[time-nuts] Re: Brooks Shera GPSDO

[glen english LIST]

Hi Arnold

The 24M and 6M must be synchronous to avoid adding an edge uncertainty .

But that isnt too hard to manage, just start with a  5V  24 MHz 
oscillator (anything, or say a 74AC14 and a 24 MHz crystal)Â  and a fast 
, say 74AC74 dual D type flip flop for 6 MHz (AC to keep the div 4 prop 
delay down and more consistent with temp).

The speed this will run at is very much dependent on the logic family . 
this board is built with 74HC and an accompanied old slow PIC.  You'd 
need to change the logic and the processor software to use other higher 
freqs.

There was nothing really special about this design except it was a 
simple technique done well and used some novel ideas to permit 
relatively low performance computing hardwaree to measure with a high 
precision.

regards,

Glen.

On 21/02/2022 3:50 am, Arnold Tibus wrote:
> Very interesting to read about this good old design!
>
> I have still a board for the Brooks Shera GPSDO and I would like to
> complete it, but I cannot find the described 24 MHz/ 6 MHz Oscillator.
> So I have some questions to it.
>
> Is it neccessary that these frequencies are exact and running 
> synchronous?
> Are there special tcxo available which would fit?
> Could I run this board as well with other (e.g. higher) frequencies and
> of independent oscillators?
> Are there improvements in meantime?
>
> regards,
>
> Arnold, DK2WT
>
>
> Am 20.02.2022 um 03:11 schrieb glen english LIST:
>> Larry, Take a look at Brooks Shera's article in QST. you might know 
>> of it.
>>
>> In my opinion, this has been the 'best ever' description of rolling your
>> own.
>>
>> The July, 1998 issueBrooks Shera, W5OJM, titled, "A GPS-Based Frequency
>> Standard. <https://www.qsl.net/n9zia/wireless/QST_GPS.pdf>"
>>
>> https://www.qsl.net/n9zia/wireless/QST_GPS.pdf
>>
>> I build several of these and they made "good" GPSDOs
>>
>> much has been written about this, and emulating it for other hardware.
>>
>> https://k6jca.blogspot.com/2018/12/simulating-brooks-shera-w5ojm-gpsdo.html 
>>
>>
>> https://github.com/k6jca/Brooks-Shera-GPSDO
>>
>> u can still buy the original PCB PCB
>>
>> http://www.a-aengineering.com/gps.htm
>>
>>
>> On 20/02/2022 10:59 am, Larry Gadallah wrote:
>>> After poring over the several valuable references people have posted
>>> here, it seems that even the common commercial GPSDOs have
>>> implementation problems, so it seems like there's no (financially
>>> viable) off the shelf solution.
>>>
>>> It would indeed be convenient to have a kit option, but I'd image the
>>> potential marked for a GPSDO kit is vanishingly small.
>>>
>>> FWIW, I started with a VE2ZAZ board and an Isotemp OCXO and a Motorola
>>> receiver of questionable provenance. Since then I've gathered an HP
>>> 10811D and I have an HP E1938A coming (I think), so I have only so far
>>> gathered some essential components that I hope are competent.
>>>
>>> On Sat, 19 Feb 2022 at 07:13, Bob kb8tq <kb8tq at n1k.org> wrote:
>>>> Hi
>>>>
>>>> Building a kit is very different than a from scratch design. A
>>>> Heathkit (to extend the years ago ham radio analogy) radio
>>>> was an option when you shopped for your Drake. Building it
>>>> would give you some experience.
>>>>
>>>> The Heathkit *design* was done for you and all the complicated
>>>> higher level stuff was worked out / tested out / reworked / retested
>>>> by somebody else. As long as you put it together correctly, it
>>>> worked and was a good radio.
>>>>
>>>> These days there aren’t a lot of folks selling kit GPSDO’s. Even
>>>> the kit radio business isn’t what it once was. “I’m going to do
>>>> a GPSDO” these days generally means a scratch design.
>>>>
>>>> Bob
>>>>
>>>>> On Feb 19, 2022, at 2:41 AM, Bill Beam <wbeam at gci.net> wrote:
>>>>>
>>>>> But there is a magazine article....
>>>>> <https://www.qsl.net/n9zia/wireless/QST_GPS.pdf>
>>>>> By Brooks Shera, W5OJM.  QST July, 1998.
>>>>>
>>>>> Following this article I built my unit in 1998 using his PCB and a
>>>>> Motorola UT+.
>>>>> It has been running almost continuously since then - almost 25 years.
>>>>> It has been thru several HP 10811 and 10844 oscillators during that
>>>>> time.
>>>>>
>>>>> Even though Brooks is SK his GPSDO is still running.
>>>>>
>>>>> Regards.
>>>>> Bill, NL7F
>>
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-- 
Glen English
RF Communications and Electronics Engineer

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