Using CWT to determine 8-pole CW filter offsets (was: Shift pitch)

[ni0c]

On 27 Jan., W5UN wrote:

 

"I have three 8 pole filters installed, 2.8, 1.8, and .4 kHz. As I
rotate the WIDTH knob, the filters switch in and out at their
transition frequencies (as they should). But when that switch occurs,
the background noise pitch frequency seems to jump to a different
SHIFT frequency setting.  In other words, the transition between
filters is not smooth.

I am wondering if all K3's with 8 pole filters do the same thing as mine?

My filter offsets are all set to zero, as that is what I am told the
8 pole filters offsets should be."

 

 

I've noticed the same thing happening when transitioning 

from the 250 Hz 8-pole filter to the 200 Hz 5-pole.  This 

morning, I noticed the CWT was a couple of notches to

the left of center whenever the receiver was tuned to an

unoccupied frequency with the 8-pole filter.  (It was on

dead center with the other filters.)  

 

I then used the Elecraft K3 Utility to experiment with

various offset numbers for the 8-pole filter. It only took 

a handful of trials before I came up with a setting of 

-0.09 that resulted in CWT being centered on noise 

and a satisfactory transition with the 5-pole filter.

 

Thanks to Elecraft for the MCU 2.80 firmware that

allows the CWT to remain on all the time.

 

BTW, I really like AA6YQ's DXLab Commander program

for controlling the K3.  Among other nice features. it has

a convenient slide bar for adjusting the DSP width and shift.

 

73,

Chuck Guenther  NI0C

K2/10 s/n 5853

K3/100 s/n 1061       

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[Bill W4ZV]

ni0c wrote

I then used the Elecraft K3 Utility to experiment with
various offset numbers for the 8-pole filter. It only took
a handful of trials before I came up with a setting of
-0.09 that resulted in CWT being centered on noise
and a satisfactory transition with the 5-pole filter.

-0.09 equals 90 Hz offset...very consistent with the ~80 Hz others have measured in 8-pole filters.  This is no big deal for wider 8-poles but would be a noticeable offset for the 400 and 250.

                                   73,  Bill