SG-2340/MBT-4220 GPS-Lure Stratum-1 NTP clock under pfSense?



  • @stephenw10 Just had an idea: is the external antenna detected automatically, or do the init commands enable it? If it's not automatic, and the integrated patch antenna is being used, inside of what's a metal case with a few vents, in a basement, I'd 100% be not surprised it can't get a satellite lock.

    On the other hand, if the switch-over is automatic, then I am surprised, because I'd expect an external antenna to have a better reception than what my iPhone gets, and that has no issue locking on to the GPS signal, basement and all.

    Wonder where I can find out, if the external antenna is recognized automatically...


  • Netgate Administrator

    Hmm, good question. Can you move it somewhere with better reception for the patch antenna as a test?

    Steve



  • @stephenw10 Not really, because of where internet comes into the house. I could just try to run the box stand-alone for a while to test, both with and without the cover of the case, and with and without the external antenna (if for some reason it should be busted), but I'd have to do that when I don't need access to the internet for a period of time...


  • Netgate Administrator

    Ok, looks like the external antenna is (or should be) used automatically. Does what you're using meet these specs?
    https://docs.netgate.com/platforms/minnowboard/lures/gps-lure/external-antenna-spec.html#recommended-external-antenna-specification

    Steve



  • @johnpoz said in SG-2340/MBT-4220 GPS-Lure Stratum-1 NTP clock under pfSense?:

    Yup you could go that route for sure... Or for like less than a $100 total and a few minutes time you could setup a pi with a hat and run that as stratum 1.. I have one on my home network, that serves to the pool and my local network for like couple of years now.

    Hi @johnpoz - have been following this thread and your post about using a Pi as a Stratum 1 NTP server intrigued me. Did a bit of research, and I think this could be a fun little project. Do you mind sharing a bit more how you went about it? For instance, did you follow a guide like this?

    https://www.ntpsec.org/white-papers/stratum-1-microserver-howto/

    Also, which components did you end up using for the Pi, especially which GPS module (HAT) and did you choose, and did have modify the Pi's case to make room for the GPS module's SMA connector?

    Thanks in advance.


  • Netgate Administrator

    It's no doubt a fun project but could you start a new thread for that in general discussion?

    This is the Netgate hardware section.

    Steve



  • @stephenw10 I used these:

    https://sixfab.com/product/sma-to-u-fl-rf-adapter-cable-150mm/

    and

    https://sixfab.com/product/external-active-gps-antenna-29db-sma-plug/

    which by my reading should fit the spec, but it's well possible I missed something crucial.



  • @stephenw10 said in SG-2340/MBT-4220 GPS-Lure Stratum-1 NTP clock under pfSense?:

    It's no doubt a fun project but could you start a new thread for that in general discussion?

    This is the Netgate hardware section.

    I posted it here, since both the GPS lure and the SG-2340 nee MBT-4220 were sold and bought by Netgate. AFAIK, Netgate is the prime source of the GPS lure.
    So I figured that would be the appropriate place, as I'm trying to get Netgate hardware running with Netgate software.

    But if there's a better spot for this, by all means, move the thread there.


  • Netgate Administrator

    No, you're fine here. 😀

    I meant discussion of a RasPi NTP server which would be neither Netgate or pfSense so more general discussion. Sorry I should have included an @tman222.

    Steve


  • Netgate Administrator

    I don't see any actual specs on that antenna. Was it supplied with anything additional?

    I would also expect it to work though....



  • Sure thing @stephenw10; apologies for going off-topic.

    Here is the new thread:

    https://forum.netgate.com/topic/143727/building-a-stratum-1-ntp-server-using-raspberry-pi



  • @stephenw10 said in SG-2340/MBT-4220 GPS-Lure Stratum-1 NTP clock under pfSense?:

    I don't see any actual specs on that antenna. Was it supplied with anything additional?

    I would also expect it to work though....

    Description lists this:

    *Description
    This GNSS (GPS, Galileo, Glonass) antenna has magnetic radome so it will stick to any steel structure like a roof of a car. It draws between 5-15mA and works in 2.2-5V DC range. You will need a sort of SMA to u.FL adapter cable to use it with u.FL modules/shields.

