[Elecraft] [K3] Questions about ARRL review

[Douglas G. Bonett]

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. 

Doug N0HH  (K3/10 #1213)