So I decided to open up my K1 and recheck the 30-meter bandpass filter alignment, guessing that the simple “peak coils for maximum” in the manual might also tend to peak the spurious emissions for maximum as well. Sure enough that was the case. I was able to find coil settings that favored a lower 6th harmonic value without negatively impacting the output power.
In the above graph, there was 40 dB of external attenuation. So the carrier on 10.120 MHz is 40-6.90 dBm, or 33.1 dBm (which is 2 watts — the value used for alignment). At this setting, the greatest spur was the 6th harmonic, and it was -49.1 dBc, a passing value.
Life is good!
