Re: K2 BFO Drift / Filter Alignment

Posted by K1FFX on Jan 05, 2011; 8:32pm
URL: http://elecraft.85.s1.nabble.com/K2-BFO-Drift-Filter-Alignment-tp4236424p5893450.html

I'm wondering if there was any resolution to this problem, first posted just over a year ago,
since I observe what I think is the identical problem with my K2 S/N 6982.  A related
symptom was obvious BFO shift when pressing down on the top cover just behind the
A=B push button (for example, to hold the K2 steady while turning off AGC or checking
current XFIL setting, i.e., an operation that requires two button pushes).  Some loosening
and moving of the side panels seems to have resolved this second symptom, but the
BFO shift out of the filter center frequency persists.

I'm currently working on KPA100 construction, and would really like to resolve this
before installation (still several days away ... now looking at T1 installation!) and
would appreciate any thoughts on this BFO shift.  Meanwhile, have started tracking
BFO freq/Pin 14 voltage per Don's suggestion.

Thanks!

- Bruce

Don Wilhelm-4 wrote

I do have a suggestion - make a series of tests over a period of several
days before doing anything to try to fix it.
You think the BFO is shifting, so find out for certain.  Take one filter
that you are not likely to use (like LSB FL4), and do NOT change that
one.  Instead, select that filter,  enter CAL FIL, tap BAND-, then tap
DISPLAY to see what the BFO frequency is.  Record the BFO frequency over
a period of days and see whether it really is changing.  At the same
time you make the frequency reading (and without changing filters)
record the VBFO signal voltage - that can be found at Control Board U10
pin 14.


73,
Don W3FPR


Douglas Furton wrote:
> I'm having a problem with my K2 (SN 6761 10W/CW only): I have to align the crystal filters almost daily.  It seems the BFO shifts by 200 Hz or more almost daily.
>