Tactical radios originally designed for land forces will help connect
Navy warships with a new mine-hunting system. Even though the mine-hunter
vehicle is submerged, its snorkel mast remains above water, making
it a suitable platform for the radio’s antennae.
Having real-time communications and data links are basic requirements
in the remote mine-hunting system (RMS), said Brad Hines, program
director at Lockheed Martin Naval Electronics and Surveillance Systems.
The company is under contract to build two RMS prototypes, to be
delivered to the U.S. Navy in 2003. The RMS missions are to detect,
classify, locate and identify bottom and moored mines in shallow
and deep waters.
If the program is successful, the Navy will begin installing the
RMS in new Arleigh Burke-class destroyers, beginning in 2005. These
ships will have a dedicated RMS launch and recovery system. The
RMS consists of a 23-foot-long unmanned, semi-submersible mine-hunting
vehicle that tows a so-called variable-depth sensor, equipped with
a variety of sonar, electro-optical and navigation sensors.
Hines said it makes sense for the Navy to adapt existing radios
for the RMS, instead of developing a system from scratch. “I
think it’s logical to take equipment that’s been proven
in the military, do slight modifications and come up with something
brand new,” he said. “It saves money.”
The data link for the RMS will be integrated into the ship’s
radio room. It will have both a line-of-sight and an over-the-horizon
capability. The controller’s status information for the RMS
vehicle and the variable depth sonar is transmitted over these radios,
as well as the data collected by the obstacle avoidance cameras
and the sonar sensors.
The line-of-sight radio, with a range of 12-15 nautical miles,
is a high-data rate system (3.15 megabits per second) that controls
the status of both the RMS vehicle and the towed sensor. The radio
is an ultra-high frequency AN/VRC-99B, made by BAE Systems. It operates
in the 1.7-2.0 GHz frequency spectrum.
The over-the-horizon radio is a very high frequency (VHF) AN/PRC-117F,
made by Harris RF Communications. Operating in a lower frequency
(30-40 MHz), the 117F can transmit data at 45 kilobits per second.
Its precise range is classified. “We are talking about tens
of miles,” said Hines.
A high-power amplifier enables the VHF signal to perform “surface
wave propagation,” in order to extend the line of sight beyond
the horizon, said Hines. VHF radios typically only operate within
the line of sight.
The signal propagation is caused by a “ducting effect along
the water,” said Joseph Sternowski, director of government
programs at Harris. He explained that the radio wave is bent along
the surface of the water to reach beyond the line of sight.
Even though the 117F is a land-based tactical radio, it suits the
needs of the RMS system, because the antenna is above water, mounted
on the vehicle’s snorkel mast. If the system were completely
submerged, it would not work. Harris engineers modified the radio
slightly, in order to make it operate with the high-power amplifier,
which was specially designed for the RMS.