Communication with submarines is difficult because radio waves do not easily travel through salt water. The obvious solution is to surface and raise an antenna above the water, but surfacing makes the submarine visible to enemy ships and hence vulnerable. Another solution is to use a buoy carrying the antenna that is floated to the surface. The buoy is tethered to the submarine which remains well below the surface.
Before long engineers figured out another technique. They discovered that radio waves having very low frequency, in tens of kilohertz and lower, has the ability to penetrate salt water up to several meters. So if the radios on a submarine switched to those frequency they could communicate with the naval base while remaining submerged. The trouble was the size of the antenna required. You see, the wavelength of a radio wave is inversely proportional to its frequency, and the length of the antenna required to transmit and receive such a radio wave is directly proportional to the wavelength. In other words, the lower the frequency of the radio wave, the longer and larger the antenna required.
In the case of very low frequencies, 30 KHz and lower, typically used for submarine communication, even a quarter-sized antenna will be several kilometers long. Obviously, an antenna of such dimensions is physically impossible to build. So engineers use antennas that are only a fraction of the wavelength long. The downside of this is the antenna has to be fed an enormous amount of power, because an antenna that is only a fraction of the wavelength long radiates only a fraction of the power it is fed. It is a trade-off engineers have to make in order to keep the size of the antennas down within practical limits.
The Goliath site overlaid with location of the antennas and the transmitter & control building. Image courtesy: nonstopsystems.com
One of the biggest antennas used for submarine communication, appropriately named Goliath, used to stand near Kalbe an der Milde in Saxony-Anhalt, Germany. It was operated by the Nazis during the war period, and had a transmission power that could be boosted all the way up to 1,000 kilowatts. Transmitting at frequencies between 15 kHz to 25 kHz, the Goliath was able to reach German submarines anywhere in the world even when submerged twenty meters below, except when the submarines were positioned in deep Norwegian fjords. It was the most powerful transmitter of its time.
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Goliath used three umbrella antennas, so called because of the guy wires that radiate from the mast to the ground. These guy wires not only provide support, but are part of the antenna itself. Umbrella antennas are some of the most efficient antennas in the low frequency spectrum. Aside from military communication, these antennas are commonly used in medium-wave and longwave AM broadcasting stations.
The Goliath used three 210-meter-tall steel masts arranged in a triangle and guyed to the ground. The antenna system also had an extensive system of buried ground radials whose total length was at least 350 km. Overall, the complete antenna system had a very impressive efficiency—nearly 50% on 15 kHz, and as much as 90% on 60 kHz.
After the war, the Soviets dismantled Goliath, packed it into crates and shipped it to Russia, where it was erected near Nizhny Novgorod, about 18 km south of Gorky and 50 km east of Moscow. It is still operated to this day by the Russian navy, who use it for communication with submarines and to transmit time signals.
The Goliath transmitter in Nizhny Novgorod. Photo credit: Eugene Katishev/Wikimedia
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