Radio Silence Clock?

[nigelmercier]

I've recently seen a clock that "... features the 4 silent zones to indicate that for 3 minutes after the hour, the 1/2 and each quarter that radio silence should be made, so that distress calls can clearly be heard by the emergency services".

I don't recall this mandate when I did my VHF course, is it widely practiced?

http://www.piratescave.co.uk/?searchStr=TA0761

 

[Simondjuk]

It's a practice stemming from the days of poor long distance communications. It gave a chance for anyone in distress and on the limit of transmitting range to, perhaps, have their weak signal heard.

It's not taught as it's neither mandatory or particularly observed anymore, perhaps other than as a matter of tradition in some quarters.

 

[lpdsn]

Presumably it was practice with long range morse communications, not VHF.

 

[Pye_End]

I vaguely remember it was part of the syllabus when I first took the VHF test, but was certainly not brought up when doing the DSc course recently.

 

[Roberto]

the 0000-03 0030-33 minutes are for silence in MF/HF marine frequencies, the 0015-18 0045-48 were for silence in Morse marine frequencies

 

[prv]

I don't recall this mandate when I did my VHF course, is it widely practiced?

It's from the days of radio officers and morse across distant lonely oceans, not yotties nattering away on VHF, nor Inmarsat emails in modern shipping.

Pete

 

[starboard]

Remember it well from my early Lifeboat days using the big MF set...........All stations using 2182 kHz were required to maintain a strictly enforced three-minute silence and listening period twice each hour, starting at h+00, h+30. This allowed any station with distress, urgent or safety traffic the best chance of being heard at that time, even if they were at some distance from other stations, operating on reduced battery power or perhaps reduced antenna efficiency, as for example from a dismasted vessel. As a visual aide-memoire, a typical clock in a ship's radio room would have these silence periods marked by shading the sectors from h+00 to h+03 and from h+30 to h+33 in green. Similar sectors were marked in red for what used to be the corresponding silence and listening period on 500 kHz between h+15 and h+18 and from h+45 to h+48.[4] These silence periods are no longer required as the introduction of GMDSS has produced alternative automatic watchkeeping systems and the 500 kHz band is no longer in use for maritime traffic.

 

[nigelmercier]

Thanks for the replies. Good to see Plastimo keeping up with the times.

 

[Simondjuk]

Starboard, what a fantastically comprehensive reply. Thank you for proving me with a full, rather than very vague, understanding of it.

 

[PilotWolf]

Is the MF/HF one not still required? Even with watch alarms? It certainly was when I did my GRC but that was mid 80's!

Also used to love listening to morse from Portishead (IIRC) as a very young SW listener.

W.

 

[maby]

Is the MF/HF one not still required? Even with watch alarms? It certainly was when I did my GRC but that was mid 80's!

Also used to love listening to morse from Portishead (IIRC) as a very young SW listener.

W.

I've seen it mentioned recently, but don't remember where.

 

[Barnacle Bill]

I believe it still applies on MF: 2182 KHz (which is like 'VHF channel 16') from 00 to 03, 30 to 33.

 

[Roberto]

I was curious and just checked the ITU documents


The 2012 Radio Regulations (the official rules) only cover GMDSS and make no mention of the 2182 silence period.

Resolution 354 of the World radio conference 2007 addresses

RESOLUTION 354 (WRC-07)
Distress and safety radiotelephony procedures for 2 182 kHz
The World Radiocommunication Conference (Geneva, 2007),
noting
a) that all ships subject to the International Convention for the Safety of Life at Sea
(SOLAS), 1974, as amended, are required to be fitted for the Global Maritime Distress and Safety
System (GMDSS);
b) that some vessels not subject to SOLAS, 1974, as amended, may not be making use of
the techniques and frequencies of GMDSS prescribed in Chapter VII and may wish to continue
using radiotelephony procedures for distress and safety communications on 2 182 kHz until such
time as they are able to participate in the GMDSS;
c) that some administrations may have a need to maintain shore-based radiotelephony
distress and safety services on 2 182 kHz so that vessels not subject to SOLAS, 1974, as amended,
and not yet using the techniques and frequencies of GMDSS will be able to obtain assistance from
these services until such time as they are able to participate in GMDSS,
considering
that there needs to be some recognized guidance for the use of radiotelephony on 2 182 kHz for
distress and safety communications,
resolves
1 that ships, when in distress or when engaged in urgency or safety-related
communications on 2 182 kHz, use the radiotelephony procedures contained in the Annex to this
Resolution;
2 that coast stations, in order to maintain communication with non-GMDSS ships that are
in distress or engaged in urgency or safety related communications on 2 182 kHz, use the
radiotelephony procedures contained in the Annex to this Resolution.


The Annex makes no mention of silence periods, not in the "Availability of frequency", nor in "Protection of freq", nor in the "Watch on the freq", etc



Older ITU documents indeed show both the silence periods for Morse and MF.

 

[JumbleDuck]

I vaguely remember it was part of the syllabus when I first took the VHF test...

Same here. Twenty five years ago, in my case.