[time-nuts] Brooks Shera

EWKehren at aol.com EWKehren at aol.com
Mon Mar 25 07:53:40 EDT 2013

Bruce, would you mind being more specific and offer a solution.
Thanks   Bert Kehren
In a message dated 3/25/2013 7:09:41 A.M. Eastern Daylight Time,  
bruce.griffiths at xtra.co.nz writes:

The lack  of synchronisers when crossing clock domains is a design flaw 
that should  be corrected.


EWKehren at aol.com wrote:
> Brooks GPSDO  may be 15 years old but is still perfect for today's
> applications. If  you look at tvb's Tbolt plot or Ulrich's plots with and 
>  sawtooth correction for a day or two the limit is GPS. The basic unit 
has  a
> resolution of 1.73 E-13 in mode 7. Brooks uses a 40 bit filter. I  have
> increased  resolution using 100 MHz in stead of 24 and  increasing filter 
time from
> 30 to 60  and 120 seconds. 240 is  also an option, I would only recommend
> any thing above  30  seconds if you use a Rb. The only thing wrong is that
> chips that  where  available 15 years ago are now hard to find. My answer 
is a  $
> 1 gate array and  if some one will step up to the plate and  modify the
> available ASM code to  generate the RS232 code to  control a FE 5680A I 
will make
> a G/A design and a  board design  available. While at it also look at 
> it in a 18 pin PIC.  If  interested contact me off list.
> With hundreds of 5680's out  there many will appreciate a low cost simple
> solution. Working with  the presently available ASM code now out there it 
> be  a very  small effort needed to transfer it to the latest version 
> when  it  becomes available. It will take some one willing and able to  
> up at the  point where the filter output drives the DAC and  develops code
> that reads the  info from the 5680 and generates  the correction code. 
The 5680
> does not control  a DAC but the DDS  in the 6.8 GHz loop.
> As to the input circuit, having looked at many  alternatives I still thing
> it is the best for a 1 pps input from GPS  and its limitations. Hope to 
> some  data available of 1.402.1  driving a Morion in the next couple of 
> I also have a couple of  A&A boards with all original chips and some of  
> 100 MHz  boards with components. Please contact me off list if   
> Bert Kehren  Miami
> In a message dated  3/25/2013 2:30:36 A.M. Eastern Daylight Time,
> attila at kinali.ch  writes:
> On Mon,  25 Mar 2013 00:43:02 -0400
>  "Daniel Schultz"<n8fgv at usa.net>   wrote:
>> Another great ham passes on, I'm sorry I never had a  chance  to meet 
> Definitly a  sad day....
>> Is the GPS  controller  that Brooks published still useful today, or  has
> it been
>> superseded by  something newer?
> That highly depends on what you want and what you   need.
> Shera's design is definitly one of the simplest GPSDOs  out  there.
> And with that it defines what the lowest complexity  to get  something
> accurate is. If the performance of this circuit  is enough for  you,
> i wouldn't go for anything else. Of course,  if you need better  
> or want to tinker and see what  can be done with home made  equipment, 
> you should go for  different circuits.
> Attila Kinali

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