Low
Tech Fox Hunting
by
Don Warkentien, WØDEW
There is lots of information on direction finding and fox hunting using beams, loops and Doppler systems. What is not so easily obtained, is information on how to find a transmitter when you don’t have the special equipment. I feel this is much more important than how to build, buy and use the special equipment.
If
an occasion should arise where it becomes necessary to find a transmitter and
it is not a planned fox hunt, chances are you will not have the special
equipment with you. In this situation
it will probably not be convenient to go home and get it, or by the time you do
go home to get it the situation may no longer exist. Another words when a real need arises where a transmitter must be
located, typically time will be limited.
The
following is referenced to finding a signal on the 2 meter band but you can use
the same process to find a signal on other frequencies.
The
equipment you need for this type of fox hunting is what you have on hand. First is a radio with a signal strength
meter and second is some small wire and a way of cutting the wire and third is
an understanding of how your surroundings may affect a signal.
The
first thing you have to understand is that the signal strength meter does you
no good if the reading is full scale.
When this happens you have no indication how close or how far you are
from the source. The meter must always
be reading on scale. When you get
closer to the signal you must make adjustments to reduce the signal so that it
is on scale. Here are some of the ways
you can accomplish this.
Remove
the antenna and replace it with a short piece of wire of perhaps 1 inch
long. If the signal is still to strong
you can cut the wire shorter and finally just use the radio with no antenna at
all.
If
further reduction is necessary adjust the frequency to one side or the other of
center frequency. If the signal is on
146.500 MHz adjust your radio for 146.505 or 146.495. You can adjust it even farther off frequency if necessary.
When
you start looking for the signal use only enough antenna to get the signal
strength on scale on the meter. Look
around for a large building that you can circle. Walk around the building or drive around the building while
observing the signal strength. You will
find that the signal will be strongest on one side of the building verses other
sides. If you don’t see much change you
may be too far away from the building.
Start driving or walking in that direction while looking for the signal
strength to increase. The signal
strength will bounce around as you move so average the readings you get while
moving.
If
you are in a hilly area and the signal is on the other side of a hill, the
signal strength will be weakest when you are on the side of a hill away
from the source. It will be strongest
when you are on the side of the hill toward the source. The signal at the top of the hill will not
be as strong as the signal on the side of a hill. As you drive be aware also of hills on the side of you that may
affect the signal.
As
you progress the signal should increase to a point and then as you begin to get
farther away it will again decrease.
When you are sure the signal is decreasing go back to the point where it
was strongest. Again determine which
direction the signal is coming from now.
Start traveling in that direction while observing the signal strength on
the meter. At this point you should
have decreased the antenna size substantially to keep the signal on the
meter. You are getting closer and
smaller objects can now block the signal so you can use a metal sign, a truck,
a car or even your body to shield the signal and determine which direction it
is coming from. Large objects are
required to block the signal at a distance while, smaller objects work well as
you get closer.
As
you search you should never have to add more antenna because the signal is
weak. If the signal gets weak to the
point where you can’t hear it anymore go back to a point where you were able to
hear it and go in a different direction.
Never add antenna only remove it when the signal gets strong.
When
you get to a point where the signal is full scale with no antenna and the radio
is 10 kHz off frequency, be careful, you are standing on the transmitter.
73 DE WØDEW