Hopefully this thread will allow us to share our experiences with different RTK GPS units and allow feedback & ideas from others. It will focus on finding cheaper solutions to allow us to collect accurate Ground Control Points.
I personally use a HiPer SR from Topcon as a Network Rover. It's L1,L2, & Glonass.
My setup is a $8,500 HiPer SR receiver plus a $1500 Data collector. I use my IPhone as a WiFi Hotspot to allow my data collector to receive Base Station Corrections from a NTRIP Caster. This setup is commonly called a "Network Rover" because it's a RTK Rover using Base Station Corrections sent over the internet. In most circumstances I can get centimeter positions "real-time" with a proper workflow.
The Cheapest Turn-Key Solution for centimeter positions that I know of is to purchase the Dual Frequency X90-OPUS Receiver for $1880 and log static data for 30 minutes to 2 Hours. (Longer occupation times are usually not required for UAV mapping precisions). http://x90gps.com/index.htm
You press 1 button to log the Static data which you later upload to the OPUS website (http://www.ngs.noaa.gov/OPUS/index.jsp) and a x,y,z solution is emailed back to you.
You can use this receiver to determine precise base station coordinates for a DIY RTK system, or simply log static data for each of your UAV Ground Control Points.
OPUS Map of Estimated Precision
For the DIY crowd :
What I'm most excited about is the PRECIS L1/L2 GNSS board by Tersus for $800
[EDIT - Updated 02-02-2016]
Manufacturer now sells a complete RTK kit for $1,999
My plan is to build a DIY RTN GPS (Real-Time-Network vs. RTK) with the $800 PRECIS board, $20 Bluetooth module, Android Phone as data collector running a free NTRIP Client, and obviously antenna/battery/etc. The Android Phone will receive free RTK corrections through a free NTRIP Client. Again, this type of setup is commonly called a "Network Rover" because it's a RTK Rover using Base Station Corrections sent over the internet w/ RTCM protocol. This setup should provide the same functionality as my $10,000 GPS & Data Collector and provide real-time centimeter positions.
This unit should function fine with any geodetic antenna such as a Trimble Zephyr that can be found on Ebay for $500. I'm interested in testing the performance with cheaper $50 - $100 active antenna's, but haven't had the opportunity yet.
Real-Time-Network Base Station LIST for each STATE
For example, my coverage MAP for Mississippi shows the location and current status of all the Base Stations in the free MS Network:
I'm discussing w/ the manufacturer of the PRECIS board - the possibility being able to log Raw Static data in RINEX format in the future. The ability to log the RAW observables would allow us to perform a Static Survey and upload to OPUS when Cellular Data is not available for a Network RTK Correction, or if there is no Base station close enough in the free Network for a specific project location to provide a fixed solution.
Another option is to purchase 2 of the PRECIS boards, and have them communicate as Base/Rover with the same $50 3DR telemetry radios we use in our UAV's. Of course, you still need to determine an accurate position for the base station. This can be accomplished by first measuring the base position as a Network Rover, or if no cell coverage is available you would log a static session and upload to OPUS if the RINEX format can be output from the board.
Note: Novatel makes several boards similar to the PRECIS in their OEM 6 Line for around $800 also.
Single Frequency RTK :
$1,000 for a L1 Carrier Phase RTK kit.
Using single frequency RTK (L1 Carrier Phase) has many challenges in the field.
$570 for a L1 Carrier Phase RTK kit, same challenges as above.
$50 RTK Capable L1 GPS Receiver, same challenges as above
NS-HP User Manual
NS-HP Data Sheet
NS-HP Applications Sheet
The NavSpark NS-HP RTK appears to be the RTK cheapest solution, but will also be frustrating in the field. This unit will experience the same hardships as the Piksi & Reach L1 RTK's in regards to maintaining the Carrier Phase Lock. I am planning to experiment with the NavSpark NS-HP since it's much less expensive than the Piksi or Reach.