[time-nuts] Frequency division by 81

[Ole Stender Nielsen]

Dear Gilles,

If I understand you correctly you will take the French time signal at 
162 kHz and divide the frequency with 81 in an attempt to compare two 2 
kHz signals, one originating from the time signal, and another from an OCXO.

However, I would advice not to take the 162 kHz signal and try to divide 
it with 81. The 162 kHz signal you pick off the air is an analog signal, 
and it will suffer from all kinds of unwanted noise, dips and multipath 
phenomena. I assume you plan to condition the signal so that you can 
feed it to a digital divider. However, this is an invitation to cycle 
slips and jumps.

An off-air frequency reference receiver like the Halcyon OFS-1 fed an 
amplified and filtered 162 kHz signal directly to a divider, and the 
resulting performance was awful. Take a look at 
https://dabbledoo.weebly.com/halcyon-ofs-1.html

If you live very close to the transmitter site, it may work to condition 
and then divide the 162 kHz signal, but if not, you will not be happy.

Best regards
Ole

Den 21-06-2020 kl. 09:30 skrev Gilles Clement:
> Hi,
> Comparing a reference signal at 162kHz with local 10MHz ocxo. Expected Adev 10E-11 at 10sec.
> 162kHz / 81 = 2kHz = 10MHz / 5000
> GC
>
>> Le 21 juin 2020 à 05:49, Bob kb8tq <kb8tq at n1k.org> a écrit :
>>
>> Hi
>>
>> *Any* divide approach followed by a flip flop clocked by the input clock will meet
>> that same basic requirement. While it *sounds* like it would improve things, it
>> very much depends on the details.
>>
>> What are you trying to do? What is the input frequency? What is the phase noise
>> requirement?
>>
>> Bob
>>
>>> On Jun 20, 2020, at 2:22 PM, Gilles Clement <clemgill at gmail.com> wrote:
>>>
>>> Hi Robert,
>>> You are right, its the lambda divider that was discussed. Need to better understand this approach....
>>> 74HC40103 could also do the 81 Pi-divide easily,  but I tend to prefer the PICDIV concept where the controller is clocked by the signal to divide (So limited or no noise is  added). AVR family could do it, as most of the instructions take only one clock.
>>> Gilles.
>>>
>>>
>>>>> Le 20 juin 2020 à 19:48, Robert LaJeunesse <lajeunesse at mail.com> a écrit :
>>>> Gilles, if I read the Calosso-Rubiola paper correctly a Pi divider is pretty much your standard square-wave producing digital divider, such as a 74163 (for even divides). There's odd-value (3,5,7) Pi dividers shown at https://www.theremin.us/Circuit_Library/symmetrical_digital_dividers.html. What the Calosso-Rubiola paper promotes is the Lambda divider, which is depicted in figure 2 of the paper.
>>>>
>>>> Bob L.
>>>>
>>>>> Sent: Friday, June 19, 2020 at 10:27 AM
>>>>> From: "Gilles Clement" <clemgill at gmail.com>
>>>>> To: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
>>>>> Cc: "Discussion of precise time and frequency measurement" <time-nuts at lists.febo.com>
>>>>> Subject: Re: [time-nuts] Frequency division by 81
>>>>>
>>>>> Hi,
>>>>> Could you point me to a practical design example of a Pi divider ?
>>>>>
>>>>>
>>>>> Envoyé de mon iPad
>>>>>
>>>>>>> Le 19 juin 2020 à 08:56, Poul-Henning Kamp <phk at phk.freebsd.dk> a écrit :
>>>>>> --------
>>>>>>
>>>>>>> I need to divide the output of an OCXO by a factor D=81 for testing purposes. So with minimum added phase noise.
>>>>>> Two stages of divide by 9 PI-dividers ?
>>>>>>
>>>>>> http://rubiola.org/pdf-articles/conference/2013-ifcs-Frequency-dividers.pdf
>>>>>>
>>>>>> -- 
>>>>>> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>>>>>> phk at FreeBSD.ORG         | TCP/IP since RFC 956
>>>>>> FreeBSD committer       | BSD since 4.3-tahoe
>>>>>> Never attribute to malice what can adequately be explained by incompetence.
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