The above picture shows the antennas of the Titanic
This started when VA3PCJ asked me a question about the antennas of the Titanic. In true amateur radio operator fashion before I could do the research he did it himself and answered his own question…
.
I then asked if he would share it with us and so here is his response and his article follows…
.
Hi Bob,
Here you go… Feel free to modify it any which way you wish:
73,
Jose VA3PCJ
.
==========
Well I did not modify anything… This is a staight CUT n PASTE from our Guest Blogger VA3PCJ and I thank him for sharing with us today…
.
.
The Marconi 500 KHz antenna in the Titanic had intriguing features. From information gathered from the internet (which is not always completely reliable…) the Titanic antenna was a 1/4 wave, center-fed, “Twin-T” antenna made of parallel wires (bare silicon bronze 7/19 cables – made of 7 wires and 19 strands). Its 150m (1/4 wave from 600m) did not span the entire distance between the two masts in the ship. The wires hung between rubber insulators between the forward mast and a point somewhere between the 3rd and 4th stacks where further insulators joined them to tarred hemp lines stretching them to the other mast at the stern of the ship. The four wires were parallel but sagged differently, with the two outer wires having a more promounced catenary than the inner ones. All four wires were “center-fed” each individually via four separate “lead-in wires” entering the deck at the roof of the “Marconi station” at the top deckbetween the first and second stacks. The feeding points for the central wires were a few feet forward than those of the lateral wires.
.
I was particularly intrigued by the nature of the feed-lines which seems to have been single wires similar to those of the antenna, in which case these wires probably irradiated more than the wires strung nearly horizontally high above. THe only description in the internet pertaining to these wires was found in http://titanic-model.com/marconi/article.shtml: “The four feed lines were grouped together on an insulated lead-in stay which ran to a bullseye and anchor on the radio room roof.This took the stress of the aerial’s movement high overhead.An insulated lead-in from each of the two Twin-Ts tapped off from the stay and entered the pillar about 6 feet above deck.The leads passed through the roof inside the pillar (conduit).”
.
However, no description was found as to how the feed lines were actually connected to the horizontal wires on top or to the transmitter and how the antenna would have actually worked: was the “Twin T” actually a dual “L” with the feed lines being also radiators? Did it require a mirror image from grounding of the negative pole of the transmitter to the hull and seawater? It is difficult to imagine it to have been just a 1/4 wave dipole…. or was it?
.
Any information on this topic would be greatly appreciated.
.
73
Jose VA3PCJ
—————————-
.
If anyone has any additional information please feel free to leave it as a comment to this posting or if you wish you can email it to me and I’ll cut and paste it into an article giving you credit as the Guest Blogger…
Thanks again to VA3PCJ for todays posting…
73bob
Tags: amateur radio, Antennas, RMS Titanic, VA3PCJ
April 10, 2012 at 6:39 pm |
I’ve long bee intrigued by the Titanic story and did a search on the sister ship The Olympic and found a detailed reference of the Titanic’s Aerial:
Titanic was fitted with a Marconi twin “T” type aerial, rising vertically from the roof of the Marconi Silent Room, connecting with four horizontal wires strung between the ship’s two masts. Positive electrical connection was made between each vertical lead-in and its corresponding wire in the horizontal flat top by means of a McIntyre connector. Two 20-foot spreaders at either end of the flat top portion spaced the two inner wires 8 feet apart and the two outer wires 6 feet from the inner wires. The aerial spreaders were supported by bridles of tarred hemp rope (ratline), which in turn could be raised or lowered by rope halyards run through reef blocks attached to the top of their respective masts. The forward spreader had four eyebolts, each of which took an aerial strain insulator, from which an individual aerial wire was run.
The fundamental wave length of the aerial was 325 metres, which provided a good value of aerial current at the 600-metre adjustment and a fair value at the 300-metre wave adjustment. Two reasons dictated the aerial’s physical length: 1) The aerial could not be reduced to less than one-half its physical length; and 2) Titanic’s two masts were stepped approximately 600 feet apart. The length of the horizontal wires was therefore limited to keep the 300-metre radiated wave within limits. This meant that the strain insulators for the after portion of the aerial were suspended over the space between the 3rd and 4th funnels, instead of attached directly to the aft spreader with the remaining wire aft of the insulators serving only as support. Also note that the lead-ins had to be taken from the exact centre of the flat top; otherwise, each branch of the “T” would have a different wavelength, making accurate tuning impossible.
A Bradfield type Deck Insulator, rated for the 5-kW marine generator set and able to withstand a minimum of 30,000 volts, was used to insulate the aerial from the steel structure of the ship. The insulator was elevated on an approximately 6-foot-high wooden trunk, square in cross-section, to keep it clear of a canvas awning that was part of the design for the roof of the Officers’ Quarters but never utilised during the ship’s short career. In order to protect the Bradfield insulator from the strain of the aerial being pulled by the wind, the lead-ins were firmly attached to a screw eye in the roof of the Officers’ Quarters and electrically isolated by a single strop insulator. Electromagnetic energy was transferred between the aerial and the Bradfield insulator by way of two flexible wires that ran from the terminus of the lead-in wires to the insulator’s shackle head. The brass terminal socket on the lower end of the insulator rod inside the Silent Room secured the wire connection to the Aerial Tuning Inductance as well as to the two plug sockets mounted on the aft bulkhead of the Marconi Room. The plug sockets were located within easy reach of the operator so that he could switch the aerial from the earth arrester to the induction coil in the emergency set.
Bob VE3MPG
April 10, 2012 at 6:39 pm |
Here’s the link to the above info:
http://marconigraph.com/titanic/wireless/mgy_wireless.html
April 11, 2012 at 2:06 pm |
Hi Bob VE3MPG,
Thank you very much for the info on the Titanic antenna that you
provided.
According to that information, and contrary to information found
elsewhere in the web, the antenna would have been close to 1/2 wl.
(325m). Yet, this length does not seem to correspond to the physical wire lengths as observed on pictures (~150m for the top wires and perhaps another 1/8 wl for the feed lines). Would the capacitor structure provided by the horizontal wires account for this? I am sure that my doubts are due to the fact that I do not understand how the wires were actually connected. If all 4 feed line wires shared the same polarity then they would have been a radiating part of the antenna. Could you cast some light on what exactly is (was?) a “McIntyre connector”?
Much appreciated.
73,
de Jose VA3PCJ.
May 14, 2012 at 2:04 pm |
[...] Jose wrote a previous article for us which can be found here [...]