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

[Wes (N7WS)]

Actually, the crystal filters have two purposes:

1) Eliminate the 15 KHz  image that would otherwise be a problem

2) As Don said; however, it's the 2nd mixer that needs more protection than the DSP.

Wes  N7WS

On 2/6/2014 11:38 AM, Don Wilhelm wrote:
> Arie,
>
> Sorry about the added "n".
>
> Yes, the DSP algorithms will not allow the passband to extend into the 
> opposite sideband.
> What I was responding to was the initial statement about "centering" the 
> passband (on the CW sidetone pitch), and I was pointing out the fallacy of 
> that when the filter is wide.
>
> The analog filters at the 8 MHz have only the task of keeping strong nearby 
> signals out of the ADC and not overloading it - they also reduce the exposure 
> of 'pumping' for the hardware AGC by those strong signals near in frequency 
> (such as may be encountered in a DX pileup or contest conditions).
> The DSP does the final filtering, and the DSP filters do not actually need the 
> roofing filters at all other than for the reasons stated above.
>
> 73,
> Don W3FPR
>