[Elecraft] KX-1 BC interference on 20m

[Stephen Prior]

Hello Don

I certainly wouldn't want to give the impression that I'm not really pleased
with the KX-1 because it's given me a huge amount of pleasure in a
relatively short length of time.

I think I may have hit upon something- the KX-1 received a knock when
camping and I have now discovered that the knock broke both solder joints
for the ground connection on the bnc socket.  Looking at them they seemed
dry anyway and now they have been resoldered the problem has all but
disappeared.  I'm not looking for a perfect transceiver of course, but the
BC stations were fairly intrusive and if I've got that sorted now then I
shall be happy.

Thanks to all for the advice received!

73 Stephen  G4SJP


On 26/08/2008 00:51, "Don Wilhelm" <w3fpr at embarqmail.com> wrote:

> 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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