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

[Paul Baldock]

Hand scratched schematic here

http://myplace.frontier.com/~paulbaldock/camano/Files/HR-10%20LO%20Doubler.jpg


- Paul


At 05:22 PM 12/3/2011, David Larson wrote:
>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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