[Elecraft] K2 filter alignment problem

[Don Wilhelm]

Richard,

Try widening the FL4 filter out to 0.2 instead of 0.1.  With the more 
narrow setting there is often more attenuation with little actual 
reduction in width.

When aligning the BFOs, pay attention to the DAC values (and/or 
frequencies).  The ones for CW must be less than the filter center and 
those for CWrev must be greater than the filter center.  Normally the CW 
FL4 will have a BFO frequency near 4913.12  and for CWrev a frequency 
near 4914.3 kHz.

Make certain when aligning the filters with Spectrogram you use a source 
of wideband noise.  If you are using 'antenna noise', be certain there 
are no signals nearby.

73,
Don W3FPR

On 4/10/2019 9:28 PM, Robert G Strickland via Elecraft wrote:
> I have aligned my K2 crystal filters with Spectogram many times, but 
> this time I've run into a problem that I can't figure out.
> 
> Using Don's [and the manual's] instructions, I can align F1,F2,F3 in 
> decreasing bandwidths. All works as per expectations. On F4, the 
> alignment goes "ok," [as per Spectogram] but when I use it with 
> on-the-air signals, the signal "disappears" and shows up about 900 cps 
> lower and in "reverse" orientation [BFO on opposite side]. When the 
> signal disappears, I can change filters [F1/F2/F3] and it's right there 
> where it should be with the bandwidth getting narrower as expected. But, 
> switching to F4, it's gone. I have tried changing the BFO frequency 
> throughout its whole range when in F4, thinking that I've aligned it on 
> the "wrong" side. No luck. I'm stumped. Any and all suggestions welcomed.