[Elecraft] K2 BFO Test Problems on #4161

[Darren Hobbs]

When carrying out the BFO Test on page 62 of the K2 manual I seem to have
too much BFO range. Although pressing "Band+" gives a stable 4917.53kHz with
about 8V at "V BFO", "Band-" gives a rather unstable 4.5MHz or so with about
0V at "V BFO". The control voltage range is as expected (0 to 8V). It would
appear that the VXO is being pulled beyond the limits where the frequency is
determined by the crystals.

I have rechecked all component values and solder joints in the BFO area and
all are correct. L33 and R116 were removed as an assembly and measured on my
AADE LC Meter IIB: A value of 43uH was recorded - just within the 5%
tolerance, so the component was replaced on the pcb.

I then reduced C173 from 220pF to 150pF and C169 from 390pF to 330pF in an
attempt to reduce the pulling range of the BFO. This had the desired effect:
Band+ giving a stable 4917.5kHz as before and Band- giving a stable
4912.2kHz.

Before I commit these changes to the pcb, I'd welcome comments from other
constructors. I have been trawling the archives to see if this or a similar
problem has been reported before - haven't been able to find anything yet.
The search has revealed though, that a considerable amount of work has been
done on optimising the pulling range and temperature stability of the BFO,
so I'd hate to compromise the performance of the BFO with my modifications.

Best regards,

	Darren

ps I only have email access at weekends so if there are further questions,
there may be some delay in my replies.