[time-nuts] 5>10 doubler

Gerhard Hoffmann dk4xp at arcor.de
Wed Jan 28 08:08:22 EST 2015

Am 28.01.2015 um 00:59 schrieb Alberto di Bene:
> On 1/27/2015 11:57 PM, Bruce Griffiths wrote:
>> /The only viable solution is to use better filtering of the output of 
>> a switching multiplier./
> What about filtering the doubler output with a 10 MHz xtal ?
> 73  Alberto  I2PHD
In a correctly designed oscillator, the close-in phase noise
is determined by the crystal only and it's generally accepted
that there are 20 dB differences from a single batch. Our
data support that. Only 10% are really good.

If you filter with a crystal that is in resonance it will impress
its own phase noise on the signal-to-be-filtered, and the odds
are that you lose.

Also, crystal dissipation should be only in the 100s of uW max.
Using it to filter a 10 dBm signal probably will do harm.

It is a different game when you want to notch away sub/harmonics.
The power levels of the harmonics are much lower and the
crystal does not resonate on the resonator frequency. If you
mis-tune a trap, it won't deliver its notch but it will leave all other
frequencies alone. A LC series circuit that produces a crater of
15 % center frequency could have more global effects if mis-aligned.

When playing with the notch filters for my doubler I got the idea
that one could use them to filter away sideband noise even at the
16 dBm level. One would have to be careful not to tune a notch
over the carrier, but stay away 100 Hz to some KHz. That might
bring an oscillator from "quite good" to "impressive" over a limited
offset range. I have made a filter board for a dozen notch crystals.
That could be populated with the 90% losers from oscillator production.

There is also an offset generator from JPL IIRC where they divide
100 MHz down to 10 KHz, subtract that from the 100 MHz with a
single sideband mixer and use the 99.99 MHz for a DMTD system.
Here one could use the notch filter array to get rid of the
residual carrier & wrong sideband.  DDS-free.

But I have no time to follow that in the moment. :-(

73, Gerhard, DK4XP

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