I’m Buying A New RTK Receiver. What Should I get?

In light of this weeks webinar, A Closer Look at L5: The Future of High-Precision GNSS, and spurred by an email from a reader about how to sift through all the GPS/GNSS receiver choices, following are my thoughts if you’re looking to purchase an RTK receiver today.

First of all, an email from a reader succinctly sums up the challenge:

I currently utilize static GPS / GLONASS receivers in my day to day operations and I am looking at buying a couple more receivers (an RTK setup). To be honest, I am totally confused as to what technology I should buy.

Specifically, I don’t know whether or not it is worth buying receivers that have L2C and L5 capabilities. It seems that vendors are not very well educated on what these options can do for you, and how many satellites are up and running that provide these signals. It is my understanding that L2C is simply a civilian code that is carried on the L2 frequency, and that it provides an almanac and atmospheric correction information. I don’t even know if receiving L2C will help me as a surveyor, or if it is more designed for autonomous use in navigation. It sounds like L5 will be of great advantage once the constellation has enough SVs that broadcast it.  It also seems like Galileo will be extremely helpful for surveyors, but who knows when that will be available. Basically, I don’t want to spend thousands of extra dollars for “bells and whistles” that are not yet operational from a practical standpoint, and that won’t be in the near future.

He’s right. There are a lot of moving parts these days in the world of GPS/GNSS. Not only are GPS/GNSS receivers steadily improving (better, smaller, faster, cheaper), but the GNSS themselves (GPS, GLONASS, SBAS) are changing too. Making a decision of which “bells and whistles” to pay for and which ones to pass up is not so easy.

Let’s break it down and see if we can clear things up.

It used to be that when looking to purchase a dual frequency GPS receiver, the choice was simple because RTK receivers came in one flavor, L1/L2.

Do I want RTK (real-time centimeter positioning) or am I satisfied with post-processing the GPS data?

Either way you went, it was an straight-forward decision.

Today, that is not the case. If you choose RTK, there are many options available:

-GPS L1 or GPS L1/L2?

-add GLONASS?

-add L2C?

-add L5?

-add Galileo?

The pricing of these options can be substantial. The reader’s letter goes on…

I have a vendor that is pushing an L2C capable receiver on me for more money than a standard dual frequency dual constellation receiver.  The other option is to spend about $13K more and get the L2C, L5, and Galileo ready receiver.

If you look at what the manufacturer’s are offering for GPS/GNSS RTK receivers, it seems there are generally four choices:

1. GPS L1

2. GPS L1/L2

3. GPS L1/L2 + GLONASS

4. GPS L1/L2 + GLONASS + L2C + L5 + Galileo

GPS L1

longer initialization (issue when working around trees)

short baseline length

Really should have the same base/rover receiver (SBAS), not really suited for RTK Network usage.

GPS L1/L2

Legacy, proven technology.

Upside…less expensive, entry level dual frequency RTK

Downside…GPS “brownouts”, susecptible to semi-codeless sunset

GPS L1/L2 + GLONASS

Eliminates the GPS “brownout” problem.

Increased cost, although some manufacturers include it.

Doesn’t support future signals

Suscpetible to semi-codeless sunset.

GPS L1/L2 + GLONASS + L2C + L5 + Galileo

Eliminates the GPS “brownout” problem.

Ready for future signals

downside…future singals aren’t available yet.

Increased cost