# Which GPS Raspberry Pi hat for stratum 1 server? **URL:** \ **Category:** Server operators\ **Created:** [February 10, 2020, 2:40am UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580 "2020-02-10T02:40:02Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![lammert](https://sea2.discourse-cdn.com/flex016/user_avatar/community.ntppool.org/lammert/32/82_2.png) [@lammert](https://community.ntppool.org/u/lammert)\ **Post date:** [February 10, 2020, 2:40am UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580/1 "2020-02-10T02:40:02Z")
My current Stratum 1 server is a Raspberry Pi connected with a Garmin 18x LVC GPS receiver. This is a general-purpose GPS receiver which I previously used with a normal x86 server. The good thing is that it has a long cable, which makes it possible to mount the antenna outside, but I now want to replace it with a genuine GPS hat on the raspberry. Has anyone here experience with good GPS hats? PPS accuracy is important obviously. Are there any GPS hats with an RTC backup clock? The Raspberry isn’t shipped with a clock chip and at startup, it defaults to January 1st, 1970, until the GPS clock has synchronized. It would be nice to start with a plausible time, rather than jump some decades each time the device is restarted. ---
**Author:** ![apuls](https://sea2.discourse-cdn.com/flex016/user_avatar/community.ntppool.org/apuls/32/1467_2.png) [@apuls](https://community.ntppool.org/u/apuls)\ **Post date:** [February 10, 2020, 12:53pm UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580/2 "2020-02-10T12:53:05Z")
I have one GPS Recv. without RTC - didn’t test it yet. It’s a µBlox Neo-6M IIRC. This one have an µBlox M8 with internal RTC [https://store.uputronics.com/index.php?route=product/product&product\_id=81](https://store.uputronics.com/index.php?route=product/product&product_id=81) If you just want to save your current dat / time for bootup, take a look at the Debian package “fake-hwclock”. It saves the current date on shutdown / reboot to a file and setup the clock on startup with it. ---
**Author:** ![alica](https://sea2.discourse-cdn.com/flex016/user_avatar/community.ntppool.org/alica/32/337_2.png) [@alica](https://community.ntppool.org/u/alica)\ **Post date:** [February 10, 2020, 3:59pm UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580/3 "2020-02-10T15:59:32Z")
Another GPS HAT with RTC: > **[Adafruit Ultimate GPS HAT for Raspberry Pi A+/B+/Pi 2/Pi 3](https://www.adafruit.com/product/2324)** > > It's 10PM, do you know where your Raspberry Pi is? If you had this GPS HAT, you would! This new HAT from Adafruit adds our celebrated Ultimate GPS on it, so you can add precision time ... I just bought one along with a Pi 4 kit from element14, but found it interferes with the official case (lid cannot be closed), so have not booted the assembly up yet. ---
**Author:** ![lammert](https://sea2.discourse-cdn.com/flex016/user_avatar/community.ntppool.org/lammert/32/82_2.png) [@lammert](https://community.ntppool.org/u/lammert)\ **Post date:** [February 10, 2020, 6:23pm UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580/4 "2020-02-10T18:23:22Z")
Thanks for the recommendations. Saving the previous time at shutdown unfortunately won’t work. It is mostly to prevent losing time when power is lost. I have now had a few occasions where the power was lost to both the Pi and the router. After startup the PPS signal was the first signal available to synchronize causing the chronyd daemon to fix on January 1st 1970, even though the NMEA GPS time and later the connected external NTP servers said otherwise. The daemon refused resynchronization with a message that the step to the correct time was too large, effectively marking the good servers as bad, and the bad internal software clock + PPS as good. 🥴 My first idea was to switch to a model like the Adafruit with the antenna built-in, but when I checked the specs the sensitivity is -165 dBm whereas my current external antenna has a sensitivity of -185 dBm. So I’ll probably have to go with an external antenna version anyway, because where I plan to mount the device, my current GPS is just capable of fixing on enough satellites. The Adafruit seems in that regard the most promising one as the datasheet mentions a minimum of 7 years RTC function on battery without external power. The Uputronics mentions an optional battery in the data sheet, but a supercap in the product description. Time to do some more research before making the final decision. Thanks for your input so far! ---
**Author:** ![apuls](https://sea2.discourse-cdn.com/flex016/user_avatar/community.ntppool.org/apuls/32/1467_2.png) [@apuls](https://community.ntppool.org/u/apuls)\ **Post date:** [February 10, 2020, 6:36pm UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580/5 "2020-02-10T18:36:11Z")
Or just add an RTC to your Pi. You can get some boards for around 7$ or 5€ (on [amazon.de](http://amazon.de)). They are plug’n’play. ---
**Author:** ![lammert](https://sea2.discourse-cdn.com/flex016/user_avatar/community.ntppool.org/lammert/32/82_2.png) [@lammert](https://community.ntppool.org/u/lammert)\ **Post date:** [February 10, 2020, 8:30pm UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580/6 "2020-02-10T20:30:12Z")
There is no room for an RTC board anymore. I currently already use a serial board on top of the pi to connect the GPS to. ---
**Author:** ![elljay](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@elljay](https://community.ntppool.org/u/elljay)\ **Post date:** [February 11, 2020, 9:05am UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580/7 "2020-02-11T09:05:41Z")
[Chrony’s](https://chrony.tuxfamily.org/faq.html) suggestion is: ### 5.5. What if my computer does not have an RTC or backup battery? In this case you can still use the `-s` option to set the system clock to the last modification time of the drift file, which should correspond to the system time when `chronyd` was previously stopped. Not sure how often chrony updates the driftfile, but I guess it’s more often than just at (clean) shutdown. ---
**Author:** ![lammert](https://sea2.discourse-cdn.com/flex016/user_avatar/community.ntppool.org/lammert/32/82_2.png) [@lammert](https://community.ntppool.org/u/lammert)\ **Post date:** [February 12, 2020, 2:01pm UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580/8 "2020-02-12T14:01:53Z")
Thanks for the hint. I didn’t know this -s option. It looks like my drift file is updated every hour. ---
**Author:** ![magnemann](https://sea2.discourse-cdn.com/flex016/user_avatar/community.ntppool.org/magnemann/32/1318_2.png) [@magnemann](https://community.ntppool.org/u/magnemann)\ **Post date:** [August 20, 2026, 8:50am UTC](https://community.ntppool.org/t/which-gps-raspberry-pi-hat-for-stratum-1-server/1580/9 "2026-08-20T08:50:12Z")
I ordered this, it should be more accurate than adafruit > **[GPS/RTC Expansion Board for Raspberry Pi](https://thepihut.com/products/raspberry-pi-gps-hat)** > > The Uputronics GPS/RTC Expansion Board for Raspberry Pi provides a modern multi GNSS GPS receiver and hardware RTC with no soldering required. It can be connected to all Raspberry Pi boards with the 40-pin (2x20) header. see also this thread > [@Recommendations for GPS-hat for raspberry pi 4](https://community.ntppool.org/t/recommendations-for-gps-hat-for-raspberry-pi-4/4635): > > Hi, I will build a S1 server with a rpi 4, and need a hat with PPS, no soldering. Antenna on roof, clear sky. Located south in Norway. Important is also accuracy (and price). Anyone have experience on certain hats? Thanks a lot grinning_face