Marine shipping until the early 1990s used mainly analog signals in the VHF band, channel 16 the distress frequency on FM and then we had the CW transmissions on MW or MF from 410KHz (RDF) to 512Khz, the 500KHz frequency was allocated to calling and distress, the 512KHz used when distress was underway on the 500KHz frequency. The radio telephone band distress frequency was on 2182KHz. All long range communication was on HF, which comprised the following bands 4, 6,8, 12, 16, 22 and 25MHz. The 25MHz band was rarley used though – often only when there was heavy sunspot activity. Read up about radio propogation here -> http://en.wikipedia.org/wiki/Radio_propagation. For those that may be interested though, this article is about the older receivers of the time. It was an interesting time to be involved in radio communication between 1980 and 1990 because of the switchover from terrestrial broadcast to satellite. Communication officers at sea, the radio operator or radio officer had to go through training and qualify before he could get his sealegs. This involved learning about procedures at sea, radio communication theory and of course morse code. As time went by there was more theory thrown in because of technological changes and of course the communication officer now became an electronics officer. Many radio operators found themselves been pushed into the role of ship’s electrician after undergoing comprehensive training. I left at about this time mainly because I felt 10 years at sea was all I could handle although to be brutally honest those were the best years of my life.
The Radio Room
The radio office right throughout the 20th century was dedicated to communication and Safety of Life at Sea (SOLAS). Morse code remained the chief means of communication from ship to shore and vice versa until about 1999 and/or INMARSAT became the choice internationally. Actually by international law but who cares. Although morse code may seem to be a thing of the past this stream of dots and dashes are still used and are part of the curriculum for navigating officers. In fact radio beacons often still use very slow morse transmissions to identify themselves. VORs (voice operated radio beacons) are becoming more common. The military use morse still extensively in intership communication via light through the use of an Aldis lamp or Heliograph.
The radio room in the 70s and 80s consisted of two receivers, one of which was known as the emergency receiver and could run on batteries. There were two transmitters, one which covered all the marine bands, essentially 400W on the 410-512KHz, 2MHz bands and up to 1500 watts Peak Envelope Power in single sideband suppressed carrier mode. SSB was a major advance in the 70s whereas before communication was more or less done solely on double sideband and carrier wave. CW is a term often used by operators communicating via morse code. In the radio room there was a two tone alarm, an automatic receiver used to detect signals on the 2182KHz frequency. The emergency alarm on 2182KHz consisted of two audio frequencies 1330/2200Hz modulating the 2182KHz carrier frequency. The other automatic alarm receiver was the 500KHz alarm – this activated after detecting 12 4sec long dashes with one second spacing. This receiver would normally set off alarm bells, one set being in the RO’s cabin. The radio office also had switchovers for the different antennae, one being a long wire antenna for reserve use (or emergency). A 500KHz alarm been set off at sea was often very dramatic – and the repercussions very often had a very sad ending to a life or lives at sea. The radio room also had the necessary sending devices, the two tone alarm generator and the Auto Keying Device known as the AKD which sent the 4 second dashes.
Last but not least was the lifeboat radio – a hand cranked (generator) radio transceiver which operated on the 500KHz and 2182KHz frequencies.
The company I worked for had radio telex installed in the mid 80s and this was a boon to the R/O but also served as a warning for things to come. Radio telex communication was duplex. As the ship’s main transmitter (actually all radio equipment for that matter) was synthesised through a Phase Locked Loop system for accurate frequency generation, it was rare that telex signals would end up being corrupt. Telex then also used Foward Error Correction so don’t think this is a modern term. 
Manufacturers
We didn’t use an extensive range of manufacturers in this department, sticking strictly to Marconi for the French and Italian built ships and JRC for everything else. Yes there was Hagenuk equipment on the one German vessel they owned. The newer JRC (Japanese Radio Company) equipment was stunning but my favourite of course was the Marconi Conqueror 1500W PEP transmitter and Apollo receiver which I am sure many a British R/O would fondly remember.. The JRC auto-tuning transmitter I found to be highly suspect – fortunately they used forced air cooled valve output stages, if they were to have used transistors I doubt that they would have worked for very long – most of the ships I sailed on had faulty auto-tuning and it was an endless battle to re-configure them because the manuals were in Japanese English. I think that more often than not the R/O was not bothered with this state of affairs – manually tuning a transmitter was not difficult. (actually years later I came across a guy that used to tune his 25W Bekker transmitter for maximum cathode current – this was on a trawler. When I showed him that one tunes for a dip to get resonance he couldn’t believe the communication differences on his next trip). Why would an R/O worth his salt want an auto-tuning transmitter anyway? I found the modern units (Skanti, used on a fishing fleet I used to service, wayyyy superior).
