Intelligent Radio Direction Finding to Help Locate Down Firefighters

Murray Craig

1 This photo shows the line of bearing (LOB) from a single TigerStrike once the radio signal is detected. With multiple systems, the technology can automatically triangulate a signal. (Photo courtesy of Firestorm Emergency Services, Ltd
1 This photo shows the line of bearing (LOB) from a single TigerStrike once the radio signal is detected. With multiple systems, the technology can automatically triangulate a signal. (Photo courtesy of Firestorm Emergency Services, Ltd.)


It is one of the scariest situations you can imagine: Your department is battling a structure fire when a firefighter calls, “Mayday, Mayday, Mayday,” and the radio goes silent.


What happened? Where is he?

Without a second thought, the incident commander (IC) uses the command radio to activate the rescue beacon capability of the lost firefighter’s radio. He then grabs two TigerStrike® systems, positions the system operators, and searches for the unique digital ID “ping” broadcast from the firefighter’s radio. With the radio “ping” located, the IC initiates a rescue operation.

Every second counts.

Firestorm Emergency Services and the TigerStrike 4100 are ready to aid rescue and recovery operators to respond as quickly and accurately as possible.

This scenario is just as likely to occur in the wilderness fighting wildfires as it is fighting a house fire. At a wildfire, the amount of land and terrain covered creates unique difficulties. If the fire changes directions or flares up, teams of firefighters can be cut off from support and unable to be located. Although resources are in place to aid firefighters in this situation, such as air tankers, these resources cannot be used properly if the location of the firefighters is unknown. Without any action required by the firefighters, the TigerStrike can assist in locating their position and enable these additional resources to provide a protective cover until the firefighters can be evacuated.

Although TigerStrike can locate the digital ID ping discussed above, it can also locate a radio when the firefighter is broadcasting. This enables the TigerStrike to be used in virtually any rescue situation.


From the 1940s to the 1990s, radio direction finding (RDF) was widely used by numerous industries from the military to aviation. However, since the introduction of global positioning systems (GPSs), there have been virtually no innovations in the RDF industry until the TigerStrike. For this reason, the majority of systems available are very large and heavy and do not include advanced software.

Since 2003, I have been heavily involved in search and rescue as a member of the Civil Air Patrol and with Emerald Bay Search & Rescue, where I participated in the Columbia Space Shuttle recovery in Nacadochuse, Texas. As I helped execute numerous searches with outdated technology, I thought, “I can make something better than this.” From there, TigerStrike was developed.

Instead of following the common design of previous systems, the TigerStrike removed the “brains” of the system from the hardware and moved them into the artificial-intelligence-based software application. This enabled Firestorm to develop a light, handheld antenna array, which is highly accurate and very rugged.

The TigerStrike is a Firestorm patent-pending technology originally developed for civilian search and rescue (SAR). The TigerStrike family of phased-array antennas is designed for relatively narrow and specific frequency ranges-a separate phased-array boom with antennas is designed for a given radio frequency of interest, providing maximum accuracy.

A team drawing from years of search and rescue, aviation, racing, and military experience developed the TigerStrike.

It weighs 4.6 pounds without the computer, offers accuracy of ~2 degree with a phased array system, and offers intuitive software and simple hardware operation for simplicity.

The TigerStrike can collect data from a GPS-equipped emergency transmitter (i.e., emergency locator beacon) and help locate a radio transmission source (i.e., firefighter’s radio), including device ID if available. The Firestorm network functionality allows Tigerstrike units networked on the same mission to be integrated into the target solution of each device. This network capability also provides integration with the Tigerstrike Command Software at the operations center.

Phased Array

For those familiar with RDF, the Firestorm Emergency Services proprietary antenna design receives the same gain as a 12-foot yagi antenna with a 12-inch antenna array, which increases mobility and ease of use. An internal three-axis compass accurate to 0.1 degree, coupled with the narrow line of bearing generated from the TigerStrike antenna system, provides the operator with an approximately two-degree line of bearing (LOB) in the horizontal plane and five degrees in the vertical plane. This allows the targeting software to determine the potential beacon location with a minimum of readings. Onboard GPS allows map-based vector creation in relation to the Tigerstrike unit’s position.

