NMO - Part 4 - Procedures
by Jeffrey Herman
All rights reserved.
Part 4. Procedures
4A. Silent Periods (SP)
The first thing an op coming on watch does is to check his clock against
WWV (ITU regs!), for certain actions on 500 have to be timed down to the
second. In the log it goes:
OBTAINED WWVH TIME TICK - CLOCK CORRECT 2500KC 0900Z
Because of the steady stream of signals on 500 a weak station sending a
distress msg might not be heard. And at one time, calls AND traffic were
passed on 500 - there was no shifting to working frequencies to pass
messages. Thus silent periods were created. These consist of two
three-minute intervals, in which worldwide no one transmits - volume
controls are turned up - ears are pressed to the speaker grill - one's
breath is held, from minute :15 to minute :18, and again from minute :45
to minute :48. Even traffic being passed on working frequencies would
stop. For example, if I were sending the WX on 440kc:
...HIGH PRESSURE 1028MB 35.8N 132.3W BT CQ CQ CQ DE NMO AS SP SP AR
at which point myself and my listening audience would shift back up to
500 for that particular 3 minutes.
Whoa to the station whose clock is off or who forgets the SP, for a half
dozen stations might jump on him:
VLA VLA VLA DE 3FWR 3FWR K
QRT SP SP
(the ship 3FWR calls the shore station VLA - someone breaks in to tell
him to stop transmitting; he responds with `sorry' and is still scolded,
says he's sorry a second time, and is scolded again),
although someone somewhere in the Pacific was more direct and to the
JNKB JNKB DE FHWN FHWN
SHUT UP SP (at 30 wpm)
Now, the last 15 seconds of a SP was set aside for safety and urgent
From the lowest to the highest priority, the following types of
CQ - meaning ``Hello All Ships and Stations'' sent in a 3X3 format:
CQ CQ CQ DE FUM FUM FUM WX AND TFC LIST QSW 430 AR
Here, the shore station FUM, French Navy Tahiti, makes an announcement
that he'll be sending the weather and his traffic list on 430 kc.
The CQ is the most common broadcast announcement; one will go out every
TTT - this is the prosign for a safety broadcast: storm warnings,
navigation hazards, or anything involving the safety of shipping:
TTT TTT TTT CQ DE ZLW ZLW ZLW CYCLONE WARNING NR 38 QSW 475 UP
Each T is longer than usually sent to provide a very distinctive sound.
During the last 15 seconds of a silent period a half dozen TTT's would
be going out. In particular, the shore stations running around the
perimeter of Australia would sent the same TTT, one station following
the previous station. Everyone in the Pacific wanted to be the first
one out with their TTT announcement instead of waiting for a station
1000 miles away to finish, so many time they'd all go out at once.
What a mess!
XXX - this prosign is indicative of an urgent broadcast where shipping
and lives might be in danger (the CO might order the auto alarm sent
prior to the preliminary announcement on 500):
XXX XXX XXX CQ DE NMO NMO NMO HURRICANE WARNING QSW 440 AR
Again, each X is drawn out so as to provide a very distinctive sound.
This, as with the TTT announcements, went out during the last 15
seconds of a silent period. Those sending a TTT were supposed to give
way to an XXX (remember, everyone is working duplex or full QSK -
you MUST be able to hear anyone sending under you).
SOS - the darkest hour of an ops career is when the Captain of the ship
enters the radio shack, hands the op a piece of paper, and says ``Send
the SOS - here's our position''. International procedures dictate
*every* step the operator will take:
4C. Distress Proceedures:
1. Auto Alarm (AA): twelve 4-second dashes, each dash followed by a
one-second pause, sent in A2 (modulated CW). ITU regs demand that every
ship carry an AA decoding receiver; this decoder will ONLY respond to
AA's sent in A2.
1A. In A2 the transmitter is modulated by a tone (two meter repeaters
ID in this manner). Thus, what you would hear on your receiver, with
your BFO on would be several tones, or harmonics - very musical and an
attention getter; a station sending CW in A2 sounds like someone
sending code on a piano keyboard by pressing a half dozen keys at once!
