Nuts & Volts - September 2004

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 Reference 6).

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).