Hi,
Let's do the math. The K3(S) has an IF frequency of 8.215MHz. So when you
listen to, say, 21.4, the synth is generating 21.4 + 8.215 = 29.62MHz.
Multiply this by 3 and add the 8.25.MHz and you get 97.06MHz! The K3's mixer
has a *very* strong response to the 3rd harmonic of the LO since it is
essentially a square wave. The responsibility for removing this spur is
entirely with the HF filter which evidently does not have enough suppression
to totally reject this extremely strong signal. Do you have the tuner in the
K3? Turning it on would probably help since it is low pass in nature. An
external auto tuner should also help. Your ICOM radio probably is an up
conversion radio so would not have this particular problem (responding to
odd harmonics of the LO).
AB2TC - Knut
W9RE wrote
> I have had an interference problem on the top part of 15 meters (21380 to
> 21450) from an FM station 1 mile from my house whose frequency is 97.1Mhz.
> It peaks about S6 and is quite noticeable with only coax connected and no
> antenna selected. I have (2) -K3 and it is present on both. I installed
> new synth boards in one but the interference is still there. It sounds
> like
> a very broad FM signal. I had the station engineer do a spectrum search
> and
> he found no issues. I do not find this interference on an Icom radio.
>
>
>
> Has anyone else experienced this and if so have you found any solutions?
> I
> did a check of just the K3 (a year or so ago) on battery power and no
> other
> connections and it was still present although much weaker.
>
>
>
> Thanks,
>
>
>
> Mike W9RE
>
>
> <snip>
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