[Elecraft] K3 and CW-Skimmer

[Arie Kleingeld PA3A]

Bill,

BTW, it happens also when switching from 400 to 2100  (both zero offset).

 From the earlier explanation I remember that the side of the filter BW 
is placed on the side of a signal. (I donot know how to say it a better 
way). The filter is not placed symmatrically.
So when changing the filter, and also when I change the shift, the 
CWskimmer display moves..

73
Arie PA3A

Op 23-2-2011 14:43, Bill W4ZV schreef:
>
> 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
>