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

[Rob Doyle]

On 11/25/2011 1:20 PM, Paul Baldock 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?
>
> Thanks
>
> - Paul

Are you trying to increase the conversion efficiency of the harmonic or
amplify harmonic that is present?

An RF Transformer with a CT secondary and a pair of diodes - arranged
like a full wave rectifier is a standard way of building a frequency
doubler with 10-15dB conversion loss.

Minicircuits is a good source for passive frequency doublers, if you
don't want to roll your own.

http://www.minicircuits.com/app/DOUB9-2.pdf

Rob.