[Heathkit] HR-10 Improvement on 10/15 ?

[Drew P.]

Paul wrote: 
> I have an HR-10 that I am restoring to work with my DX-60.
> Like most 
> (all) HR-10's it is deaf on 10M and 15M. This appears to be
> due to 
> the scheme of using the 2nd harmonic of the oscillator on
> those. 
> bands. The trouble is that there is not very much second
> harmonic.
> 
> So I was thinking of adding a FET buffer to the output of
> the 
> oscillator to generate some harmonics. Unfortunately a
> simple clamp 
> would generate a square wave which only has odd
> harmonics.  A 1/4 
> width pulse train generates a healthy 2nd harmonic, and
> maybe could 
> be implemented.
> 
> Any thought on this or other ideas to improve the second
> harmonic?

A "lopsided" clamp (1 diode) or other scheme which adds asymmetry to the oscillator waveform would increase second (and higher order) harmonic content.  You might try a BJT or FET amplifier stage - run it to clip one one peak of the waveform.  Or, you might sidestep the issue completely with an RF preamplifier ahead of the receiver.  If a preselector, you'd also improve image rejection.

Drew