[Elecraft] DSP Filters

[Tom Hammond]

Hi Pierre:

At 11:26 AM 1/27/2006, you wrote:
>A question about DSP... I did not find any indication about the 
>exact sequence of filters display in DSP.
>
>For instance, lets say that we select CF2 and the tap XFIL; then, 
>the display shows an FL filter. But I am not sure that it is one. If 
>I go through until I get FL1, it does'nt like the normal FL1 that I 
>have. Especially if the denoiser was ''on'' in DSP. As I understand 
>it, the xtals filters are changing the IF (RF) bandwidth and the 
>DSP's ones are doing the same thing, but on an audio range after 
>digitization. Since I have set the same bandwidths for each group 
>(i.e. FL2 like CF2, FL3 like CF3...), the difference is not always apparent.
>
>So, how to toggle between the cristals and DSP filters with a 
>correct display of the set choosen?

The two filters (Xtal and DSP) work independent of each other, BUT 
they MUST both be aligned on the SAME CENTER FREQUENCY (SIDETONE).

If you have FL1 AND CF1 both set to 400Hz bandwidth, you may not 
notice a significant change when both are selected, though the 'skirt 
selectivity' should be improved because the slope (shape factor) of 
the DSP filtering is sharper than that of the XTAL filter.

Where the DSP shines is at bandwidths of <200 Hz. The K2 XTAL filter, 
when set to 100Hz, in not significantly more narrow than when it is 
set to 200Hz B/W, but it will exhibit somewhat more signal loss. As a 
result, consider using a 200Hz B/W for your most narrow XTAL filter, 
and then using the DSP to obtain more narrow bandwidths, of say 100Hz 
and 50 Hz.

Hope this helps a bit.

73,

Tom Hammond    N0SS