I attempted to read the US Patent for the Equinox but you need an electronics and law degree to understand it. This excerpt seems to describe the Equinox being multi frequency in the patent. There is a ton of information in the patent which is interesting to read but hard to figure out what it all means:
DETAILED DESCRIPTION OF THE INVENTION
A multiple frequency digital metal detector of the invention is a metal detector transmitting and receiving one or more signals of different frequencies generated and processed using digital techniques. In one embodiment, the metal detector generates two or more frequencies sufficiently different of each other so that effective ground rejection and target discrimination/identification become possible (multiple frequency metal detector). This is based on the fact that the response of different metallic targets and that of ground change in a different manner with the frequency of the interrogating magnetic field. However, in another embodiment, the metal detector could generate only one signal with a certain frequency (single frequency metal detector). This would correspond to either a metal detector with minimal cost or to a metal detector optimised for maximum sensitivity at that frequency. In the following, unless stated otherwise, the multiple frequency metal detector is described and the single frequency metal detector is considered as a particular case, when the number of transmitted frequencies is one.