NMEA format $GNGGA quality indicator for DP0601

Hi there.

I’d like to ask a few questions about NMEA format using DP0601, after RTK fix.

I checked 3D/DGNSS/Fixed state in u-center, using NTRIP client (national NTRIP caster)
However, when I checked resulting NMEA message, it didn’t seem to say that it is receiving RTK fixed solution.

In NMEA $GNGGA message, there is “quality indicator” which indicates RTK fix status,
and what I saw was “Differential GPS(DGPS) fix” (number “2”), not “RTK fixed solution” (number “4”).

I’m curious that

  1. What should I do to have number “4”, RTK fixed solution state?
    (Which factor could influence this result?)
  2. What is different between Differential GPS fix and RTK fixed solution?
    (The accuracy seemed to be cm-level, but… what is different between these two?)

Thanks for your help in advance.

1:
-Make sure your DP0601 is setting as Rover (accept RTCM /UBX).
-Chose good Basestation data : At least 12 satellite , signle strength > 38dB, provide GPS+GLonass+Beidou…, the distance from Basestation to your Rover should not more than 20km .
-By default, F9P NMEA out on TX1 , and RTCM input on RX2 .
2: Here is short artical prepare DGPS vs RTK: https://www.e-education.psu.edu/geog862/node/1828