a lot of
additional material I had not reviewed previously and may find some info
there.

The later Fast huf-n-puf circuits have a much higher update rate, which is
like a PLL with a higher reference frequency.  Again, the filtering in the
control voltage to the varactor is key.

With clean power and good filtering, the added noise will be very small.

73,

Lyle KK7P