Radio silence

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In telecommunications, radio silence is a status in which all fixed or mobile radio stations in an area stop transmitting.

The radio stations include anything capable of transmitting a radio signal. Radio silence generally applies to the military, where any radio transmission may reveal troop positions, either audibly from the sound of talking, or by its use as a homing signal. In extreme scenarios Electronic Silence (EMCON) may also be put into place as a defence against interception.

In the British Army, the imposition and lifting of radio silence will be given in orders or ordered by control using BATCO. Control is the only authority to impose or lift radio silence either fully or selectively. The lifting of radio silence can only be ordered on the authority of the HQ that imposed it in the first place. During periods of radio silence a station may, with justifiable cause, transmit a message. This is known as Breaking Radio Silence. The necessary replies are permitted but radio silence is automatically re-imposed afterwards. The breaking station transmits its message using BATCO to break radio silence.

The command for imposing radio silence is "Hello all stations, this is 0. Impose radio silence. Over."

Radio silence can also be maintained for other purposes, such as for highly sensitive radio astronomy, or in marine communications to allow faint distress calls to be heard, see Mayday. In the latter case, the controlling station can order other stations to stop transmitting with the proword "SILENCE SILENCE SILENCE". (The word uses the French pronunciation, "see-LAWNCE."). Once the need for radio silence is finished, the controlling station lifts radio silence by the prowords "SILENCE FINI."^[1]

In the USA, CONELRAD, EBS and EAS were also a way of maintaining radio silence, mainly in broadcasting, in the event of an attack.

Radio silence orders

• Radio silencing occurred after Japan attacked Pearl Harbor in World War II, having used AM radio station KGU in Honolulu as a homing signal.
• On June 2, 1942, during WWII, a nine-minute air-raid alert, including at 9:22 pm a radio silence order applied to all radio stations from Mexico to Canada.

References

See also

• Guard band
• EMCON
• The Zone of Silence
• United States National Radio Quiet Zone