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 <[email protected]> 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 <[email protected]> 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 <[email protected]> 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 <[email protected]>
To: "[email protected]" <[email protected]>
Subject: Re: [time-nuts] time-nuts Digest, Vol 100, Issue 95
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
About:
{
Date: Thu, 22 Nov 2012 22:26:24 +0100
From: Fabio Eboli <[email protected]>
To: [email protected]
Subject: [time-nuts] MT3339 chipset in Globaltop's FGPMMOPA6H
Message-ID: <[email protected]>
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
[email protected]
Op 23-nov.-2012 om 00:19 heeft [email protected] het volgende
geschreven
----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
