WIRELESS TELEGRAPHY FOR MARINE INTER-COMMUNICATION

ANNOTATIONS
Copyright © 2004, Parks Stephenson

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References to Olympic refer to her 1911 configuration. Her post-1913 configuration will not be discussed here.

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1 1/2 KW. MARCONI SET.—Both Olympic and Titanic were originally scheduled to receive the standard 1 1/2-kw apparatus. Because of that schedule, the special number of "The Shipbuilder," published in the Spring of 1911 to promote these ships to the shipping community, included extracts from this "Electrician" article. However, just days prior to Olympic's departure on her maiden voyage, the new 5-kw apparatus was made available and installed on board in a hastily-modified Silent Room. Titanic, several months in construction behind Olympic, had the luxury of having her wireless spaces laid out specifically for the 5-kw apparatus.

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70 TO 300 NAUTICAL MILES.—Olympic's range was officially listed at 350 NM. Titanic's range was listed at almost double that (650 NM), thanks in large part to the additional range that the musical note of the rotary spark apparatus enjoyed over that of the rough spark produced by the plain spark apparatus.

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300 AND 600 METRES.—Often referred to as the "short" and "long" wave, respectively. The short wave was not often used; in fact, there is no evidence to suggest that Titanic ever transmitted on the short wave, except possibly during her initial check-out. Operating the short wave required the condensers and transformer to be configured in series, the spark gap widened, and an extra condenser inserted into the transmitting circuit, through a second earth arrestor. This was done to match the transmitting wave with the natural frequency of the long aerial.

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ROTARY CONVERTER.—The rotary converter was similar in construction to a shunt-wound direct-current motor, but had in addition tappings off the armature, connected to two slip rings on the end of the armature shaft opposite the commutator. Brushes connected to the primary circuit joined across the two rings picked up the alternating character of the current. The strength of the current in a 5-kw apparatus made the rotary converter impractical, so a motor-generator set was instead employed to provide for a safe, physical separation of the D.C. and A.C. windings. A motor-generator consisted of a motor and an alternating current dynamo (as known as an "alternator") coupled together on a common bedplate. The 5-kw motor-generator supplied A.C. power at a frequency of 70 cycles and 300 volts.

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FIELD REGULATOR.—The 5-kw set with a motor-generator required the use of two regulators, one to control the motor field; the other, the revolving field inside the alternator.

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MAGNETIC RELAY KEY.—In the 1 1/2-kw apparatus, a single magnetic key was used to reduce the power, and therefore the erosive effects, of the spark that formed between the platinum contacts of the manipulating key. Because the current delivered from the 5 kw motor-generator was around 100 to 300 volts, an additional coil was inserted into the circuit to bring the voltage in the primary circuit down to a lower level to protect the operator from inadvertently coming into contact with the higher voltage. The double-magnetic relay key was used in the 5-kw transmitting apparatus to both allow the operator to work the manipulating key at a lower voltage and keep the key contacts from fouling.

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SPARK DISCHARGER.—Olympic used a plain spark discharger similar to the type shown in the article. Titanic was fitted with a synchronous (i.e., the rate of sparking was equal to twice the frequency) rotary type discharger, which was essentially a metal disc studded with discharge electrodes that was keyed and mounted on the shaft of the alternator. The disc spun past two stationary electrodes that were connected in series with the closed oscillation circuit. Spark discharges at the disc happened so regularly and frequently that a high-pitched musical note was produced. The note emitted from a rotary discharger was easily distinguishable from the "Shhhh" sound emitted by a plain spark discharger. This was nowhere more evident than on the night of the disaster.

Titanic's rotary spark was, like the plain spark discharger, contained within a lead- and asbestos-lined teak box. The lid of this box was normally kept closed, in order to muffle the noise of the spark discharges and to contain the gases that resulted from same. The spacing of the two stationary electrodes was adjusted by turning a circular ebonite knob on the side of the discharger box.

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CONDENSER.—Olympic and Titanic utilised double-plate, whole-plate condensers in order to deliver the capacity needed to generate the 5-kilowatt spark. Each of the four galvanised tanks contained a bank of whole plates, each with twice the surface area of the half-plates mentioned in the article. There were 36 glass plates, interleaved with 17 zinc sheets (two glass plates between each pair of zincs, hence the name, "double plate"), hung from a cradle inside each tank. A commutator, or controlling device, sat atop the condensers on a wooden framework, which allowed the operator to configure the condensers in parallel (for the long wave), or serial (short wave). The commutator pin arrangement discovered in the wreck of Titanic showed that she was operating the long wave when she foundered.

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ROOF OF THE CABIN.—The Bradfield insulator was affixed directly to the roof over Olympic's Silent Room. This put the insulator on the port side of the Officers' Quarters deckhouse. In Titanic, the insulator was elevated on an approximately 6-foot-high wooden trunk, square in cross-section and located farther inboard and aft of where Olympic's could be found. The insulator was raised to keep it clear of a canvas awning that was part of the design for the roof of Titanic's Officers' Quarters but never utilised during the ship's short career. The brass rod that formed the core of the insulator ran through the entire height of the trunk, and was therefore of extended length. Archival photographs of Titanic reveal the absence of ebonite sparking discs on the visible portion of the insulator shaft; either the discs were located inside the wooden trunk or dispensed with altogether since the trunk would have protected the insulator shaft from spray.

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TWIN T.—Olympic and Titanic utilised the T-shaped aerial. The spreaders were each 20 feet long and there was an 8 foot separation between the two pairs of wires. There are four bands on each spreader, two for each pair.

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CONNECTIONS OF WIRELESS EQUIPMENT.—With a 5-kw apparatus and rotary spark discharger, the schematic below more accurately depicts the configuration of Titanic's transmitting set:

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For more information on Titanic's wireless, read Parks Stephenson's article,
The Marconi Wireless Installation in R.M.S. Titanic