[time-nuts] MT3339 chipset 10ns jitter?

Mon Nov 26 22:15:09 UTC 2012

Azelio,

I dont have a GPSDO and this will be may first attempt
to make one.
I have a pair of working FE5680 with their 10MHz and PPS
outputs, at 10s integration time the counter measures them
at 10MHz+ 15mHz and 10MHz +45mHz. The counter oscillator
is the opt 04E "high stability" OCXO.
So if I understand correctly my option could be the
"Second choice": the FE5680A 10MHz output as ext timebase
for the counter, and measure the PPS under test period.
Using 1s integrqation I will have 1nS resolution, with
one result per 2s.
Using 10s integraqtion time the counter returns 10digits,
showing 100nS resolution. I will collect one reading every
20s, a slow process. Will this setup be enough?

Fabio

Azelio Boriani <azelio.boriani at screen.it> ha scritto:

> You need a reference to test the PPS output from a GPS receiver. That is,
> you need an already running GPSDO so that its stable PPS output can act as
> the reference for your test. Then you need a time interval counter and use
> the GPS under test PPS as start and the reference PPS as stop (or the other
> way, it is irrelevant which is the start and the stop). It helps if the
> GPSDO's PPS can be offset slightly (say, 200nS, 300nS, ...) so that the PPS
> under test doesn't "cross" the reference. Second choice: you can use the
> counter period measurement, feeding the counter with an external stable
> reference. Last (really the last to use): the counter has a very good
> internal OCXO.
>
> On Mon, Nov 26, 2012 at 10:29 PM, Fabio Eboli <fabioeb at quipo.it> wrote:
>
>> Hello Jacques, and the List.
>>
>> Thank you for sharing these docs.
>> Indeed the PPS specs of the MT3339 are confusing.
>> Maybe measurement on a living specimen can help?
>>
>> I have a R-D 1992 counter, and a GPIB interface.
>> When I will have the GPS I will be able to log
>> some data on the PC, although I never tried to use
>> the Racal Counter remotely I will try.
>> Also I hope somebody can suggest the best way to test
>> the PPS from the gps using the Racal 1992, I'm not a
>> time nut, so I could make gross errors.
>> I was thinking simply to measure and log the PPS
>> connected to input A with the counter set to
>> "Period A", and 10s integration time to gain
>> more resolution, all this for some (many?) hours.
>>
>> Fabio.
>>
>> Jacques Tiete <jacques at tiete.org> ha scritto:
>>
>>
>>  Hello TNutters,
>>>
>>> maybe new thread?
>>>
>>> you can have a look at two specsheets of the MT3339 chipset on my FTP-site
>>> 1) http://nixie.ramdac.be/TNutstuff/MT_IT530_Data_Sheet_rev_1_0.pdf
>>>                 on page 8 "PPS output 100 ms high pulse, rising edge +/-1
>>> μs @ full second GPS epoch..." so it states +/-1 μs
>>> 2) http://nixie.ramdac.be/TNutstuff/gtop module application note -a00
>>> _mt3339 series_.pdf
>>>                 on page 32 "The accuracy level of 1PPS for GlobalTop GPS
>>> module is within 100ns (same for majority of MTK GPS modules).
>>>                                         The reference design below can
>>> help improving this accuracy to within 80ns."
>>>                 but on page 14 "1PPS signal is an output pulse signal
>>> used for timing application, its electronic characteristic are  
>>> listed below:
>>>                                                 1PPS signal and its pulse
>>> width with 100ms duration
>>>                                                 Low Voltage level: 0~0.4V
>>>                                                 High Voltage level:
>>> 2.8~3.1V
>>>                                                 Duration: 100ms (Firmware
>>> customization for duration is available)
>>>                                                 Period: 1s Accuracy
>>> (jitter):10ns"
>>>
>>> So what shall we believe?
>>> The rest of the PDF's make a good read.
>>>
>>> 73's
>>>
>>> Jacques
>>>
>>>
>>>
>>>
>>> Message: 4
>>> Date: Fri, 23 Nov 2012 16:44:27 +0100
>>> From: Jacques Tiete <jacques at tiete.org>
>>> To: "time-nuts at febo.com" <time-nuts at febo.com>
>>> Subject: Re: [time-nuts] time-nuts Digest, Vol 100, Issue 95
>>> Message-ID: <7C466C42-C05A-46E2-B3C4-793672874AC8 at tiete.org>
>>> Content-Type: text/plain;       charset=us-ascii
>>>
>>> About:
>>> {
>>> Date: Thu, 22 Nov 2012 22:26:24 +0100
>>> From: Fabio Eboli <FabioEb at quipo.it>
>>> To: time-nuts at febo.com
>>> Subject: [time-nuts] MT3339 chipset in Globaltop's FGPMMOPA6H
>>> Message-ID: <20121122222624.71854hb9oslingcg at webmail.micso.net>
>>> Content-Type: text/plain; charset=ISO-8859-1; DelSp="Yes";
>>>   format="flowed"
>>>
>>> Hello, while asking info about the FE5682,
>>> I realized that for another project
>>> (model plane data logging) I will buy
>>> some cheap gps modules built around an
>>> MT3339 chipset.
>>> In my mind somewhere I stored the fact
>>> that in the datasheet of these module
>>> is mentioned the pps output, so I checked
>>> and the manufacturer is claiming that it
>>> has "High accuracy 1-PPS timing support
>>> for Timing Applications (10ns jitter)"
>>>
>>> This is the module I'm talking about:
>>> http://www.mirifica.it/store/gps/342-globaltop-fgpmmopa6h-pa6h.html
>>>
>>> http://www.alcom.be/binarydata.aspx?type=doc/GTop-FGPMMOPA6H-Datasheet-V0A.pdf
>>>
>>> Has anybody used this chipset or similar for GPSDO?
>>> I have no experience with discipled oscillators
>>> but if there is any hope that the pps out
>>> of these modules is good for the task maybe
>>> it's time for me to start reading more about
>>> the subject.
>>> The final goal will be to check the timing
>>> of the Rb I have around.
>>>
>>> Thanks,
>>> Fabio.
>>> }
>>>
>>> Hello TNutters,
>>>
>>> I did some test with this module from Adafruit (
>>> http://www.adafruit.com/products/746) and it seems not a bad unit.
>>> Tested it together
>>> with my TBolt and the PPS seems quite stable most of the time, I did not
>>> do any logging and math on the result,
>>> just letting the TBolt trigger the scope and apart from the cable offset
>>> I guess 80% of the time the module was
>>> within 10 to 15 ns.
>>> However the specs are not very clear and it is a typical chip for mobile
>>> use in eg. carnav stuff. I also saw some
>>> other specs where the jitter was specified as 100ns. and even one with a
>>> 1 microsec. so I'm a little confused.
>>> As soon as I have some time I plan to connect this module to a BeagleBone
>>> and do some testing for an NTP server
>>> I think the Beagle is better for this than the RaspBerry because of the
>>> "real" ethernet port.
>>>
>>> Greetz,
>>>
>>> Jacques Tiete
>>> 0499 99 83 78
>>> jacques at tiete.org
>>>
>>> Op 23-nov.-2012 om 00:19 heeft time-nuts-request at febo.com het volgende
>>> geschreven
>>>
>>>
>>>
>>
>>
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