[Elecraft] Crystal Filter Offset in 4.81, What does it mean?

[Arie Kleingeld PA3A]

Don,

I understand this.

Let me explain my thoughts.
Let's suppose we have the different IF's. One analog, the 8Mhz stuff, 
and then a "DSP IF" which is fed by the second 15kHz IF.

I am not a DSP expert. But I would expect that the DSP filter would 
filter out whatever bandwidth I would want it to, just like it were 
analog and better. I expect this function of any IF filter, digital and 
analog.
What we are tallking about is that the opposite sideband can pass 
through the analog part of the K3 (because of the wide roofing filter) 
and yes it does if the skirt of the filter allows it. If this is not 
solved in the DSP, the /function/ of the DSP is not more than the old 
type audio DSP filter we had in the old days (apart from partly being 
inside the AGC-loop)

As Ralph DL5OAP already stated: Even the old FT1000MP with DSP 
demodulation killed the opposite sideband. I had an MP for a long time 
(before I got the K3) and I can confirm this. I had it switched on all 
the time.

As you said Don, the K3 really needs the analog roofing filter to be in 
place to reach its best performance. Good thing that I have them for the 
bandwidths I use. And overall it works pretty well. There are still some 
things to improve though.

73
Arie
(not Arnie  :-))


Don Wilhelm schreef op 6-2-2014 17:21:
> Arnie,
>
> Think about it this way -- take a filter width of 1500 Hz and a 
> sidetone pitch of 600 Hz.
> If you center the passband at 600 Hz, the upper passband limit will be 
> at 1350 Hz, but the lower edge will be 150 Hz into the opposite 
> sideband (single signal reception goes "bye-bye").
>
> The proper position if the passband is to place the lower edge at 
> about 100 Hz, and the upper edge will extend to 1600 Hz.
>
> That is true for any passband that is greater than 2 times the 
> passband width.
>
> 73,
> Don W3FPR