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@LeapSecond.com writes: ----- Original Message ----- From: "Chris Albertson" <albertson.chris@gmail.com> To: "Discussion of precise time and frequency measurement" <time-nuts@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@telenet.be> > wrote: > >> Count me in for an assembled and tested board. Great project. >> Jan >> >> >> >> >> ----- Original Message ----- >> From: <EWKehren@aol.com> >> To: <time-nuts@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@aol.com_ (mailto:EWKehren@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 >> >> >> >> >> >> >> >> >> >> ---------------------------------------------------------------------------- >> ---- >> >> >> > _______________________________________________ >> > time-nuts mailing list -- time-nuts@febo.com >> > To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> > and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > > > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

> 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. Can you clarify the "two orders of magnitude" claim? That's hard for me to believe, I think, without seeing the ADEV plots or actual lab report. I mean, even a cheap XO or TCXO or OCXO can be disciplined against GPS and achieve superb results. Temperature (or rather, temperature rate of change) has little effect short-term. Temperature also has little to zero effect long-term. So it's only in the, what, tau 100 to 1000 or maybe 10000 second range that temperature even matters. As long as the LO is locked to GPS; I assume you're not talking about holdover. Obviously you'd want a slightly shorter loop time constant for a non-temperature-controlled Rb than a fancy temperature-controlled Rb. But does this really make a one or two *orders of magnitude* difference? /tvb

Hi If: 1) You are after better than 1.0 x 10^-13 accuracy 2) You are getting 1 to 9x10^-9 at one second ADEV out of your GPS 3) You have a telecom Rb with 1 to 5x10^-10 temp coef over a 70C delta 4) Your Rb self heats 20 to 30C in still air Here’s some math: You will need at least 10,000 seconds to get a single frequency estimate and likely 100,000 seconds. You are likely to go through temp cycles in a room at a 30 to 90 minute rate. (1800 to 3600 sec). Your room temp swings are *way* outside your likely loop. The Rb will have to deal with them by it’s self. —— Your Rb is “sort of” compensated in the temcom units. It’s more like a TCXO than an OCXO. 1x10^-10 over 50C would give you 2x10^-12 per degree C. That may be better or worse than the sample you have. The “worse” really comes in when you have one that’s a parabola or third order temp curve. At least around here a room swing of 2 to 4 C is pretty normal with the heat or air-conditioning turned on. That gets you into the 4 to 8x10^-12 swing range. In a typical garage you are at 10C and 2x10^-11. If you want that to be *below* your 1x10^-13 goal, you have to knock it down by about 100X. —— Is the goal rational? Well this is Time Nuts …. It is roughly the sort of goal Bert has said they are after. Most of the lightweight Rb’s have a major ADEV hump when the temperature compensation cuts in. Without *good* temperature stabilization, you will not disable this correction. There’s no real way to know what the ADEV is without this hunting until you do it. Because of the self heating (and gradients), it’s not a real easy thing to do. If you are using an ensemble of parts to get the ADEV, temperature likely will correlate between them. You will not get the “group vote” to suppress it the way you some other sources of ADEV. —— Yes, I’m sure Bert can cross the T’s and dot the i’s better than I can, but that’s a pretty good outline of the problem. Bob On Jun 24, 2014, at 4:34 PM, Tom Van Baak <tvb@LeapSecond.com> wrote: >> 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. > > Can you clarify the "two orders of magnitude" claim? That's hard for me to believe, I think, without seeing the ADEV plots or actual lab report. > > I mean, even a cheap XO or TCXO or OCXO can be disciplined against GPS and achieve superb results. Temperature (or rather, temperature rate of change) has little effect short-term. Temperature also has little to zero effect long-term. So it's only in the, what, tau 100 to 1000 or maybe 10000 second range that temperature even matters. As long as the LO is locked to GPS; I assume you're not talking about holdover. > > Obviously you'd want a slightly shorter loop time constant for a non-temperature-controlled Rb than a fancy temperature-controlled Rb. But does this really make a one or two *orders of magnitude* difference? > > /tvb > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.