    50-ohm impedance
    3-meter cable length with standard SMA connector
    Polarization: RHCP
    Radome Material: ABS
    LNA Gain: 29±1 dB
    Noise Figure: 1.5dB
    Gain(Zenith): 3dB
    V.S.W.R: <1.5*



  • I'm thrilled to report, that it seems the GPS receiver finally has a lock, and I seem to get time just fine! :)

    NTP widget.png

    The settings used are:

    GPS Type: MediaTek
    Serial Port: cuau2
    Port speed: 9600 baud
    NMEA Sentences: All
    Fudge Time 1: <empty>
    Fudge Time 2: 0.400
    Stratum: <empty> i.e. 0
    Flags checked: Prefer this clock, Display extended GPS status
    Flags unchecked: all others, in particular the PPS
    Clock ID: <empty> i.e. GPS
    GPS Initialization:

    $PMTK225,0*2B
    $PMTK314,1,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0*28
    $PMTK301,2*2E
    $PMTK320,0*2F
    $PMTK330,0*2E
    $PMTK386,0*23
    $PMTK397,0*23
    $PMTK251,9600*17
    

    Auto correct malformed init commands: checked

    This is what got things working, after a LONG LONG wait. So at least it seems the external antenna is working and up to spec, if anyone else needs the same.

    So, having low expectations, that just made my day :D


  • Netgate Administrator

    Nice. What sort of jitter, offset etc do you see without the PPS signal?

    Steve



  • @stephenw10 said in SG-2340/MBT-4220 GPS-Lure Stratum-1 NTP clock under pfSense?:

    Nice. What sort of jitter, offset etc do you see without the PPS signal?

    Reported jitter is itself jittery: have seen it as low as 6-ish and as high as 235-ish. So it's all over the place.

    So on the low side: fine, on the high side: not ideal.

    I wonder if raising the baud rate and reporting frequency would help. I think the module is capable of 5Hz or even 10Hz up reporting, with the proper settings and baudrate.

    That would require some further tweaking of the init commands.


  • Netgate Administrator

    Mmm, yeah that's not great. With the PPS signal the jitter can be waay below 1ms. I think johnpoz was seeing ~10μs on his RasPi setup. Something must be done! 😀

    Steve



  • The idea to increase the update frequency may be foiled:
    for a higher update frequency (like 5 or 10Hz), it requires a correspondingly higher baud rate.
    The problem is, the firmware of the module specifies what default baud rate the module has, and I think these are programmed with 9600 baud.
    It is possible increase both update rate and baud rate with corresponding commands, the problem is, pfSense doesn't have a pre and post configuration baud rate.
    So if I indicate a higher baud rate in pfSense, then it won't be able to talk to the module to set the baud rate to the higher rate, and if I set 9600, and then tell the GPS module to go faster pfSense is stuck at the lower rate, as there's no "auto" setting.

    So either pfSense would need to have an auto-baud setting, so it could sync up at 9600, send over the new config, and then resync at 38400 or 115200, or one would need an init baud rate, and a post-init baud rate, to which it would switch once the init commands are sent.

    In any case: I can't get pfSync to use a higher rate successfully, because either I can't send the init commands, or pfSync won't sync after.

    That means I'm stuck at the 9600/1Hz situation, unless I'd somehow took the risk of attempting to flash different firmware settings, so the module would communicate at 38400 or 115200 out of the the gate.



  • I know this thread is a bit dated, but a lot of good information here on using GPS with pfSense:

    https://forum.netgate.com/topic/51920/gps-receiver-ntp

    My original intention was just to try to a USB based GPS receiver since it's the cheapest approach, but upon seeing the warning in the documentation and reading that threat, it seems like a waste of time and money. PPS capability is also really important. Some more useful info:

    http://support.ntp.org/bin/view/Support/InexpensiveOemGps


  • Netgate Administrator

    Wow was that 2013. Yikes! 😬


  • Netgate Administrator

    Do you see a solid red LED on the lure when it has satellite lock?

    Steve



  • @stephenw10

    Something was blinking red at some point, just noticed the blinking, since the system is in a case, I’m not sure what.
    Can’t check now, as the unit is now at a remote site.
    If it’s important somehow, I can check it out myself in a couple of months...
    ..,otherwise I’d have to get maintenance staff involved.
    Is there a particular reason you ask?


  • Netgate Administrator

    It isn't important. As far as I can see from the data sheet that's what it should do. Blinks at 0.5Hz without lock then solid once it has a 3D fix. But it can be set in firmware for other behaviour.
    I have one to play with now myself so I'll let you know, if it ever gets a fix that is! TTFF from cold is.... um loooong.
    Of course my antenna is not ideally placed. The chipset itself looks to be capable of TTFF in 45s so....

    Steve



  • Lock on to GPS NEVER happened with the built-in antenna, as the metal case, despite air vents, seems to have pretty much shielded that.
    On the other hand, once the external antenna was connected, it was relatively swift in picking them up.
    So I think it’s either taking the cover off, or using an external antenna, for which the case is fortunately well prepared, with a pre-made hole for the connector.


  • Netgate Administrator

    For reference the 'fix' LED actually goes out entirely when a 3D fix is obtained.
    Might be better to have it stay on solidly instead. I think that default is done to save power in battery driven applications which doesn't apply here. A firmware update might be possible to change that.

    Steve


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