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

Raj vu2zap at gmail.com
Thu Feb 3 07:02:55 UTC 2011


Thanks Said,

My object of the exercise was to multiply the error of a 10Mhz Rb /GPSDO source
so that I would get 8x phase error between two compared frequencies. 
This I presume would make adjustments of my sources much easier.

OTOH, if we lock 80Mhz to Rb source and use that as a clock for the Super
DDS 2 VFO kit, then I would have a pretty good HF signal source.
http://www.pongrance.com/super-dds.html

Cheers
Raj, vu2zap


> 
>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
>
>
>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
>




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