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Marconi International Marine Company of Chelmsford, Essex.

Various bits of kit used on the ships on which I was a Radio Officer.

Transmitters:

The famous Oceanspan VII.

Designed during the Second World War and with a few refinements after, the Oceanspan was all valve transmitter with three 807s as the final output stage giving 75 watts or (optimistically) 100 watts.

The BLUE dials on the right were all the MF settings and the RED dials were for HF. It was all crystal controlled and therefore relatively fixed frequencies.

The MF frequencies (CW Only) were normally:


410kc/s, 425kc/s, 454kc/s, 468kc/s, 500kc/s and 512kc/s and were selected by the lowest blue switch.

The Black switch on the right hand side was to select the ‘metering point’.

The RED side was for HF and could select the BAND,

4/6/8/12/16/22Mc/s

Another of the RED switches chose the crystal for the selected band. The dials above are for aerial tuning.

The aerial connection was via the ceramic spout on the top of the transmitter. This would normally be a copper (quarter inch pipe if I remember correctly) uninsulated connection to the Aerial Switching unit.


The aerials were typically a main aerial which was often a high ‘T’ aerial slung between the two masts of the ship. The reserve or emergency aerial was connected to just about anything, slung between just about anything and was often not that good.

On AC powered ships there was a big transformer in the base unit but on DC powered ships this was replaced by a large electric motor taking DC in and supplying AC out. This had to be started before the transmitter was needed and made a horrendous noise (audibly).


Main Receiver:

The Marconi Atalanta receiver:

Receive range: 15kc/s to 28Mc/s in ten switched bands. 16kc/s was used for the Rugby (MSF) time signals.

IIRC 31 valves (not necessarily 31 valve envelopes as there may well have been some double triodes etc.) The user manual for the Atalanta Receivercan be found HERE

‘Lifeguard’ Auto Alarm

The Auto-Alarm was always on watch during the times that the Radio Officer was not.

It was tuned to one frequency - 500kHz to listen for Auto-Alarm distress signals. The Auto-Alarm distress signal was transmitted as twelve, four second dashes spaced by one second. The Auto Alarm would listen and when a signal was received would start to time. If it received a 4 second dash it would then go on to look for the next and so on. Any time it received four, four second dashes it would ring the bells to alert the Radio Office that there was a distress in progress. If the second, or subsequent signals proved not to be the correct sequence of four second dashes, the unit reset itself.

As you can imagine, with static in the tropics these things were always going off in error.

Another function that the Auto Alarm had was that of being a watch-keeping receiver for 500kHz. This was a necessary function when the Radio Operator was busy on HF as a 500kHz watch was required, particularly during silence periods. The Auto Alarm normally used the emergency aerial as its receive aerial.

The "Lifeguard" was designed and installed in about 1965. The operator could either hear the signals via a built-in loudspeaker or use headphones.It was only tuned to 500kHz and could operate in A1 (CW) or A2 (MCW) modes, thus it had its own built-in BFO.

It was populated with valves:  2 x EF85, 1 x E83F, 5 x D77, 1 x B309, 9 x E90CC, 1 x 9U8, 3 x E180CC, 1 x 6AU6, 1 x LN309.

There were alarm bells on the bridge and in the cabin of the operator. It was powered the emergency 24V DC from the batteries or from the ship’s mains.


The Radio Room Clock

The radio room clock is marked with the times of the statutory ‘Silence Periods’ shown in Red & Green.


The Red Silence Periods were for the 500kHz watch and it was a requirement of All Radio Officers that they maintain a silent watch on 500kHz for the three minutes (15-18 & 45-48 minutes past each hour). It was a requirement to make a log book entry as Silence Period Observed on every occasion.

As previously stated above, when a Radio Officer was not on watch the Auto Alarm took over that watch.


We were not required to monitor the Green Silence Periods as these were for the 2182kHz emergency frequency in the voice band. To be honest there was virtually no traffic on that band except when near the coast when there was ship-to-shore traffic.

The AKD - Automatic Keying Device (below)

The Automatic Keying Device was an electro-mechanical Alarm generator for use in the case of distress.

Inside the AKD there were three Paxolin wheels of about 3” diameter on a motorised shaft. The shaft turned the three wheels once in one minute.


The wheels had detents in their circumference and micro-switches touching so that the detents could be ‘read’.

The first wheel had detents in the pattern of:

S O S  S O S  S O S de (Ship’s Callsign e.g. GBZT twice)

The second wheel had 12, 4 second dashes with one second spaces for the Auto Alarms to trigger.


