Today, the standard for RC transmission has become the 2.4Ghz band wich is the same frequency range as the Wifi transmissions.
The main advantage of the 2.4Ghz radios is that multiple users can fly simultaneously based on an automatic selection of an available frequency by the pilot radio. In the past RC pilots had to select one available frequency and tune their radio using an interchangeable quartz to work on that available frequency.
The drawback of 2.4Ghz, like wifi is a relatively limited range (from 400m to 1.5 km depending on the brands) and a poor penetration through any kind of strucures like buildings and even trees or the human body. This is important to know for fpv uses as a pilot may want to circle around a building or even to have the aircraft enter in a building such as in this excellent Detroit video from Trech5000 below:
To achieve this type of fligh the long range systems (LRS) is necessary. Instead of 2.4Ghz, the LRS use the 433mhz band. This frequency has a very high penetration in objects such as buildings. For the flight below in which I fly under a porch and turn around a 10 siecles old abbey, I have used the Thomas Scherrer's Long Range System (TSLRS):
It is important to say that 433 mhz may not be legal in all counties or requires a special license.
Today my systems are:
Futaba T8FG + Robbe Telemetry Box (2.4Ghz)
Spektrum DX7 + Thomas Scherrer Long Range System (433 mhz)
The DX7 required a mod to work with TSLRS that is described here in Fpvmanuals