[time-nuts] FE5680 GPS Disciplined Controller Update
EWKehren at aol.com
EWKehren at aol.com
Tue Jun 24 19:50:30 UTC 2014
The response has been very positive such that a $ 45 kit is doable. Working
on getting at least two beta tests lined up.
However it is disappointing that no one has stepped up to tackle the
temperature problem. how many have looked at the temperature attachment and
clicked on the N5TNL link. Let me make it clear that yes the GPSDO will work but
there will be one or two orders of magnitude degradation without active
fan temperature control unless the internal temperature compensation is
disabled.
I like to float an other idea I did attach a picture of the auxiliary board
which we also use on other projects. That board along with inductors and
two mini circuit transformers could be added to the kit for an extra $
8.00. Other parts are readily available. Going forward it would make sense to
have a temperature control board and a clean up loop board. We have them but
they are express PCB. if members would be willing to do a Gerber version I
will gladly work with them off list and than they could be added for an
extra $ 4.00 to the kit. We do not have the time. Total kit would be $ 57.00
maybe $ 55.00 including four 5 X 5 cm. boards.
Let me know what you think.
Bert Kehren
In a message dated 6/19/2014 2:56:52 P.M. Eastern Daylight Time,
tvb at LeapSecond.com writes:
----- 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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