As good as possible. GNSS in general requires
very good sky view for reliable and repeatable results.
Yep, there a many designs out there for ground use.
Only thing I will say is get a design that uses a patch style antenna (like harxon gps500 or sparkfun top106) and not a helical/helix design.
The RFD900 will not communicate with Emlid’s M2 LoRa radio. You would need to connect another RFD or a 3DR SIK radio to the M2 in order to communicate. I haven’t found another LoRa radio that will communicate with Emlids.
You either need to use two Emlid radios or two matching 3rd party radios
The rfd modem works really well. I was using a pair for my RS2 and M2 for bathymetry work. Reason was my Lora radio for the M2 was delayed for a month as shipping came to a halt with all the flooding in BC. RFD modems theoretically can transmit to 40km. I presume the would be a yagi or patch antennas. I’ve gotten over 10km with no issue. Both the rfd and Lora won’t do well in canopy. Either way, watch your fresnel zone. Aka, go high lol!
I haven’t done a true range test with my setup but there are affordable ways to do it.
I actually bought a pair of RGD900+ (1W output)and a pair of 3DR SIK radios (1/2W output, they range in price from $40-100 depending on brand). The 3DR pair with the RFD when it was on firmware 1.9 I don’t need the 1W radio on the rover just the base.
I found the Multipoint software for the RFD on their Firmware page and found a corresponding for the 3DR radios, Now I can have multiple rovers connected to one RFD.
As stated above, 900 mhz and vegetation do not go together well.