The eLoran system mentioned in the release adds another pulse to the existing burst. This can provide additional user data. This has been tested in the field, and the extra pulse displays on triggered scopes tuned to the particular chain's Group Repetition Interval. Loran-C transmitter chains use very high pulsed power levels, and they are audible just about anywhere on this low frequency.
Also, more modern transmitters are being installed. These are completely solid state, and essentially high-powered strobes for RF instead of light waves. Controlled by atomic clocks, they dump a huge capacitor across a circuit, producing the precisely timed short pulses that make the system work.
Here's the release from the Department of Homeland Security:
February 7, 2008
Contact: (202) 282-8010
STATEMENT FROM DHS PRESS SECRETARY LAURA KEEHHNER ON THE ADOPTION OF NATIONAL BACKUP SYSTEM TO GPS
Today the U.S. Department of Homeland Security will begin implementing an independent national positioning, navigation and timing system that complements the Global Positioning System (GPS) in the event of an outage or disruption in service.
The enhanced Loran, or eLoran, system will be a land-based, independent system and will mitigate any safety, security, or economic effects of a GPS outage or disruption. GPS is a satellite-based system widely used for positioning, navigation, and timing. The eLoran system will be an enhanced and modernized version of Loran-C, long used by mariners and aviators and originally developed for civil marine use in coastal areas.
In addition to providing backup coverage, the signal strength and penetration capability of eLoran will provide support to first responders and other operators in environments that GPS cannot support, such as under heavy foliage, in some underground areas, and in dense high-rise structures. The system will use modernized transmitting stations and an upgraded network.