Photo: HDW

VLF/LF Loop Antenna System Submarine Communications VLF/LF Loop Antenna System Submarine Communications

The ability of very low and low frequency transmissions to penetrate seawater allows a fully submerged submarine to copy strategic and tactical communications. For that reason, VLF/LF communication has been used as prime submarine broadcast for many decades. The most common antenna type used for receiving VLF/LF transmissions is the crossed-loop antenna. Although more advanced VLF/LF receiving antennas, such as buoyant wires, are available today, virtually all submarines Photo: HDW in service are equipped with a crossed loop antenna. The VLF/LF Antenna/ Preamplifi er, is designed Lockheed Martin has long many submarines worldwide. We also to mount atop or within been the leader in the fi eld of loop offer the capability of providing custom the fi n of the submarine. antenna systems, having designed VLF/LF receiving antennas for maritime, and manufactured many of the loop air and ground applications, and to fi t the antennas in service today. We offer a specifi c performance and/or installation standard, high quality submarine loop mounting requirements of our antenna system that is in service on customers.

All of the VLF/LF loop antenna systems provided by Lockheed Martin are comprised of fi ve units —

Unit 1 amplifi ers which are housed in an Unit 2 The VLF/LF Antenna/Preamplifi er, is electronics cavity located at the center The Outboard Transmission Line, is designed to mount atop or within the fi n of the antenna. The crossed loop antenna a shielded, waterblocked cable that of the submarine. It can be provided with is in the shape of a picture frame carries the RF signals from the outboard or without a fi berglass fairing. The VLF/ and it surrounds the electronics cavity. Antenna/Preamplifi er to the inboard LF Antenna/Preamplifi er is comprised The crossed loop antenna is fully Amplifi er/Combiner. of a ferrite loaded, crossed loop antenna encapsulated for environmental and a matched set of VLF/LF low noise protection while the preamplifi ers Unit 3 preamplifi ers. One loop is oriented in the are accessible through an access port The Hull Penetrator, provides the fore-aft (F/A) direction of the ship and at the top of the watertight electronics electrical connection through the the other in the athwartship (ATH) cavity. The balanced output of each submarine pressure hull. This penetrator direction. The VLF/LF signals receive matched loop preamplifi er is provided is of the M24231 type and is sub-safe patterns on the loop antennas in the form at a single, watertight connector certifi ed. If specifi ed by the customer, of orthogonal fi gure-eights. These signals located at the bottom of the Antenna/ other hull penetrator types can be supplied. are preamplifi ed by matched low noise Preamplifi er Unit. A stuffi ng tube can be used in lieu of a penetrator if the customer so desires. Specifi cations Performance Lockheed Martin Outputs (Two Provided) Balanced, 50 Ohm, Omni-Azimuthal Pattern offers a standard, Frequency Band 10 - 160 kHz (Usable through 1.5 MHz) high quality Omni-Azmuthal Response Better than 1.5 dB from 10 - 160 kHz through 360° of Azimuth submarine loop System Effective Height (Omni) 1.0 Meter Nominal into 50 Ohms antenna system System Effective Height (Bi-Directional) 0.5 Meters Nominal into 50 Ohms that is in service Sensitivity (Omni) Better than 0.26 μV/m/Hz1/2 - 10 - 20 kHz Better than 0.14 μV/m/Hz1/2 - 20 - 160 kHz on many Sensitivity (Bi-Directional) Better than 0.2 μV/m/Hz1/2 - 10 - 20 kHz submarines Better than 0.12 μV/m/Hz1/2 - 20 - 160 kHz worldwide. Output Impedance 50 ohms Nominal Maximum Output 0.1 VRMS Open Circuit for Less Than 1 Percent Total Harmonic Distortion Antenna Loops Ferrite Loaded, Crossed Loops, Oriented Fore-Aft and Athwartships (Displaced by 90° from Each Other) Antenna/Preamplifi er Preamplifi er Two Identical (F/A and ATH) Located Integral without fairing. to the Antenna Antenna Nulls Greater than 40 db Amplifi er/Combiner Input Power 115 VAC, 50/60 Hz, 10 Watts Nominal

The VLF/LF Antenna/Preamplifi er can be provided Antenna/Preamplifi er with or without fi berglass fairing. with fairing.

Unit 4 supplies for both inboard and outboard The Inboard Transmission Line, is use. The preamplifi ed VLF/LF signals the same cable type that is used for the from the Antenna/Preamplifi er arrive outboard Transmission Line. Watertight at the Amplifi er/Combiner input as connectors are not used inboard. orthogonal fi gure-eights. These signals are amplifi ed and distributed to a Unit 5 bi-directional 50 ohm, balanced The Amplifi er/Combiner, is located communication output. They are also in the submarine radio room and combined in an omni pattern generator provides the interface between the to produce the omni-azimuthal signal. unique Antenna/Preamplifi er and Separate output drivers provide this standard shipboard receivers. It omni signal to two, balanced, 50 ohm contains low noise amplifi ers, an output jacks which can be cabled to omni-azimuthal pattern generator, any standard VLF/LF communication output drivers and the required power receiver. ©2006 Lockheed Martin Corporation All Rights Reserved Lockheed Martin MS2 Seven Barnabas Road Marion, MA 02738 An ISO9001:2000 Company Sea-Air Systems 508.748.1160 (x138) e-mail: [email protected]

OCT2006/NDCR/20060006/Covers:2006