[Elecraft] K3: Optimizing filter offsets for SSB TX and RX

[Joe Subich, W4TV]

If I wanted to check for filter offsets in the 8 pole 
filters, I think I would put them into the main RX 
and run response curves (using the K3 Filter Utility 
package) in both USB and LSB (or AFSK A NOR and REV). 
Set the DSP bandwidth to 4.00 and the center frequency 
to 1.50 (SSB) or 2.20 (AFSK A) to minimize the DSP 
contribution to the response.  

One set of data would need to be inverted and offset 
to compare the two responses but one could overlay 
the two curves and look for any asymmetry ...  I would 
check specifically to see if the -3 dB points were 
spaced equally above/below the center frequency. 

The skirts will not be symmetric in LSB/USB due to the 
sharp cutoff near the carrier in USB/LSB (1500 - 1400 
= 100 Hz).  Any offset may be more apparent using the 
AFSK A settings.  

73, 

   ... Joe, W4TV 
 






> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Windy Dankoff
> Sent: Sunday, April 12, 2009 10:28 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3: Optimizing filter offsets for SSB
> TX and RX
> 
> 
> YOU ARE RIGHT, Joe !!  I did my trials on USB. On LSB, I can tell by 
> listening and re-adjusting that you are quite correct. It's back to
> zero for me.
> 
>     :-|
> 
> I await further comments.
> Windy
> 
> 
> On Apr 12, 2009, at 5:10 PM, Joe Subich, W4TV wrote:
> 
> >
> > If you crank in an offset with the 8 pole filters be sure you test
> > it with BOTH USB and LSB.  An offset that enhances low frequency 
> > response in USB will reduce the LF response in
> LSB (enhance
> > high frequency response) and vice versa.
> >
> > 73,
> >
> >   ... Joe, W4TV
> >
> >>
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