[time-nuts] 10 MHz -> 16 MHz clock multiplier

EWKehren at aol.com EWKehren at aol.com
Sat Jan 5 00:18:40 UTC 2013


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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