Professionals have used dual-frequency positioning receivers (SatNavs) for many years. But they are expensive. Recently, much lower-cost dual-frequency receivers have become available, such as the u-blox ZED-F9P. This receiver can operate as a regular positioning receiver, with or without RTK, or as a source of RTK corrections (RTK base station). Dual-frequency operation means that the receiver has more signals to play with, so you get a better position fix. It also means that the receiver can deduce the ionospheric corrections without the need for SBAS (also known as DGPS). The ZED-F9P receives all four constellations of satellites which are currently flying, so it has a large number of signals available. This is also an advantage for RTK, because it means the algorithm can converge in one or two seconds if you are close to the RTK base station or if you are using a Virtual Reference Station (VRS).

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