[time-nuts] Fwd: 10MHz to 80MHz frequency multiplier suggestions

SAIDJACK at aol.com SAIDJACK at aol.com
Wed Feb 2 20:12:38 UTC 2011


 
Hello Raj,
 
our ULN-1100 and ULN-2550 GPSDO's use a 100MHz VCXO locked to the 10MHz  
OCXO via an ADF4002 PLL with less than 40Hz bandwidth. After careful  
optimization of the layout and the loop filter, the phase noise results are  quite 
excellent at 100MHz, see the attached plot. The plot shows two versions of  
the PLL loop filter from the design phase of the products, one has been more  
optimized. You can see that the noise floor is almost -170dBc/Hz at  100MHz.
 
You get the best of two worlds: the absolute frequency accuracy of the  
GPSDO, and the very low phase noise of the VCXO above the PLL bandwidth. It is  
clearly visible that the VCXO phase noise inside the loop bandwidth is 
actually  also reduced by locking it to the 10MHz OCXO (the PN curve below the 
loop  bandwidth frequency of ~30Hz would just continue going up without the  
PLL)
 
Low Noise 100MHz VCXO's are readily available at mouser  and digikey (so 
are 80MHz units), and programming the ADF4002 is  straight forward with the 
help from the AD online tools. It can be bit-banged  with any microcontroller.
 
bye,
Said




From: Raj <_vu2zap at gmail.com_ (mailto:vu2zap at gmail.com) >
Date:  January 31, 2011 21:11:46 HST
To: Discussion of precise time and  frequency measurement 
<_time-nuts at febo.com_ (mailto:time-nuts at febo.com) >
Subject:  Re: [time-nuts] 10MHz to 80MHz frequency multiplier  suggestions
Reply-To: Discussion of precise time and frequency  measurement 
<_time-nuts at febo.com_ (mailto:time-nuts at febo.com) >





I was contemplating the same thing. I fed the output to a bifilar  
transformer and 
diode doubler and got good results. I have  to add an amp and double it 
again twice
more. It is still on  breadboard. The object was to multiply the error 8x 
and  compare.

Probably a PLL locking to 80 Mhz  will retain the long term accuracy of the 
TBolt  reference.

Raj,  vu2zap

At 31-01-2011, you wrote:

I'd like to convert the 10MHz output of a  Thunderbolt to 80MHz: it should 
be


used as a 3.3V clock for an A/D  converter.


Even if I have already taken a look to  documentation from KO4BB and Wenzel


regarding frequency  multiplier,


I'm asking if you have some more references  or even better, some schematics


of a working 8x  multiplier.





.     thanks in  advance


_  Elio  Corbolante.



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