[time-nuts] Brooks Shera

EWKehren at aol.com EWKehren at aol.com
Mon Mar 25 06:52:56 EDT 2013

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 without  
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 putting 
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 will 
be  a very small effort needed to transfer it to the latest version 1.402.1 
when it  becomes available. It will take some one willing and able to pick 
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 have 
some  data available of 1.402.1 driving a Morion in the next couple of days.
I also have a couple of A&A boards with all original chips and some of  my 
100 MHz boards with components. Please contact me off list if  interested.
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 him.

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 superseded by  something newer?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  performance
or want to tinker and see what can be done with home made  equipment, then
you should go for different circuits.

Attila Kinali

The people on 4chan  are like brilliant psychologists
who also happen to be insane and  gross.
--  unknown
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