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

[Paul Baldock]

The project is now complete with the following results:

S9 reading:
29.0MHz -72dBm (56uV)
21.3MHz -66dBm
14.2MHz -72dBm
7.2MHz -73dBm
3.8MHz -72dBm

1uV on all bands just lifts the S-Meter off zero. A .2uV signal is 
detectable by ear.

I built a balanced broad band frequency doubler with 2 MPF102 FETs, 
and tweaked it slightly off balance so that the fundamental and 
second harmonic were about the same amplitude. I preceded the double 
with a MPF102 fet buffer to limit the oscillator loading. I followed 
the doubler with a low impedance buffer using a 2N3866. This is all 
powered by a voltage doubler/rectifier off the filament supply.

I also stabilized the Oscillator with a 130V zener. This eliminated 
the varying frequency with AGC level or RF gain.

I also rewired the BFO to use a FET rather than a triode, this gave 
me better control of the injection level.

- Paul  KW7Y



At 08:51 AM 11/27/2011, you wrote:
>Paul wrote:
>
> > 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.
>
>Part of the solution may be also increasing drive to the mixer at 
>the oscillator fundamental frequency.  This would cause more 
>harmonic generation within the mixer itself. A combination of this 
>and external harmonic enrichment via an added 
>asymmetrically-clipping buffer stage might be used.
>
>You could try reworking the oscillator to run at the correct 
>injection frequency (not at a subharmonic), but this probably would 
>have more than its share of problems, else Heath would've designed it that way.
>
>Drew
>
>
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