To understand how RF direction finders work, it helps to
understand how radio works. At its most basic fundamental element, electricity
has to do with currents. AC (alternating current) and DC (direct current)
currents that flow back and forth, measured in cycles per second, or more
commonly known as Hz. Radio waves are measured in kHz, MHz and GHz. What radio
is essentially is when the back and forth goes so fast that it jumps off the
wire. The lower the frequency of the current, the longer the radio wave is, and
inversely, the higher the frequency the shorter the wave. When the radio waves
leave the wire, certain antennas can mold how they leave. Similarly, receiving
antennas are custom made to receive certain frequencies and interpret them.
An RF direction finder is made to receive radio
transmissions and determine the direction of the transmitter from data received
by the antennae. These can be modified to many different radio frequency
bandwidths and is applicable in land, sea and air situations. This can be
incorporated for homeland security, aeronautical and marine navigation, the
military, RF tagging systems such as animal tracking, and as beacon homing
devices for search and rescue operations, and other emergency services. Some of
the older RF direction finders date back to WWII, and were used primarily to
locate enemies.
RF direction finding works in two processes: 1) Receiving
and characterizing the signal, by determining the signal strength (closer is
going to be stronger), the direction the signal came from, and the time of
arrival. 2) Processing the data, and based on the information received,
calculate the location of the signal
There do exist radio direction finding (RDF) networks, which
as you can imagine, make signal finding much easier and more accurate than
having just one finder. There are many benefits to having system-level locating
abilities and centralized processing, and having all of the networks processing
together from multiple receiving sites. An example of this is the Coast Guard
Rescue network (the upgraded National Response and Distress System), which
monitors the emergency channels for the marines, and locates distress calls so
that response teams can locate the distress site.
