[ARC5] 500 kHz Emergency Frequency

[Mike Morrow]

> A friend of mine has a clock that came off a ship.  It has red
> pie shaped areas marked to indicate the periods when you were
> to shut down your transmitter and listen for distress calls.

I've got a Seth Thomas model from WWII, U.S. Maritime Commission.
They are not inexpensive, but they are soaked in history.

The traditional maritime radio room clock, located on the radio
console, has red wedges between 15 to 18 minutes and 45 to 48
minutes past the hour.  Those were the silent periods in which
ALL traffic would cease to monitor 500 kHz for distress calls.

Another very important marking on the outer edge of the clock
face is 12 red bars four seconds in length, separated by one
second.  That was to aid the operator in manually sending the
*real* maritime Morse distress signal that triggered the
auto-alarm receivers of other stations on 500 kHz.  Normally,
a motor driven device would generate these auto-alarm dashes.

The auto-alarm receiver was put in service when the operator was
not on station, and it activated alarms on the bridge and in the
operator's berthing upon receipt of a series of these four-second
dashes for more than a minute.

The auto-alarm signal was very distinctive and rare, so it was more
attention-getting than the standard ...---... call.  You can tell
that by listening to the mp3 recording of a real distress signal
below.

An interesting web page at http://www.qsl.net/n1ea/ describes the
communications from the passenger liner Prinsendam (Call PJTA) on
4 October 1980 as she was on fire and sinking near Alaska.  NS1L
and N1EA were Radio Officers on the Williamsburgh (Call WGOA) that
came to rescue after the distress call was intercepted.  Here is
the actual recorded 500 kHz traffic beginning with the Prinsendam's
auto-alarm signals, whose four-second dashes can be heard clearly
after the first 25 seconds:

  http://www.qsl.net/n1ea/sos_de_pjta_small_file_size.mp3

Technically speaking, the Prinsendam operator sent SOS incorrectly,
as ... --- ... ! The manually keyed Morse is slow, at about 10 wpm.
 
Back to clocks:  More modern clocks also had three-minute green wedges
00 to 03 and 30 to 33 minutes past the hour indicating the times to
listen for distress calls on 2182 kHz phone.

These clocks were legally required by FCC in 47CFR83.201, which no
longer exists.

> I guess there is an effort underway now to make 500 KHZ an amateur
> frequency.

There has been, and there are still some FCC STAs for such operation.
It'll all be replaced and regularized with the new 630m band allocation
approved by WARC last February, as described in this ARRL notice:

"It’s official -- delegates attending the 2012 World Radiocommunication
 Conference (WRC-12) have approved a new 7-kilohertz-wide secondary
 allocation between 472-479 kHz for the Amateur Radio Service. Agenda
 Item 1.23 had both its first and second readings in Plenary Session
 on Tuesday, February 14; to become part of the ITU’s Radio Regulations,
 each Agenda Item must be read twice in Plenary Session. While the Final
 Acts will be signed on Friday, February 17 at the close of the Conference,
 the new allocation will not take effect until it is entered into the Radio
 Regulations. No date has been set for this, but it is unlikely to be earlier
 than January 1, 2013. In any case, no amateur can use the band until his or
 her national regulations are revised to implement the allocation."

Sure, seven kHz doesn't sound like much, but in terms of percentage of
the operating frequency, it's as wide as 52 kHz at 3.5 MHz or 207 kHz at
14 MHz.

In the mid-1960s I first got interested in the mysterious Morse signals found
in the 405 to 535 kHz maritime band by copying stations on my first piece
of military gear, a BC-453-B.  For about 20 years before maritime Morse ended
in 1999, I kept a receiver at bedside on 500 kHz.  Night-time reception could
be very interesting, not just on 500 kHz.  Coast stations like WCC, WNU, WLO,
NMO, KPH, etc. had their assigned frequencies, and ship stations used a
limited set of working frequencies on 425, 454, 468, 480, and 512 kHz.

Much more information is available at http://radiomarine.org/ .

The MF maritime Morse band was the most interesting segment of the radio
spectrum...I miss it greatly.

Mike / KK5F