[One very old book in my collection describes an easy (but archaic)
method of modulating a CW transmitter: a toothed wheel is rotated at
several hundred RPM with a wiper, connected to the keying circuit of
the xmtr, rubbing over the teeth of the wheel. Crude but effective.]
The AA will activate the decoder on board every ship within receiving
distance after four correctly sent dashes are received; the decoders
are designed to be a bit forgiving concerning the timing of the AA dash:
they will accept, as a valid dash, a dash of between 3.5s and 6s in
length (just in case the sending op is nervous!). As mentioned, only
four correct dashes are needed, but just to be sure, ITU demands that
twelve be sent. Once the AA decoder receives four dashes its latching
relay closes activating lights and bells in the radio room, the radio
officer's stateroom, and up on the bridge.
2. The op in distress now must wait two minutes (if possible - if his
feet are getting wet then he skips this step) for off duty ops, on
board other ships that have received his AA, to get to their radio
rooms. 500 kc is now in a continuous silent period until the controlling
CQ CQ CQ DE (cs of controlling stn) QUM 500 KC VA
Note that QUM = Distress traffic has ended - resume normal traffic.
The controlling station is the distressed vessel - he can and does
give control to the first responding shore station; thus if I was
the first shore stn to respond then NMO would be the controlling stn.
Woe to ANY ship or shore station who xmits normal traffic during a
9JBV 9JBV DE HCKO HCKO HW OM K
QRT QRT QRT SOS 500 (sent by dozens of stations)
3. The distress broadcast.
All traffic pertaining to the distress will be sent on 500. Those not in
a position to assist will move to 512 kc - 512 is the alternate calling
freq when 500 is in distress use. Here is a typical distress broadcast
(sent at no more than 16 wpm (ITU regs!)):
SOS SOS SOS CQ DE 5TER 5TER 5TER BT SOS 281751Z MV PANAMA TRADER
TAKING ON WATER ENGINE ROOM FLOODED POSN 13.73N 152.55W 13.73N 152.55W
NEED IMMEDIATE ASSISTANCE AR MASTER SOS
This broadcast would be followed by a 10 second long dash to aid
receiving stations in getting a bearing to 5TER's position.
Then would come the acknowledgements:
SOS 5TER 5TER DE NMO NMO NMO R R R SOS
SOS 5TER DE KFS KFS KFS R R R SOS
SOS 5TER 5TER 5TER DE JNA JNA JNA R R R SOS
SOS 5TER 5TER 5TER DE WNPH WNPH WNPH R R R SOS WE ARE IN POSN 11.81N
151.32W CHANGING CSE TO UR POSN WILL GET ETA K
SOS WNPH DE 5TER R TU HERE IS MORE INFO .....
The first thing you'll notice is that ALL transmissions MUST start with
SOS (ITU regs!). What happened here is that three shore stations QSL'd
the distress broadcast - ITU regs state that you must send R R R SOS; a
nearby ship also QSL'd and is proceeding to 5TER's posn. The 500 op at
NMO (me!) would be on the phone to RCC (Rescue Coordination Center)
passing all info - RCC would launch aircraft and also key up the AMVER
computer to check for nearby vessels. Suppose the AMVER computer shows
that KPLH is steaming nearby:
SOS KPLH KPLH KPLH DE NMO NMO NMO
would be sent every 5 minutes both on 500kc and on all the HF freqs.
In case no ship responded to 5TER's distress call, 5TER might give
control to NMO. We would then periodically send:
DDD SOS SOS SOS DDD CQ DE NMO NMO NMO BT
where the DDD indicates that NMO is relaying a distress.
4d. Other Broadcasts
I had mentioned that the last 15 seconds of the silent period were
reserved for safety (TTT) and urgent (XXX) preliminary broadcasts. The
problem was that 10 or 20 shore stations might have such a broadcast to
put out and none of them knew who else would be a sending one - the
result was sometimes a mess. To hear a dozen shore stations trying to
send at once:
TTT TTT TTT CQ DE ... was extremely funny!
Thus, some would start a bit earlier than H:17:45 or H:47:45. I would
start hearing TTT TTT TTT CQ DE ... sometimes as early as the last
30 seconds of an SP. Now, EVERY shore station worked duplex and everyone
wanted to be the first to get their broadcast out. The Japanese stations
were always the most polite. I'd hear a New Zealand TTT and an Australia
TTT and a Japanese TTT and the Japanese station would always stop his
broadcast to yield to the others. Once the freq was quiet then the
Japanese station would start his TTT prelim again.
