All evolution wireless series from the original EW (sometimes called G1) through EW G2, G3 and G4 can all be used together.
But there are some restrictions.
The hardware frequency ranges changed over time with different systems, so if you are mixing and matching across series, just make sure that you have an overlapping frequency range for your transmitter and receiver (because the two devices have to be on the same frequency to work!)
Furthermore, the EW (G1) series did not use a pilot tone function. Therefore, if you want to mix G1 with any of the other systems, you have to disable pilot tone on the G2, G3 or G4 unit that you will use your G1 unit with.
Besides the transmitter and receivers, be careful with antenna splitters or boosters or similar accessories. Because of changing frequency ranges and differing dc power requirements it is not good practice to mix these up across the series.
For example the ASP 1 and ASP 2 should only be used for G1 and G2 series.
The newer ASA 1 or ASA 214 could be used across all series, as long as the power supply is sufficient.
IMPORTANT: EW-D and EW-DX cannot be used with EW G1-G4 as they use different transmission systems - the EW-D(X) is digital, whereas all the others are analogue!
For all other system accessories, please look at the attached file for compatibility.