[Elecraft] K3 IF Design

[Shane White]

When considering the differences between the K3 and IC-7800/7700/756PRO3 or
FTDX-9000/2000, apart from the K3's lack of band-scope, numerous large knobs
and colour screens, the other thing that stands out is the selection of the
1st IF frequency.

Most other radios use a VHF 1st IF (typically about 70MHz) whereas the K3
has been designed to use 8MHz. Icom and others point out that a VHF IF
allows their radios to obtain superior image rejection. This is done at the
expense of non-ideal filter bandwidths though, as it's difficult to design
narrow filters at around 70MHz. I think the K3 manages to provide 1st IF
filter bandwidths of just 400Hz doesn't it?

Does anyone have a useful link to the definition of image rejection?

Does the K3 manage to obtain image rejection comparable to Icom's and
Yaesu's flagships? If so then it seems to me that Icom and Yaesu seem to be
relying on a proven RF design and instead are concentrating their current
efforts on ergonomics and presentation. There's nothing wrong with that
though.

Thanks,
Shane
VK5ABQ
South Australia.
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