Stephen and Ed,
I was thinking along those same lines. On 20 meters, the KX1 LO signal
is below the RF signal, so a strong BC station in the 4.1 to 4.3 MHz
range could push itself through and be heard on the upper end of the 20
meter band. If you have no stations on that part of the spectrum, you
can likely reject the assumption of an image response.
The KX1 design faced many challenges in order to stuff all that
performance in a small space, so the design is a bit of a compromise.
The front end suffers from responses in the presence of strong RF energy
just like any other Gilbert cell mixer connected in the receiver front
end (with no RF amp stage for isolation). My understanding is that the
Gilbert cell mixer can generate 'funny stuff' in the presence of strong
RF energy fields like might be found in Europe - in reading EMRFD, I
find that Wes Hayward does not even recommend the gilbert cell mixer for
use in receivers that will be used on the Eastern side of the US for
this very reason.
In addition, the DDS does have some spurs that can be mysterious - if
the offending signal tunes more quickly than normal signals, you are
likely hearing the result of one of the DDS spurs.
The KX1 is a good design, but it just is not perfect in all ways. You
may be hearing the result of one of these imperfections - OTOH, you
*could* have a problem there. Comparison with another KX1 under the
same circumstances is one way of telling whether a problem exists or it
is just one of those design compromise situations.
73,
Don W3FPR
Ed - K9EW wrote:
Hi Stephen,
It might help if you could identify the SW stations you're hearing,
and find out what frequency they're on. What you could be hearing is
a very strong signal on the receiver's image frequency, and the only
thing you could do would be to add more selectivity to the front end
to attenuate the signal on the image frequency. Ask Elecraft, they
would know.
73,
ed - k9ew
www.k9ew.us\
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