[time-nuts] 10 MHz -> 16 MHz clock multiplier
Bob Camp
lists at rtty.us
Sat Jan 5 00:48:14 UTC 2013
Hi
As I recall the spec was:
1) Cheap
2) no phase slips on the 16 MHz relative to 10 MHz
3) Cheap
Bob
On Jan 4, 2013, at 7:18 PM, EWKehren at aol.com wrote:
> How about getting back to basics.
> Is it a one off, if production how many and what are the specification
> requirements? Otherwise on this list it can go on for a year.
> Bert Kehren
>
>
> In a message dated 1/4/2013 6:11:14 P.M. Eastern Standard Time,
> wlfuqu00 at uky.edu writes:
>
> At 07:51 PM 1/4/2013 +0000, you wrote:
>> My question is about the phase noise of the final 16MHz signal. Do
>>> crystal filters "clean up" the signal. It seems that after several
>>> 16MHz crystals in series the output should look a lot like an XO.
>>>
>>
>> For offsets out to 100 Hz or so, using a crystal filter will cause
>> the signal to have the same flicker noise that an oscillator built
>> with that crystal would have. Thus don't try to use some junky
>> clock crystals to make a crystal filter as described in numerous
>> ham radio articles about receiver IF filters. If you have a
>> residual phase noise measurement system like the Agilent E5505A
>> and a very low flicker noise source, you can actually measure your
>> filter crystals. Of course, the crystal time base in the source
>> has to be better than the crystals you are measuring. You also
>> have to avoid overdriving the crystal. This will require a low
>> noise buffer amplifier to bring the signal back up to a high
>> level.
>>
>> Now after considering all that, crystal clean up filters don't
>> sound like such a great idea unless you have no alternative.
>>
>> Rick Karlquist N6RK
> Flicker noise (1/f ) noise would be introduced by an amplifier and not
> by the filter. I am only suggesting ways to multiply the frequency.
> You could use LC filters or a crystal filter. Using 3 doublers would
> do the job just as well. Naturally if you are concerned about flicker noise
> you could simply make the 2 MHz signal higher in amplitude before selecting
> the 8th harmonic.
> I was not saying your going to clean up a good crystal oscillator with a
> crystal filter. I though you were talking about generating 16MHz from 10MHz
> in a clean way. Using a microcontroller or even most synthesizers
> techniques would make
> it even worse.
> The PTS synthesizers have fairly good phase noise when they use
> frequency multiplication,
> division, mixing, comb generation and filtering on the most part to
> achieve
> low phase noise.
> The later models use a DDS at the lower frequency levels but do have
> greater phase noise
> close to the carrier. In fact in the SGA unit the reference input goes
> thru a transistor ( to distort it)
> and then into a series 10MHz crystal filter so that it can accept either a
> 5 or 10 MHz input.
> The crystal also helps filter out any birdies that may be on the
> reference signal.
> The filter should be fairly high Q since it has 47 Ohm drive impedance and
> 100 Ohm load impedance.
> 73
> Bill wa4lav
>
>
>
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