[Elecraft] K3 #8862 unwanted sidebands

[Wes]

The K3 has a built-in two-tone generator.  I've done 100s of two-tone IMD tests 
on my K3 and K3S using them and an SDR-IQ as a spectrum analyzer.

Wes  N7WS.

On 11/15/2022 11:37 AM, Michael Carter wrote:
> Hi Martin,
>
> Do you observe (or hear) sidebands outside
> the nominal transmitted bandwidth with
> CW transmissions or only SSB transmissions?
>
> Can you perform a 2-tone test with an
> audio source other than speech?
>
> The fact that the unwanted sidebands
> are not observed when the KPA3 100
> watt amplifier is bypassed suggests
> a possible change in the bias point of
> the PA transistors.  If you have the original
> BJT version of the KPA3, not the LDMOS
> version of the KPA3A, perhaps you can measure
> the base or collector bias current when the
> KPA3 is engaged (PWR control set at 12 watts
> or above) with no audio modulation applied.
> That may be difficult to do without temporarily
> lifting a component lead.
>
> Perhaps Keith, WE6R from Elecraft can
> suggest a way of confirming proper bias
> point setting for the KPA3 without too
> much intrusion?
>
> 73,
> Mike, K8CN
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