The necessary replies are permitted but radio silence is automatically re-imposed afterwards. During periods of radio silence a station may, with justifiable cause, transmit a message. The lifting of radio silence can only be ordered on the authority of the HQ that imposed it in the first place. Control is the only authority to impose or lift radio silence either fully or selectively. In the British Army, the imposition and lifting of radio silence will be given in orders or ordered by control using 'Battle Code' ( BATCO). In extreme scenarios Electronic Silence ('Emissions Control' or EMCON) may also be put into place as a defence against interception. Military Īn order for Radio silence is generally issued by the military where any radio transmission may reveal troop positions, either audibly from the sound of talking, or by radio direction finding. Up until the procedure was replaced by the Global Maritime Distress and Safety System (Augin the U.S.), maritime radio stations were required to observe radio silence on 500 kHz (radiotelegraph) for the three minutes between 15 and 18 minutes past the top of each hour, and for the three minutes between 45 and 48 minutes past the top of the hour and were also required to observe radio silence on 2182 kHz (upper-sideband radiotelephony) for the first three minutes of each hour (H+00 to H+03) and for the three minutes following the bottom of the hour (H+30 to H+33).įor 2182 kHz, this is still a legal requirement, according to 47 CFR 80.304 - Watch requirement during silence periods. Again, disobeying such an order is extremely dangerous and is therefore a criminal offence in most countries. "Distress traffic ended" is the phrase used when the emergency is over. The aviation equivalent of Seelonce Mayday is the phrase or command "Stop Transmitting - Distress (or Mayday)". Once the need for radio silence is finished, the controlling station lifts radio silence by the prowords "Seelonce FINI." Disobeying a Seelonce Mayday order constitutes a serious criminal offence in most countries. (The word uses an approximation of the French pronunciation of the word silence, "See-LAWNCE.").
In the latter case, the controlling station can order other stations to stop transmitting with the proword "Seelonce Seelonce Seelonce". Radio silence can be used in nautical and aeronautical communications to allow faint distress calls to be heard (see Mayday).
#Period of radio silence manual
Radio room clock, showing the 500 kHz silence periods (red wedges), the 2182 kHz silence periods (green wedges), and alternating red and white bars around the circumference to aid manual transmission of the 4-second SOLAS signal. CQ like calls (to see who is out there) should not take place until after 4 minutes after the hour.
Priority transmissions should begin with the LITZ (Long Interval Tone Zero or Long Time Zero) DTMF signal for at least 5 seconds. A ham in a remote location may be able to relay emergency information through another wilderness ham who has better access to a repeater. The Wilderness protocol (see page 101, August 1995 QST) calls for hams in the wilderness to announce their presence on, and to monitor, the national calling frequencies for five minutes beginning at the top of the hour, every three hours from 7 AM to 7 PM while in the back country. The Wilderness Protocol is now included in both the ARRL ARES Field Resources Manual and the ARES Emergency Resources Manual. The Wilderness Protocol recommends that those stations able to do so should monitor the primary (and secondary, if possible) frequency every three hours starting at 7 AM, local time, for 5 minutes starting at the top of every hour, or even continuously.
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