[Elecraft] Filter questions

[Bill W4ZV]

Dave Blaschke wrote:
> 
> I will ask here before calling Elecraft.
> 
> First, I have the following filters installed on the main rcvr, all 8 
> pole: 6 Khz, 2.8kHz, 1.8 kHz, 400 Hz, 250 Hz.
> 
> There are two issues:
> 
> 1. When I turn my 250 Hz filter on in config, and then select that 
> filter (which is FL5 here)I can hear noise coming through but no cw 
> signals come through. I can see the signals on my PowerSDR/LP-PAN 
> setup and CW Skimmer. Signal comes through all the rest of the 
> filters O.K. Yes, I opened the radio, and all the filters are installed.
> 
> 2. I run CW Skimmer with my K3. When I change filters, the CW offset 
> signal shown on CW Skimmer changes. I thought the 8 pole filters had 
> no offset. Is anyone else experiencing this? Any comment appreciated.
> 
> Dave, W5UN
> 

Both issues sound like there could be an offset problem in the 250 Hz
filters.  I only have 5-pole CW filters here but I know Ed W0YK has reported
offsets in his 8-pole 400/250s of up to 80 Hz.  Given that the 250 Hz 8-pole
is actually around 370 Hz wide according to Inrad plots, I don't see how
even an 80 Hz offset could cause the problem you noted in #1 above.  However
I believe most of the 8-pole filters will have the problem in #2 above since
they do not truly have zero offset.  

If I used 8-pole CW filters, I would measure the actual offset and enter it
into the Filter Configuration menu.  This would solve problem #2 above and
it might also tell you whether you have a defective 250 Hz filter causing #1
above.

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