During the late 40s, while police communications were limited to 1 way traffic on the 1680kHz system, it was obvious that this was not satisfactory, and experiments were made with two way systems.

A prototype transmitter unit was built by a company called Industrial Electronics, which provided a "talk back" facility, similar to the systems in use by the Los Angeles Police. This equipment would allow officers to reply to transmissions from the 1680kHz transmitter, using a VHF transmitter operating at around 80MHz, however this system was not adopted for operational use.

At around the same time the New Zealand Post Office conducted tests in Christchurch with two way VHF equipment, using ex-military aircraft equipment mounted in the boot of a car. The tests were conducted on a frequency around 93MHz and the mobile equipment was used to communicate with a base station located on the Port Hills, a nearby high point. These experiments were successful, and paved the way for the introduction of a police 2 way VHF service.