New Life for LORAN — Part 2
The vacuum tube station has three
400 KW diesel generators, which will
immediately start up, parallel
themselves, and operate an automatic
transfer switch (ATS) to provide station
power when utility power is lost. Despite
the fact that under emergency
operation some of the station’s load is
shed (“non-essential” circuits), it still
takes at least two of those generators in
parallel to put George back on air. A
view of the three generators is shown in
Figure 4. The generators can be up to
speed and supplying three phase 460 V
AC in less than 30 seconds. The transmitter can then put itself back on air
about 30 seconds after that, so the total
lost signal time lost is about one minute.
By contrast, the solid-state station
has two physically smaller diesel generators, rated at 400
kW each. When loss of utility is sensed, they both start
up, but only one picks up the load. They do not parallel.
After five minutes, the “loafing” generator shuts itself
down. All load is carried; there are no non-essential
circuits, but the major difference is that the LORAN
signal does not go off air at any point because there is a
240 KW UPS (Uninterruptible Power Supply) that
continues electrical power to the solid-state transmitter.
There’s also an 8 KW UPS that supplies power to the
timing and frequency control equipment shown in Figure
3 of last month’s article. The UPS equipment really
doesn’t power the station for long because the generator
can pick up the load in about 10 seconds. Wow!
The combinations of reliable, solid-state transmitting
equipment, computerized control equipment, and the UPS
equipment will result in LORAN signal continuity of from
99.85% to a target of 99.99% (see Reference 4). The
vacuum tube equipment was achieving signal continuity of
99.70%, on average. The Coast Guard prides itself on
keeping that signal on air and in tolerance for its users as
much as possible.
around in orbit to meet whatever need
there might be. This would leave other
areas on the globe with “holes” of coverage. The GPS signal operates at L band
and, therefore, doesn’t penetrate
buildings or heavy foliage very well. Its
signal is so weak that it can be jammed
(unintentionally) by something as
simple as a poorly maintained active
marine TV antenna (see Reference 5). It
can also be jammed (intentionally) by a
simple, low wattage, portable transmitter
in the hands of the wrong people (see
The LORAN signal can be used as
a backup to GPS because of its robust
signal-to-noise capability and its low
frequency of operation. It does not,
however, have the pinpoint accuracy of
GPS — which can be as good as 10 meters and as poor
as 100 meters. The US Coast Guard lists LORAN’s
accuracy as 0.25 nautical mile (NM) nominally with 0.1
NM at the best of times (see Reference 7). The signal’s
coverage can be from 600 NM to 1,000 NM, depending
upon the time of day and path.
LORAN’s strong suit is that the position displayed is
Figure 5. The crew at LORSTA George
who helped put the new equipment
on air and shut down the legacy
vacuum tube transmitters. Standing
left to right: ET1 Ken McKinley,
ETC Kevin Anderson, ET3 Ross
McDermott, MK1 Richard Boxleitner,
SK1 Sterling Van Horn. Kneeling:
FN Ryan McDermott (no relation).
Photo courtesy of ETC K. Anderson.
The Future of LORAN
Where do we go from here? After spending approximately $100 million — so far — upgrading the vacuum tube
stations to solid-state transmitters, will anyone use the signal? Yes, but probably not in the way LORAN was originally intended to be used.
Without question, the dominant form of electronic navigation around the world is GPS. The units are so small,
inexpensive, and packed with features that a lot of amateurs have them married to a TNC (Terminal Node
Controller) and two meter FM rig for APRS (Automatic
Position Reporting System).
GPS is not infallible, though. Since the system was
built for military purposes, the owner can move satellites
Circle #89 on the Reader Service Card.