[time-nuts] Divider circuit for Rubidium Standard

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

```Hi

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:

http://www.indiabix.com/electronics-circuits/divide-by-3/

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

Bob

> 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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