It became technically feasible in the mid 1970s, but was rapidly superseded by cellular networks in the early 1980s, so it is rarely found today.
It was invented by engineer J. T. Murasko of UK radiotelephone manufacturer Dymar Electronics.
Narrowband Frequency modulation is used exclusively, so that the capture effect will select the stronger of two transmitters wherever one predominates.
The deliberate offset prevents this at the expense of a "motorboating" effect.
Transmitters use highly stable crystal ovens as their primary oscillator and frequency synthesisers to generate multiple channels from this.