In 1946 several Auckland and Wellington police cars ( Plymouths), were fitted with modified Gulbransen broadcast band radio receivers set to a frequency of 1680 kHz (just above the AM broadcast band).
The system was one way only and officers had to find a telephone and ring the station if they wished to pass a message back to base.
Police officers who were short of money for the public telephone soon learned that it was possible to get the message through by tapping out the number on the phone hook and speaking into the earpiece when the call was answered.
This "one way" medium frequency service
was in use for about four years until a two way VHF service was introduced
in 1949.
Medium frequency radiotelephone transmitters, owned by the New Zealand Post Office and sited at Musick Point, near Bucklands Beach in Auckland and Tinakori Hill, Wellington were connected by land line to the Central Police Stations. Messages for the patrol cars were broadcast from these transmitters. When the station had a message for a car, an alerting tone would be transmitted, followed either by the message, or by an instruction to either phone the station or return to base.
The AM transmitter used in Auckland was a Collier and Beale model 142 SW-1 manufactured in Wellington 1942. It had a power output of 100 watts and was located at the transmitter site of the Musick Point Memorial Radio station near the present McLeans College in Bucklands Beach. Musick Point was the main Post Office communication station for Auckland. It included the coast radio station ZLD/Auckland Radio which handled marine traffic, and the Aeradio station ZLF for communication with aircraft on trans-Tasman and Pacific routes.
When the police ceased operations on 1680kHz in 1950 the transmitter reverted to it's original function as a backup transmitter for ZLD on the 2MHz marine band, and remained in service until the station was decommissioned in 1993.
It is still there - now owned by the Suburban Amateur Radio Club of Auckland who maintain the old radio station as a clubroom and a monument to the history of radio.
QSL card of the Suburban Amateur Radio Club, showing the Musick Point Radio Station buildings as they are today.