Getting Started in ARDF
de Dale Hunt WB6BYU
It is good to learn to take bearings with your receiver before you go out
on your first hunt. Bearings are directions, in azimuth, from a specific
location. By taking bearings to a particular radio transmitter from multiple
locations, you can get a much better idea about where the transmitter is
located. Taking good bearings is one hte most important fundamental skills
in ARDF. Each receiver is a little bit different, but there are two basic
approaches to taking bearings.
Most two meter receivers will be attached to a multi-element directional
antenna. The most popular antenna designs are yagis, but log periodic
dipole arrays and and phased dipoles are also used. These antennas are
more sensistive in one direction than the others. Holding the antenna in
front of you, rotate yourself, keeping the antenna in the horizontal plane.
When the receiver indicates the strongest signal strength, the antenna
is pointing in the direction to the transmitter. Alternatively, you can
rotate until the receiver indicates the weakest signal strength, in which
case the antenna will be pointing in the opposite direction of the
transmitter. Depending on the equipment you are using, signal strength
may be indicated by a meter on the receiver, by a change in an audio tone
you hear in your headphones, or simply by the received signal getting
The signal strength indicator on a receiver usually only works over
a limited range of signal strengths. If a signal is too weak, the
signal strength indicator may be unable to register anything in any
direction. If the signal is too strong, the signal strength indicator
may indicate its maximum in every direction. For this reason, ARDF
receivers have a receiver gain control that can be adjusted so that
the received signal is in a useful range for the type of indicator used.
Advanced ARDF receivers have automatic gain control circuitry.
Start by listening to the desired signal on your receiver. Make sure
it really is the signal you want to find! Try adjusting the gain
control: the signal should be very weak with the control one direction,
and stronger (possibly much too strong) with the control all the way
the other direction. Adjust the gain control so the received signal
is a comfortable listening level in the receiver. Now turn slowly
in a circle with the antenna. The signal strength should peak in one
direction and be weaker in the other directions. (You may need to
readjust the gain while circling.) It is good practice to stop and turn
all the way around in a circle while you are learning to take bearings
to make sure you are really listening to the strongest peak in the
Most eighty meter receivers will require an entirely different method for
taking bearings. Instead of looking for the strongest signal, you will be
looking for a direction where the received signal is as weak as possible.
Again, tune in the signal and adjust the gain for a comfortable level.
Now turn in a circle: there will be one or two points where the received
signal is much weaker. This is the point you are looking for. The null
can be very sharp, and it takes some practice to find it, especially when
the signal is keyed on and off.
A magnetic loop antenna or a ferrite rod antenna will have two sharp nulls
in the pattern, in opposite directions. We you have found a sharp null
in received signal strength, you know that the transmitter must be in
one of two directions. We must know which of these two directions is
the direction to the transmitter, or we will go in the wrong direction.
Most eighty meter receivers have a small vertical antenna called a "sense
antenna" that is used to change the pattern. When the sense antenna is
active, the antenna pattern will have only one null, and a peak in the
opposite direction. The null (and the peak) are not as sharp as those
without the sense antenna, but some people find they are good enough for
hunting, and they always use the sense antenna. In this case, you can
take a bearing using either the peak or the null, as long as you know
which is which.
The common method of taking bearing uses both patterns. First, find
the null direction using the bi-directional pattern. Then, turn the
receiver sideways and enable the sense antenna (usually, this means
holding down a momentary-contact switch button.) Consider how loud the
received signal is, and then turn the receiver 180 degrees, and notice
whether the signal strength gets much stronger or much weaker. With
the sense antenna enabled, the receiver will be much more sensitive in
one direction than the other (and this direction is usually marked on the
receiver or the magnetic loop antenna.) When the direction of strongest
signal strength matches the direction of greatest receiver sensitivity,
then that is the direction in which the transmitter is located.
Once the correct direction is found, you can walk towards the transmitter
using just the sharp bidirectional null. Because the nulls in the
bi-directional pattern are sharper, you can get more accurate bearings.
The risk you run not using the sense antenna is that you might run right
past the transmitter while it is not transmitting, and not realize that
the transmitter you think is directly in front of you is really directly
behind you. Using the sense antenna once in a while can help you check to
make sure you are still going in the correct direction.