[time-nuts] Divider circuit for Rubidium Standard

Bob Camp kb8tq at n1k.org
Mon Apr 27 07:48:05 EDT 2015

```Hi

Take a look at how the 60 MHz is generated. I believe that you will find that you have a sine wave that has come out of a logic gate via a low
pass filter or that they square it up on the board already.

My *guess* is that you could fit a little board with a divide by 6 into the Rb and run it off of the device’s internal supplies. You would then have
a 10 MHz unit.

Bob

> On Apr 27, 2015, at 5:34 AM, Bryan _ <bpl521 at outlook.com> wrote:
>
> Bob:
>
> The output of the 60 and 20 MHz are sine waves. The 60MHz is very clean whereas the 20Mhz is not. The ebay link has picture of the outputs and they mirror my results. Thanks for the tip on the LT1763, probably better to use a modified schematic of the one I posted and modify the circuit as I don't need all the dividers, but it has the circuitry for the amplifiers and buffers as well "wave shaping" the input.
>
> Cheers
>
> -=Bryan=-
>
>> From: kb8tq at n1k.org
>> Date: Sun, 26 Apr 2015 09:56:17 -0400
>> To: time-nuts at febo.com
>> Subject: Re: [time-nuts] Divider circuit for Rubidium Standard
>>
>> 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 it’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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