# NMEA messages necessary for ntp server

**URL:** <https://community.ntppool.org/t/nmea-messages-necessary-for-ntp-server/1792>\
**Category:** Server operators\
**Created:** [September 23, 2020, 11:05am UTC](https://community.ntppool.org/t/nmea-messages-necessary-for-ntp-server/1792 "2020-09-23T11:05:27Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![NoriAbe](https://avatars.discourse-cdn.com/v4/letter/n/48db29/32.png) [@NoriAbe](https://community.ntppool.org/u/NoriAbe)\
**Post date:** [September 23, 2020, 11:05am UTC](https://community.ntppool.org/t/nmea-messages-necessary-for-ntp-server/1792/1 "2020-09-23T11:05:27Z")

</div>

Hi, my name is Nori Abe from Japan. I’m creating a ntp server on RasPi 4B.  
The ntp server receives GPS and PPS signal from GNSS sensor, Spatial Dual  
made by ADVANCED NAVIGATION, and corrects its time.

Once booting up my RasPi, ntpq -p status shows

```
remote refid st t when poll reach delay offset jitter
============================================================================
*SHM(0) .GPS. 14 l 1 16 377 0.000 7.196 1.457
oPPS(0) .PPS. 0 l 19 64 377 0.000 -2.369 10.883
+ntp-a3.nict.go. .NICT. 1 u 15 64 177 13.840 41.227 21.948

```

It looks like OK.

But after a while, it shows

```
   remote refid st t when poll reach delay offset jitter
==============================================================================
xSHM(0) .GPS. 14 l 8 16 377 0.000 9.534 0.708
xPPS(0) .PPS. 0 l 26 64 377 0.000 0.085 5.913
xntp-a3.nict.go. .NICT. 1 u 11 64 377 13.936 58.650 12.450

```

It’s not good I think.

I know my GNSS sensor does NOT send GPGSV, which tells satellites status.  
I’m wondering such missing NMEA message affect the bad status.

Could you teach me what NMEA messages does ntp server needs for correct  
behavior? If you have any good documents, I’d be appreciated.

Thank you,