[time-nuts] Divider circuit for Rubidium Standard

Bob Camp kb8tq at n1k.org
Sun Apr 26 09:56:17 EDT 2015


I would *assume* that either the 20 or 60 MHz is already a square wave. If they both are, use the 20, if not use
which ever one is a square wave already. 

Past that it is just a divide by 2 or a divide by 3 followed by a divide by 2. You want the last stage to be divide
by 2 so the output is symmetrical. 

One of a multitude of possible divide by 3 circuits:


The divide by 2 would just be a D F-F with the inverted output tied to the D input. 

I would build it out of whatever fast modern logic is available. My preference would be for a +5 supply coming 
off of something like an LT1763 linear regulator. Buffers up the outputs with several inverters in parallel. 

Yes it’s not the ultimate super duper circuit. Done properly it will be about 100X lower noise than your 
Rb at Tau <= 10 seconds. 


> On Apr 26, 2015, at 6:51 AM, Bryan _ <bpl521 at outlook.com> wrote:
> All:
> Picked up a FE 5680B from Ebay awhile back. Appears to work fine, but is limited to a 1pps output. However there is a point on the PCB that's documented that has a 20Mhz output. There is actually a clean 60Mhz output as well.
> http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7
> I would like to tap this 20mhz output and feed it to a divider/buffer circuit for a 10Mhz output at 50ohm. Can anyone recommend a good schematic for such a purpose. I was looking at the project from David partridges web site http://www.perdrix.co.uk/FrequencyDivider/index.html
> Cheers and thanks in advance.
> -=Bryan=- 		 	   		  
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