[Elecraft] [K3] Questions about ARRL review

[Don Wilhelm]

Doug,

I have never seen a crystal filter that is truly symmetrical.  That is 
just the "facts of life".  The real question is, just how much asymmetry 
is the user willing to tolerate.  Since this is a roofing filter, and 
not the ultimate filter for the K3, I tend to believe that the 5 pole 
filter is adequate for my purposes.  YMMV.

73,
Don W3FPR

Douglas G. Bonett wrote:
> Table 2 of the ARRL review finally answered my questions about the relative
> performance of the 2700 and 2800 Hz filters at 1 Hz and 2 Hz spacing. The
> results are very impressive. Can someone explain to me why the above/below
> results for these two filters are so disparate at these narrow spacings?  The
> review suggests that the observed asymmetry is quite unusual. Is the performance
> of a radio most accurately described by the larger or the smaller of the
> above/below values? Is the asymmetry due to a design problem in the roofing
> filters or something in the K3 circuitry? If the asymmetry could be corrected by
> a change in roofing filter design, would the above/below values both become
> similar to the average of the two values? For instance, would the 94/81 IMD
> values at 1 kH spacing for a redesigned 2800 Hz filter approach 87.5/87.5, which
> would be a truly spectacular result for a radio with a single 2800 Hz roofing
> filter. 
>   
>