Build your own DIY RTK Guidance

I use the following setup for my AgOpenGPS autosteer system with the free Iowa CORS correction service. The accuracy here in central Iowa seems to be in the 1 - 2 cm range! The correction takes place outside the autosteer system so the autosteer system is setup as a generic WAAS type antenna (but the GPS shows as RTK Fix or Float accuracy). See documentation under pictures. I no longer have time to build these for farmers but will help you get started.

OutFARMING dome

DIY 3D printed dome

Under the cover

With the antenna removed

With the antenna disk removed

Base / Rover System

For NTRIP correction you will need to supply a cell phone and install an app for the correction service. I use the free Lefebure NTRIP app on an Android phone. I'm guessing you might be able to use an IPhone as well.

On Sparkfun.com, go to Home/Tutorials/GPS-RTK2 Hookup Guide and find the "Connecting the ZED-F9P to a Correction Source.

You will want to use the free U-Blox U-Center software to configue the F9P to only output NMEA GGA and VTG sentences to the serial port.

NTRIP Parts:

Sparkfun GPS-RTK2-SMA Breakout - ZED-F9P (Qwiic) $275
Sparkfun GPS Antenna Ground Plate $7
The Sparkfun Bluetooth Mate Silver has been retired and Sparkfun has no replacement. I modified an HC-06 from Amazon to work.
Sparkfun GPS/GNSS Magnetic Mount Antenna SMA - 3m $13
OR the much better antenna: Sparkfun GPS-15192 - $68
Sparkfun Female Headers $1.50
My Plastice dome with magnetic mount: $50 or contact me for the gcode file.
Serial to RS232 conversion kit for AgLeader type use: $75

You will need to buy a special data cable to go from the antenna to the cell phone (find on Amazon). The antenna end needs to be a USB type C male connector and the other end needs to be a male connector matching your phone's charging/data port. I use a USB C male to USB C data exchange cable with a USB C to USB micro converter.

DIY Base/Rover Parts:

In 2017 I used an older U-Blox C94-M8P-2 kit with UHF radio communications: $399. See https://www.digikey.com/en/products/detail/u-blox/C94-M8P-2/6150728. The kit contains 2 identical boards. One is used for the base and the other for the router. I would like to find a way to do it with the newer ZEO-F9P chips but the C099-F8P kit only uses bluetooth and WIFI. The WIFI won't communicate far enough for farm use. Good way might be to use Sparkfun ZEO-F9P boards and XBee 3 Pro units for radio communications.
2 Enclosure boxes @ $24. See https://www.digikey.com/en/products/detail/bud-industries/PN-1334-C/429006. I used one of these and a cheap waterproof camera case? from Menard's hunting supplies.
LM7808 chip for power regulation and prototyping board
TTL to RS232 converter if using with AgLeader type monitor: $16 https://www.sparkfun.com/products/449
12V garden tractor battery for base. Tripod. Various wires and connectors. Contact me if interested.

A good option is to look into the Ardusimple RTK system.