[Elecraft] K2 birdie at 28.265 MHz

[Ron D'Eau Claire]

Michael asked:

Does anyone know what causes this one. I have just about every option  
installed including the KPA100. Would like to get rid of it if possible (S5
on  the 
meter with a 1KHz tone).

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My K2/100 shows it at 28264.50, about S3 with the preamp turned on. The
frequency shifts slightly when the PA is enabled or disabled using the
secondary menu. Seventh harmonic of the 4 MHz oscillator in the KPA100
perhaps? 

The frequency of that oscillator is not critical, but I don't know how far
you can shift it using the trimmer cap. 

Ron AC7AC