I’m gonna install an NTP server to get the signal from a GPS antenna. The gain of the GPS antenna is 33dB, and I’m using coaxial cable LMR400 from the antenna to the NTP server. The length of the Cable is 20 meters, and I don’t have any splitter. I need to make sure the level of the signal to the NTP server isn’t too high or too low. I’m just looking for a method to measure the signal level before connecting the cable to the NTP server. The antenna needs 5VDC to work:
can I use a Bias-T like shown in the attached block diagram to feed the Antenna?
An NTP server won’t be able to do anything with a GPS antenna, you need a GPS receiver connected to the GPS antenna. The GPS receiver then sends data to your NTP server and the software on the server extracts time from that data.
Signl level is important to the receiver but any antenna with a clear view of the sky will have plenty of signal.
Don’t waste your time with a spectrum analyzer, it’s not going to give you any useful data and a GPS receiver will tell you signal strength anyway.
Each satellite is a different distance away, the receiver should be able to give you a CNO / dBHz measurement for each. Reports via NMEA GSV sentence, or UBX-NAV-SAT/SVINFO
The newer uBlox receivers, M9, M10 and F9, F10 should be able to provide a Spectrum via UBX-MON-SPAN in uCenter Classic.
20 meters of LMR400 with a 33 dB should work just fine. Might expect CNO in mid to upper 40’s
What you really need to distance to achieve is placing the antenna in an ideal location, with the broadest view of the sky, horizon to horizon.
YellowDog:
An NTP server won’t be able to do anything with a GPS antenna, you need a GPS receiver connected to the GPS antenna.
Great answer - and with respect to measuring the signal → spectrum analyzer is the only way (scope won’t do it) but it is not trivial; and why do it since the GPS receiver does indeed provide a signal quality level number and it could also simply be calculated if really needed.
