[time-nuts] FE5680 GPS Disciplined Controller

Thu Jun 19 18:49:48 UTC 2014

----- Original Message ----- 
From: "Chris Albertson" <albertson.chris at gmail.com>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Thursday, June 19, 2014 8:31 AM
Subject: Re: [time-nuts] FE5680 GPS Disciplined Controller


> I've been working in the same thing BUT I don't want anyone who builds it
> to need a PCB.  And I want the firmware to load over USB so there is no
> need to ship programmed chips or deal with external programmers.   I think
> I can get the cost below $20.     That said I doubt I'll get 1E-13
> performance out of my Rb.
> 
> My little Arduino based controller has been running now for a couple months
> and keeping a crystal in lock.  The board has a pins left over for a serial
> port that I'll hook up to the Rb.
> 
> The trick to getting the cost down is NOT to do a custom PCB.  Take
> advantage of one of the uP development boards and then for under $5 you get
> the USB interface, D/A and A/D, serial ports, timers and quite a bit of
> logic all  1/3rd the size of a credit card.
> 
> 
> On Thu, Jun 19, 2014 at 12:57 AM, Jan Boutsen <jan.boutsen at telenet.be>
> wrote:
> 
>> Count me in for an assembled and tested board. Great project.
>> Jan
>>
>>
>>
>>
>> ----- Original Message -----
>> From: <EWKehren at aol.com>
>> To: <time-nuts at febo.com>
>> Sent: Wednesday, June 18, 2014 8:49 PM
>> Subject: [time-nuts] FE5680 GPS Disciplined Controller
>>
>>
>>
>> FE5680 GPS Disciplined  Controller
>> With all the FE  5680 rubidium oscillators being used as door stops out
>> there some of us decided  to develop a GPSDO for it. The main question we
>> have:
>> Is there sufficient  interest among time nuts for a discipline controller
>> for the FE5680 to make it  available? Looking at the postings over the last
>> two years I am not so  sure.
>> The  construction and preliminary testing of a Brooks Shera style GPS
>> discipline  controller for the later version (6.81e-13 resolution) of the
>> FE5680
>> has been  completed. We are trying to determine the number of people that
>> would be  interested in obtaining an FE5680 discipline controller (if there
>> is
>> sufficient  interest about $45 a kit shipping included, $75 for an
>> assembled and tested  board, international orders for an additional $5)
>> when
>> it is
>> released.
>> We are also looking for three Beta  testers that would be willing to
>> purchase, assemble, and test our Beta release  controller kit with their
>> own
>> FE5680A and GPS receiver or Tbolt and provide  feedback. Please send an
>> email to
>> _EWKehren at aol.com_ (mailto:EWKehren at aol.com)   Subject Time-Nuts FE 5680A,
>> if you would be interested in being one of the three  Beta testers. A key
>> requirement is the willingness to get to it right away, the  board assembly
>> takes about 30 minutes. Instrumentation to measure results is  also a
>> requirement. We obtained impressive results using a cheap ublox 6M
>> receiver.
>>
>> The  FE5680 GPS discipline controller is a small (2” x 2”) board using 8
>> DIP’s and 1  SOT23-5 package powered by +5v with 0.1” headers for all
>> inputs
>> and outputs. Our  plan is to have the kit supplier solder in the only SMD
>> device on the board. A  GPS receiver 1PPS and 10 MHz sine from the FE5680
>> feed the board with two 9600  baud serial ports sending TTL level tuning
>> commands to the FE5680 and receiving  commands from and sending status data
>> to a
>> PC for data logging and system  control via a simple terminal program.
>> In the chip count are  two opto couplers that allow the use of isolated TTL
>> to USB conversion. These  USB adapters are readily available and furnish
>> the 5 V necessary for the  secondary of the opto circuit. An option is to
>> not
>> use the opto couplers and  send the PIC TTL level RX and TX into a TTL to
>> RS232 adapter. Another option is  to use a TTL to RS232 converter after the
>> opto couplers but then an external 5 V  source would have to be supplied
>> for
>> the opto couplers.
>> As I  mentioned before to get best performance from the FE5680 temperature
>> control is  a must and after much fan and metal work I realized that a Lap
>> Top heat pipe is  the easiest lowest cost solution. Comments appreciated.
>> As
>> an alternative the  temperature correction needs to be disabled.  Otherwise
>> two control loops fight each  other.  If you look close on page 7  of the
>> brochure temperature stability from –10 to +60 C looks good but a closer
>> look
>> and you see 4 E-11 changes over small temperature changes in the -10 to 60
>> C range. Extensive analysis has been done on the FE 5680 A and maybe some
>> one  can tackle that problem. Please look at what N5TNL did. It is attached
>> and click  on his link. The FE 5680A does have a 4 channel MAX 1246 ADC and
>> most likely it  is used to monitor temperature.
>> Also  mentioned before the FE 5680 output is not the cleanest, I did
>> observe it and  some one posted the attached. I apologize but my records do
>> not
>> show who did, so  if you posted the data please come forward. For serious
>> applications where you  are using it as your main reference a clean up like
>> the
>> Morion MV89 or HP 10811  should be considered.
>> This  addition is not required for beta tests but temperature control will
>> help.
>> I am also  enclosing the express PCB layout, be free to use it but it would
>> be more  economical to do a group buy if there is enough interest and some
>> one steps up  to kit.
>> Bert  Kehren
>> To  not exceed the attachment limit the plot will be a separate  posting
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> ----------------------------------------------------------------------------
>> ----
>>
>>
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> 
> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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