[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
> superseded by something newer?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.
The people on 4chan are like brilliant psychologists
who also happen to be insane and gross.
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