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

[David Larson]

Looks like pretty good results Paul.
Would care to share a schematic of your changes ?

73
Dave WB0TSR

On 2011-12-03 19:08, Paul Baldock wrote:
> 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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