Oh, a prelim broadcast is the short announcement on 500 telling everyone
to shift to one's working freq for the full broadcast text:
XXX XXX XXX CQ DE VLA VLA VLA URGENT MARINE BCST MAN OVERBOARD QSW 472 UP
is a prelim broadcast.
The Australian shore stations were a well-behaved unit (even though they
might crush other countries trying to send prelims!). The following
Aussie stations would take turns sending their prelims - as soon as one
finished the next would start:
VII, VIA, VIR, VID, VIS, VIT, VIM, VIB.
The only New Zealand shore station I used to hear was: ZLZ. Other South
Pacific shore stations I heard nightly were:
FJP - New Caledonia
3DP - Fiji Islands
P2M - Papua New Guinea
DUQ - Samoa
8BB - Indonesia
VJZ - New Britain
FUM - Tahiti (French Navy)
XSU - can't remember - used to hear a lot of X__ shore stations,
and ones from Korea, Philippines, China, Central and South America...
North Pacific West Coast shore stations that would boom in nightly
NMQ - USCG Radio Long Beach CA
NMC - USCG Radio San Francisco CA
NOJ - USCG Radio Alaska
KSF - San Francisco commercial station
KPH - another San Francisco commercial station
KHK - Honolulu commercial station
KOK - Southern California commercial station
To hams, 500 would have been a DX'ers dream but we took the excellent
conditions for granted. Keep in mind that NMO had a *very* long longwire
receiving antenna (over one mile in length).
Not only would there be pile ups at the end of a silent period, but
also at the top of each hour; that's when the low priority
``CQ CQ CQ DE ... WX AND TFC LIST QSW ... AR'' type of prelims would
go out. So, not wanting to take a number and wait for others, prior to
sending a prelim broadcast I would always send: dit dit dit (or I E)
(i.e. .. . ) as a way of saying ``Hey - don't anyone else send anything
because I'm running 10 thousand Watts and in A2 and I'll crush you...''
or something like that. Seriously, if I had a safety or urgent to send
at the end of an SP, as I was sending my TTT or XXX I'd hear other
countries under me as they started their prelim and they would suddenly
stop when they heard us; NMO must have put out a commanding signal to
the entire Pacific for everyone to yield to us.
Generally, 500 was very orderly and everyone was a gentleman.
4e. Frequency scheme.
Ships had a choice of using any of the following working frequencies:
425, 454, 468, 480, and 512 kc. Shore stations only had one fixed
working freq, so during an initial call on 500 a shore station would
give his working freq and the ship would choose one of the above to get
as close as possible (so as to work duplex):
3LF 3LF 3LF DE CKHB CKHB TR K
CKHB DE 3LF GE QSW 471 K
DE CKHB R 471/480 UP
Here, the ship CKHB called the shore station 3LF wanting to pass a
travel report (TR); 3LF has a fixed working freq of 471 so the ship
chose to use 480: 471/480 means ``you use 471 and I'll use 480''.
Why these particular choice of frequencies? Note that 454 kc
was the old 660 meter wavelength, 480 kc = 625 meters, and
of course, our star frequency 500 kc = 600 meters.
Oh, if you haven't guessed, shore stations have 3 character callsigns,
and ships have 4 character calls.
Many folks have shown their surprise that this kind of activity was
occurring, on a worldwide scale, just below the broadcast band. But as
a young pup I knew something was lurking just below the rock and roll
band; living near NMQ (USCG Radio Long Beach, CA) I would occasionally
hear an unusual on-and-off hissing sound which would get stronger the
lower I tuned:
sheeeesh shesh sheeeesh shesh sheeeesh sheeeesh shesh sheeeesh
(NMQ sending their CQ - of course my AM table top tube radio didn't
have a BFO). That prompted me to both study the code and take the cover
off my AM radio to move to `down' to the source of this noise (boy did
I ever ruin that radio; thank goodness my parents bought me a Heathkit
shortwave receiver - with a BFO).
End of Part 4.
Jeff KH2PZ / KH6