[Elecraft] K3 and CW-Skimmer

[Bill W4ZV]

Arie Kleingeld PA3A-2 wrote:
> 
> When using different roofing filters in the K3, the IF-offset changes a 
> bit in the K3, if you switch to another roofing filter, if I understand 
> it correctly.. It has been explained in this reflector that this happens 
> for a reason. It has to do with the way the roofing filter is placed 
> over the signal you are listening to. There are experts that can explain 
> what happens exactly. (So some more info is needed please.)
> 
> I was not aware of this problem  untill I used CW skimmer and the N1MM 
> logger bandmap and saw that I had to keep the 400 roofer in place 
> otherwise the spots would be placed on the wrong freq in the bandmap. So 
> that's what happened here.
> 
> I wonder if others have seen this behaviour and what they did about it.
> 

Your understanding is correct.  Each time the K3 changes roofing filters, a
different offset is required for CW Skimmer to zero beat unless (the filters
have identical offsets).  This is one good reason to select all 8-pole
filters since they have identical offsets of zero.  Yes, before someone says
it, I know the 8-pole offsets are not actually zero but it doesn't matter
since the offsets are a small percentage of total bandwidth (even the "250"
which is actually 370.

In contests I use both a 500 Hz Inrad 8-pole and a 200 Hz Elecraft 5-pole. 
For the CQ 160 which is EXTREMELY crowded, I used the 200 Hz 99% of the time
(both for running and for S&P with Blind Skimmer) so I set Skimmer's offset
for the 200 Hz filter offset.  In the ARRL DX, which is not so crowded, I
used the 500 Hz when running (when I don't need a waterfall) but then
adjusted WIDTH so the 200 Hz was activated when using Blind Skimmer to S&P
on the waterfall decoder dots.  Since Skimmer's decoder dots are so accurate
in placing the K3 passband on signals of interest, the simplest thing to do
is to always use your narrowest filter setting for Skimmer.  You could
quickly change this by making Filter Preset I for "normal" use and Preset II
for "Skimmer" use.

Another thing I do is record the two different offsets for Skimmer (for the
500 Hz and 200 Hz filters) and paste it above the appropriate place on my
monitor.  Then I can quickly adjust Skimmer's Setting Menu if I ever need to
change the filter used with Skimmer.

73,  Bill  

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