The Marconi Apollo Receiver – wish I could get my hands on one!
Radar
The radio officer had a pretty much relaxed time at sea and his watches were a compulsory 8-12 ship’s time in the morning and another 2 by 2 hour shifts outide this time period. I normally did the 8-12, 1300 to 1500 and 1800 to 2000 hour shifts in time to get to the pub. In those days drinking was allowed.
and the liver took an enormous beating. However as ship’s equipment is prone to the elements it was necessary to ensure that all equipment was in good state and this especially applied to also the navigation equipment. One of the main failings in those days was the ship’s radar from new to old – they always had some issue or other. Although very well made I found again the JRC radars to be the most reliable and the worst was Decca (anti-collision and very sophisticated for that era but Raytheon was better). I will explain this of course. The Decca radars which I became accustomed to used mainly solid state inverters in their power supplies. This was a fairly new technology in the 70s and 80s and of course with anything new there were always teething problems and these were no different. The switching components would often fail and like all good technicians we couldn’t wait to get the unit open to deliver some miraculous repair. However, as I was to learn in my next life as a consumer electronics technical expert, replacing just the faulty component does not always mean a permanent repair. We did not keep a lot of spares on these vessels – we kept radio spares according to radio regulations in maritime law and radar spares were sparse – magnetron, klystron, TR tube and maybe an ATR. So changing an SCR in a power supply may have meant changing a faulty capacitor as well in the snubber circuit. Not having the amenities meant not conducting a full repair i.e. NOT changing the capacitor. I remember once having to purchase diodes at an electronics repair shop in Port Elizabeth to fix our radar (Raytheon) only to find the radar failed once we left harbour. Getting a shoreside technician in once we hit Durban was an embarrasment because all he did was replace the same diodes which I had already replaced with the Raytheon suggested components. In the long run not a cheap solution keeping bare minimum of spares of course. On one ship I was lucky to be told I could strip the Captain’s TV receiver so I could get the video transistor to replace a faulty unit in a VERY expensive Krupp Atlas radar. The irony was that the K.A. radar visually displayed to the technician exactly what was wrong with it via the Plan Position Indicator (PPI i.e. CRT display). However it was the display that failed. Brilliant hey?
I had an incident once where the 15 year old JRC radar lost video – it ended up with the trigger been lost and when I scratched around to get voltages on the relevant circuitry the components fell off the PCB due to corrosion. I subsequently found some tag strip and very carefully soldered the remnants of the components back onto some tags and glued the strip into place onto the chassis and soldered wires back onto the PCB. Fortunately there no interaction and the radar fired up once again. I found out to my amazement that when the ship was sold as scrap two years later that the radar was still working although I had requested that the entire board be replaced. Such is the JRC equipment. And why the corrosion? I take my hat off to the design engineers – it had been running for 15 years without previous intervention – usually it was the transmitter that gave trouble – that unit had never been opened before. For the technically minded, I was possibly just lucky but in most cases the ship’s radar used to fail because of faulty mixing xtals or magnetron. The manuals were extensive and well written – in most cases electronic component failure was seldom and when it did happen within an hour ot two we’d be up and running again. They were after all designed for ship use and the safety factor was important.
The worst repair job I have ever seen was by a French ‘engineer’ in Marseilles. Again a power supply issue 
the engineer embarked looking a bit shaky. I had pinpointed the problem and had requested through radiogram (youngsters won’t know this word – think of an SMS sent in morse) that a replacement board be brought up. The engineer had one look, scoffed and said that this board was not faulty, but indeed ‘something else’. He left to pick up ‘something else’ and when he came back looked decidely dodgy and reeking of booze. This up and down process took place over the period of about 6 hours when finally he left with the entire transceiver. At that stage he nearly fell overboard trying to get the unit off – but was he pissed! I complained to the captain. He complained to the agents. And we got a bill for the time this drunk spent on our ship, can you believe it. Fortunately for us the next port ‘o call we had a more sober looking gentleman come down and replaced the transceiver which had been fixed by their shore staff. I’d hate to know what that bill was.
I’ll be back….