We recently tested the latest lightweight( < 50g ) GEM1305 RTK receiver with antenna. This RTK chip is based on Allystar’s latest chip but has customized protocols to better support Ardupilot. It supports a 5Hz output rate and has 2 UART outputs. In our testing, we only needed a 6P data cable to fully utilize the RTK function.
Its price is below $50.
During the test, we used Mission Planner for Android version and connected directly to the radio via an OTG cable.
For the base station, we also used a modified model that only required simple configuration to send RTCM to the drone end through ground control software.
If you want better and more stable signal, you can also use a ground plane to enhance it, like this.
The signal can be boosted by about 2-4db.
In Ardupilot configuration, you only need to select GPS1_type as NMEA.
This is a detailed introduction page.
https://ardupilot.org/copter/docs/common-datagnss-gem1305-rtk.html