[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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