The phased array is suitable for locating a specific signal quickly and accurately. In a down firefighter scenario, the firefighter’s unique radio frequency would be input into the software and then immediately searched for. Using one system, the LOB would be plotted onto the mapping application. Two systems networked together would triangulate the signal and plot the location on the mapping application.

Time Delay of Arrival (TDOA)

Although the phased array is an active search system requiring the user to manipulate the antenna, the TDOA system is ideal for a passive search. This means that the TDOA can be mounted on a tripod, tower, vehicle, boat, or aircraft and identify a line of bearing to the radio signal without user manipulation. As the antenna is active, it collects data from 360 degrees and uses the same mapping software as the phased array system.

Although the TDOA is very user-friendly and can provide valuable data continuously, it does not necessarily replace the phased array. The main difference between the systems is the level of accuracy: TDOA is approximately five degrees; phased array is approximately two degrees. This is important as a rescue operation is being fine-tuned or a search is conducted at long range where the difference between two and five degrees can grow to 100 meters or more.

However, if you need the situational awareness a TDOA system provides but also need the accuracy of the phased array, this does not mean you have to start from scratch when you need a more refined location. Users can network any of the TigerStrike systems, phased array, or TDOA together to triangulate the source of the radio signal. The more systems networked together and searching for the signal, the more accurate the location plotted on the mapping application.

Command Center

During a large operation, the TigerStrike system operators and the command element might not be colocated. To enable the command element to have situational awareness of what the TigerStrike operators are seeing, Firestorm has developed its Command Center software. This software runs on a tablet or Windows computer.

As common operating picture (COP) systems become more prevalent in the emergency management industry, instead of needing to move between multiple screens, the TigerStrike software can integrate with these applications as a “sensor,” with the TigerStrike results viewed on the single map. Firestorm has proved this in field tests with the Department of Defense.

Ideal Setup

Users employ all TigerStrike geolocation systems in the same basic way. The TigerStrike platform does not include frequency monitoring or scanning. Initiation of all direction finding (DF) operations requires the system operator to identify the frequency of interest. The TigerStrike operator sets operating parameters that include receiver frequency, search movement radius, and range detection limit. Once configured, the TigerStrike operator begins the search for the transmitter direction. The initial step is to determine the general direction of the signal source by scanning 360 degrees while rotating the TigerStrike to change the polarization of the system antennas relative to the ground to obtain the best reception possible by attempting to align TigerStrike antenna polarization with the polarization of the transmitter antennas. The general direction of the transmission is identified when a “ping” is heard and signal strength indication is at or near its highest value.

Once the operator identifies the general direction, the operator begins to DF on the signal. The TigerStrike operator sweeps back and forth between 45 and 90 degrees of the general direction of the transmission until the system calculates the direction of the signal and the computer map display shows a vector and LOB. The map vector is a two-degree fan or cone-like shape. The vector area suggests the transmitter source location is somewhere within the fan shape. The distance or range from the DF position to the transmitter location is an unknown variable at this stage of the DF process.

Unlike loop and doppler antenna systems, the very selective directional phased array antenna has been demonstrated to have approximately two degrees of aperture at two kilometers, or a 20-square-meter area. The TigerStrike system does not depend on operator intervention during the “hunt” phase, reducing the human interpretation error possibility.

The TigerStrike comprises the following elements:

  1. Phased array or TDOA antenna.
  2. High-performance receiver.
  3. State-of-the-art digital signal processing.
  4. Integration to the Windows 7 or 8 operating system.
  5. Automatic or manual artificial-intelligence-based hunting system.
  6. Automatic mapping of recorded results.

The software-controlled high-performance radio delivers the flexibility of 100- to 1,000-MHz capability using interchangeable antenna systems. All modes of transmissions are detectable. The TigerStrike has a -134-decibal-milliwatt sensitivity.

In a rescue operation, speed and accuracy are vital. The TigerStrike system can help departments dramatically decrease the rescue time and the risk to fellow firefighters going into harm’s way to aid one of their own.

MURRAY CRAIG is the founder and chief technology officer for Firestorm Emergency Services, Ltd., based in Seattle, Washington. He has been involved with search and rescue since 1972, where he has focused on communications, aviation, and ground teamwork.

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