The third wheel had two 29 second dashes for DF (direction-finding) purposes.


The switch on the left under the lights selected where the transmitted signal would would be sent. The options were:

The Main Transmitter

The Emergency Transmitter

AUX (not normally used)

AA to send the signal to the Auto Alarm to test both the AKD & the Auto Alarm itself.


The switch on the right gave a choice of:

Sending the Morse code by hand

Sending just the Alarm signal

The full distress signal

To operate the AKD the ‘Start’ switch was pressed down, the motor started up and the unit whirred into action. The message from the first wheel was transmitted, the unit swapped to the second wheel and then to the third. Once the cycle was complete it went back to the first wheel and repeated the sequence until it…

Was Stopped by an operator, it ran out of power, the ship sank…

Under test (or operation of you were so unfortunate) the machine made a whirring (the motor) a clicking (the micro-switches falling into and coming out of the detents) and lights flashing in sequence to the code being sent.

A typical radio room of the time.

I must state that this is not one of mine and it is not me in the photo but it was very typical of the radio room on any Marconi radio room.

As Marconi employees we were sub-contracted to the ships along with all the gear. It was a legal requirement for ship over 1600 tons to have a Radio Operator on board. The easiest way for a shipping line was to have the Marconi International Marine Company supply all.

Looking at this typical Marconi radio room:

From the left  at bench level - Marconi Atalanta main receiver, next must be his second receiver, another Atalanta receiver (lucky guy).

Then there is the Auto Alarm and (behind his head) the Automatic Keying Device, then the Oceanspan main transmitter.

Above the ship’s call-sign board is the emergency battery charger and 24 volt power management unit. Behind the battery management unit you can just see the Auto Alarm bell. Then there is what looks like a loudspeaker unit which is the front of the Emergency 500kHz only transmitter. Above that is the Aerial Distribution Unit. The Main and Emergency Aerials could be switched between the Main and Emergency transmitters.

The Emergency Lifeboat Transmitter

All ships needed to have a transmitter which could be deployed to a lifeboat. To the left is a photo of the type that I travelled with on all but my newer ships. This thing is about the size of a small dustbin, about 16” diameter and 3’ tall. It had two handles on the top to allow it to be manhandled, the top was sealed with a waterproof dome (shown on the right on the photo) and powered by the pedals.

It transmitted on 500kHz and 8364kHz (though I am not aware that anyone monitored that frequency, it was just in the middle of the 8MHz band and might have been heard by a coast station). It had a Morse key and some aerial matching knobs. It was all valve technology.

Well, after you had recovered from the hernia of getting it into the lifeboat and survived the drop into the oggin your problems started. There was a wire aerial which had to be tied on to an oar and had to be held aloft by one poor soul. The radio operator had to clamp the barrel of the thing between his knees and be stable enough to send Morse code.Two other poor souls had to pedal the damned thing! Being valves, it had to be pedalled for at least 40 seconds for the valves to warm up, then the poor operator could start sending his distress signal. If the pedallers slowed down or stopped the whole process had to be started again. I only tried it once, during a lifeboat practice somewhere up a massive river in the Borneo jungle. God help anyone who really needed to use it!

Thankfully, some time in the very late 1960s this cumbersome thing was replaced by a transistorised version which could easily be strapped to the operators knees and hand-cranked by one person. Not forgetting the poor sod who had to hold the oar (aerial support) aloft.

Direction Finding (DF)

Direction Finding equipment consists of two parts. The specialised antenna system and the instrument on the bridge of a ship that makes use of the signals that the antenna gathers. Below left we have a typical ‘cross-hoop’ antenna usually known as a Bellini-Tosi Loop.

The Wikipedia entry for Bellini-Tosi Loop principles can be found HERE

Basically, looking at the right hand picture above - the Bellin-Tosi Loop picks up signals from the ether (outside the ship), those signals travel down the wires to the windings (F) of the Goniometer. The fields from those coils replicates what the aerials found in the outside world. In the middle of the Goniometer is a coil (S) whose signal is fed to a radio receiver. As the coil (S) in the Goniometer is rotated the signal strength of the received DF Beacon will rise and fall. As a ‘null’ (reduction on signal strength) is easier to find, the Goniometer is rotated for  null. The direction (in Compass degrees) is displayed in the front of the DF equipment (pictured below).

This null will occur at relative bearings of 0 degrees and 180 degrees. A separate receive aerial, called the ‘Sense’ aerial’s signal is added to the equation to work out which is the bearing of the DF Beacon.