What is radio direction finding/radio direction finder?
Radio direction finding is a technology that is used to determine the direction of a radio transmitter such as a beacon or radio transmitter. There are several types of radio direction finders: systems based on signal strength and systems based on phase. Signal strength based systems approach relies on the rotation of the antennas and determining the maximum signal level. A system based on phase typically has indicators that shows the direction of the signal or indicator whether it is to the right or left. The Hammerhead is the only hand held system that utilizes both signal strength and directional indicators (not rigth left indicators). There is no system as advanced or easier to use than the Hammerhead.
Why do I need a radio direction finding equipment?
Although a PLB will transmit a location coordinate to a search and rescue organization such as the Coast Guard, there is no guarantee that the rescue will commence in a timely manner. In a man overboard situation, minutes matter so having a way to locate the man overboard is the only way to guarantee that the man overboard is found immediately.
What are the different types of beacons?
PLBs (Personal Locator Beacons), ELTs (Emergency Locator Transmitter) and EPIRBs (Emergency Position Indicating Radiobeacons) refer to a general class of devices that transmit on 121.5MHz for close range homing (without GPS) and 406MHz with GPS location. The 406MHz signal is picked up by satellites to be relayed to international rescue organizations such as the Coast Guard. These devices are required to be registered before use to prevent misuse and false alarms. They are based on internationally agreed upon standards and are typically compatible with search and rescue systems worldwide.
MSLDs (Maritime Survivor Locating Devices) are also beacons but specifically for maritime use. There are a number of different types of MSLD devices. These MSLD devices typically follow an international standard and do not transmit the 406MHz signal. There are 121.5MHz only beacons used for local homing. VHF DSC are beacons that can transmit a GPS signal (either digitally or voice) to maritime VHF radios. Mobilarm/Sea Marshall has a good "white paper"on this subject. A VHF DSC may need to be configured with a proper "MMSI" (Maritime Mobile Service Identity) ID.
There are other proprietary man overboard products.
What is the best man overboard system to use?
PLBs are useable in and around waterm and also be used on land. Most search and rescue personnel (whether land or maritime) are trained to track the 121.5MHz signal from a beacon. It is also a universal frequency and is supported all around the world. A MSLD VHF DSC beacon is an excellent choice as well for water use given that you have an appropriate receiver. Each type of equipment has its own advantages and disadvantages.
To receive the digital GPS position information from a MSLD VHF DSC beacon a proper VHF marine radio is required. The location information is only transmitted intermittently (typically every five minutes for 30 minutes then every 10 minutes thereafter) but there no guarantee that the transmissions are received correctly everytime so the actual time to get the coordinate may be higher than the transmission rate. On a PLB the 121.5MHz is always on so there is no wait period until the next transmission.
The transmitter power on a MSLD VHF DSC device is much higher than a PLB transmitting 121.5MHz, thus the range of a signal will be much farther than a PLB but it does not transmit the signal to a satellte. A PLB transmit a second high power signal with its GPS location to a satellite, so a PLB coverage is nearly ubiquitous (any where in the world due to satellite reception). In situation where the beacon signal is not picked up locally, it can still be received by a satellite and the proper search and rescue operation be started by the authorities.
Does your system use the doppler technique?
No. The Hanmerhead uses patent pending direction finding technique that is not doppler based. Doppler systems are bulky due to the large antennas and are very sensitive to reflections and signal variations. It is difficult to make a hand holdable doppler system that is small, accurate and reliable. Doppler systems also require that the distance between the antennas are large, typically 12 inches or farther apart and at least three dipole antennas are needed. Finally, typical doppler systems cost significantly more and require fixed mounting to work properly.
Why can't the Hammerhead be used on land?
The Hammerhead is designed for vertically polarized signals, which is pretty much guaranteed if the beacon is on water. That is the antenna should be pointed up in the sky. When a beacon is on land, the antenna may be horizontal to the ground or even pointed upside down. In such situation, the directional indictor may not be valid.
The range can be severely limited due to non line-of-sight operation as hills or other obstacles can absorb the signal. In other cases when the signal is reflected, the direction may indicate the reflected direction not the actual beacon direction.
An advanced/expert user may be able to use the product on land, but due to the complexity and skill involved, the Hammerhead is not sold for direction finding on land.
What is the range of the Hammerhead?
Range will vary depending on the following factors: transmitting power of beacon, height of receiver over water, height of transmitter antenna above water and whether the signal is being blocked. The range over land can be extremely short due to the signal being blocked and the ground absorbingsome of the signal. The direction may not be precise due to the signal being reflected (such as builings or hills). This is expected from any direction finding equipment but can be overcome with proper training. We've tested the Hammerhead with a test beacon at 2 and 3 miles transmitting approximately 100mW. Some PLBs transmit less than 100mw, so the range will be reduced. You can watch the demo video here.