Two-way radio

Other two-way radio systems operate in full-duplex mode, in which both parties can talk simultaneously.

[4] The first truly mobile two-way radio equipment was developed in Australia in 1923 by Senior Constable Frederick William Downie of the Victorian Police.

The Victoria Police were the first in the world to use wireless communication in cars, putting an end to the inefficient status reports via public telephone boxes which had been used until that time.

The first sets occupied about half of the floor in the back seat of the Lancia patrol cars.

Part of APCO Project 16 set standards for channel access times and delays caused by system overhead.

A transmitter at the tank site continually sends a signal with a constant audio tone.

A meter at the remote end would vary, corresponding to the tone pitch, to indicate the amount of water present in the livestock tank.

This type of radio system serves a purpose equivalent to a four-to-twenty milliampere loop.

Some systems multiplex telemetry of several analog conditions by limiting each to a separate range of tone pitches, for example.

These models will be backed-up by drive testing and actual field signal level measurements.

[15] In government systems, equipment may be replaced based on budgeting rather than any plan or expected service life.

[17] Another source says system backbone equipment like consoles and base stations are expected to have a fifteen-year life.

[22] There are other factors that affect the range of a two-way radio such as weather, exact frequency used, and obstructions.