Mike, Interesting! I didn 't know you collected lifeboat radios! One of the neatest ones I remember was the little Marconi one whose name I cannot recall now. It came after the big heavy clumsy one they had named the "Salvita" or "Salvor" . My memory of it is too fuzzy now, too many years ago! Anyway it was in a rectangular case about same height and width of a shoebox but about two and a half times longer! I did 8364 and 500 khz CW/MCW and A3 voice on 2182. There was a Swedish set that was very nice for it's size,I think made by STC. It had a receiver for 8 mhz that tuned a limited band for CW and lots of tankers had two of them. One in the lifeboat and one in the forecastle of the ship. Several ships I did inspections on had an emergency antenna erected for that set, so it could be used to communicate during emergencies, if the tanker broke into two parts (which happened several times I gather) and left people stranded on the floating bow of the ship! It was reassuring when I did an inspection and actually called WNU Slidell on 500 khz and raised him for the test. It was easy enough to crank and work the key single handed. With the old RCA and Mackay sets it took 2 people to operate one of those, one cranking one operating.
If they were still in use, I'd imagine one could build a tiny radio now capable of more than the old tube stuff that used to be around then. Mackay built a solid state lifeboat set, but it was an awkward thing to use and could have been much smaller and lighter for what it was. 73 Sandy W5TVW -----Original Message----- From: Mike Morrow Sent: Saturday, April 14, 2012 5:56 AM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] A Real SOS (OT) Ron wrote: > By 1980 receivers had grown very selective, but the fact was that a great > many ships still used a regenerative receiver as the "backup" in case the > main receiver was out of commission for some reason. The auto-alarm (AA) receivers were also designed to be broad enough to detect A2 (MCW) distress AA signals from 492 to 508 kHz. Typically the AA receiver was a dedicated unit of TRF design feeding simple electronics capable of detecting the distress auto-alarm signal of twelve four-second dashes with one-second spacing sent in one minute's time. The AA signal is one of the most interesting portions of the distress signal in the link to the Morse traffic containing the M/V Prinsendam/PJTA SOS. I recommend the web page ( http://www.qsl.net/n1ea/ )of N1EA, the assistant radio officer on the US merchant ship ship Williamsburg/WGOA that came to the rescue from 120 nm away after hearing the SOS DE PJTA signal. More details and background are provided, along with direct link to an MP3 version on the SOS traffic by clicking the SOS DE PJTA button on that page. Apparently, the decision to send the SOS was made by the Prinsendam's chief radio officer, Jack van der Zee, and not the ship's master. Very unusual! Also, the QRZ.COM page for the chief radio officer on the Williamsburg has a lot of interesting related information: http://www.qrz.com/db/ns1l Both radio officers of the Williamsburg are hams (NS1L, N1EA). > Some of the signals in the link below sound like they have modulation. > They > do. MCW was the norm for emergency traffic so they could be copied even on > a > receiver without a BFO. Even the emergency lifeboat transmitters like the SCR-578 and AN/CRT-3 and commercial equivalents, plus all the larger lifeboat emergency receiver and transmitters like the RCMA ET-8053 (AN/SRC-6) and the Mackay 401-A (AN/SRC-6A) sent MCW on 500 kHz. That actually complicated their design and increased the power consumption (generated by a human on a hand-crank), compared to a simple A1 transmitter. (I collect these sets.) > The possibility of an SOS not being heard at all in the bedlam is what > launched the twice-hourly "silent periods" when all ships fell silent and > the R.O.s listened on 500 kHz for three minutes. Yep, from minute 15 to 18 and 45 to 48 each hour. Any Morse traffic being sent on ANY maritime frequency MF or HF would be paused with a "AS SP" when minute 15 and 45 came up on the clock so that ROs on any frequency could turn their attention to 500 kHz. The old MF 405 to 535 kHz Maritime Morse band was an amazing place at night. For years I kept a bedside receiver tuned to 500 kHz. > This link is a real SOS recorded in 1980 when the MV Prinsendam had an > engine room fire and a flooded engine room. It begins with a series of > long > dashes. That was the standard opening that was supposed to set off > automatic > alarm bells on any vessels whose radio rooms were not operating at that > moment. The bells went off on the navigating bridge and right over the bed > were Sparks would be sleeping. Following the dashes the SOS and emergency > message begins. > > http://mikea.ath.cx/www.n1ea.coastalradio.org.uk/EJM_CD3_Track03_SOS_de_PJTA.zip It has always been interesting to me that the radio officer on the Prinsendam, technically did *not* send the SOS correctly. It's supposed to be sent as as one very distinctive signal of ...---..., yet PJTA sent ... --- ... with definite space between the S, the O, and the S. But in reality, it's those four-second dashes of the AA signal that draw the most attention! Technology did not move very fast in the communications of the merchant marine. When I took my Second Class Radiotelegraph exam in 1981, the exam material was dated 1961 and required schematic drawing and short answers in addition to multiple choice. I never felt the elation of passing any other FCC exam that I got after passing the commercial radiotelegraph exam. Merchant marine MF Morse signals were, IMHO, the most interesting signals found on the air. In high school in the mid-1960s I used a military surplus BC-453-B command set receiver to copy those signals. I'll be very interested in the KX3's capabilities on the new MF band, even though the maritime signals are long gone. 73, Mike / KK5F ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ----- No virus found in this message. 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