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

[David Larson]

Thanks Paul.  I think I'll give it a try on my HR10B.

73
Dave WB0TSR

On 2011-12-03 19:45, Paul Baldock wrote:
> 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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>