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

[Paul Baldock]

Today I substituted a signal generator for the LO and as expected the 
10M and 15M performance improved dramatically (just a few dBs down on 
the other bands). It requires about 6V P/P at the true RF+IF 
frequency. Now to make the internal LO do that.

- Paul

At 11:13 AM 11/26/2011, Drew P. wrote:
>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
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