Like other hobbies, transmitter hunting
has its own nomenclature. The following definitions and explanations are
provided to help acquaint the reader with a few of the more common transmitter
hunting terms. These definitions are not intended to cover every context
in which the terms might be used, but simply to describe them in the context
of transmitter hunting.
In this section I have tried to keep the
use of technical jargon to a minimum. However, in the interest of brevity,
I have resorted to using some technical terms. If you are not technically
inclined, don't feel daunted by any jargon you might encounter here. Remember:
you don't need to understand the theory in order to successfully hunt down
hidden transmitters. But, once you've spent some time hunting transmitters,
you may find that you've attained a practical understanding of radio that
makes the theory easier to grasp.
Antennas
An antenna is a metallic device that converts
radio waves striking its surface into electrical signals that can be fed
into a receiver. The cable (or wire) that connects
an antenna to a receiver is known as a feedline, because it feeds the signal
into the receiver. The size, shape, height, design, and orientation of
an antenna determine its operating characteristics, such as directionality
and polarization. Fortunately for most television
viewers, one doesn't need to know anything about antenna theory in order
to successfully use an antenna. But for those interested in the topic,
references [1],
[2]
and [3] are a good place to start learning
about antennas.
Clearly, all transmitter hunting tools
require an antenna of some sort. Many, but not all, utilize a member of
a family of antennas called
beam antennas (or beams). All
members of the beam family share one trait in common: they receive best
in one direction, and less well in all others. This makes using a beam
antenna very simple: just wave the antenna around until you find the direction
that an attached receiver indicates the strongest signal. Barring complicating
factors, such as signal reflections, the transmitter will be found in that
direction.
Beam family members include yagis, quads,
log-periodic dipole arrays, HB9CV antennas, helical antennas, corner reflectors,
horn antennas, parabolic dishes, and many others. Not all beams are suitable
for on-foot, or mobile, transmitter hunting. Some of the more practical
and effective beams for transmitter hunting are described on this web site.
Attenuators
An attenuator diminishes (attenuates) the
strength of the received signal. Why use an attenuator? As you near a transmitter,
its signal strength will increase until it eventually maxes-out your receiver's
S-meter, and provides your receiver with a strong static-free signal. Placing
an attenuator in the feedline between your antenna and receiver will knock
the signal strength down sufficiently so that your S-meter, or the noise
on the received signal, can be used to observe signal strength variations
as you proceed with the hunt.
Attenuators can be divided into two broad
categories:
Active Attenuators
Active attenuators make use of active
components and thus require a source of power (e.g., a battery) in order
to function. The offset attenuator is an example of an active attenuator.
Passive Attenuators
Passive attenuators contain no active
components, but inherently impose an absorptive or reflective loss directly
to any signal passing through them. The resistor network attenuator
(or resistor step attenuator), and the waveguide attenuator (see
reference [3]), are examples of passive attenuators.
See Tactics for
Strong Signals for more information on attenuators.
Fox
The Fox is the individual responsible for
hiding the transmitters. Because the Fox is
in control of the transmitters, he (or she) is the only person who may
be required to possess a radio operator's license.
Hound
The Hounds are the individuals who pursue
the transmitters hidden by the Fox.
Because the Hounds do not transmit (they only receive) they are not required
to possess a radio operator's license.
Polarization
Radio waves leaving an antenna have a property
called polarization. Most of the antennas used in transmitter hunting
emit radio waves that are linearly polarized. Antennas that emit
linearly polarized radio waves will receive linearly polarized radio waves
most efficiently when both the transmitting and receiving antennas are
oriented the same way. Simply put, it is usually to your advantage to orient
your receiving antenna so that it matches the orientation of the transmitting
antenna. For example: if the transmitting antenna is oriented so that the
transmitted signal is horizontally polarized, then you will usually get
more reliable bearings if your receiving antenna is also oriented for horizontally
polarized signals.
If you are not told how the transmitting
antenna is oriented, you may have to experiment to discover how to orient
your receiving antenna for the most consistent and unambiguous bearing
measurements.
If you are not sure how to orient your
receiving antenna for horizontally or vertically polarized radio waves,
then I would recommend spending a few moments researching the topic in
reference [1],
[2]
or [3], or asking a friendly fellow transmitter
hunter.
Receivers
A radio receiver converts the electrical
signals, arriving from the antenna, into sound waves and meter movements
that you can hear and see. Many transmitter hunting tools require an external
radio receiver to make them work. Others come with their own built-in receiver.
For most on-foot hunting with a quad or
yagi antenna, you won't need a fancy
receiver. Any handheld radio capable of receiving FM signals on the
2-meter amateur band, and providing an indication of signal strength, will
be perfectly adequate. In fact, you can use the noise (or quieting) you
hear coming from the receiver as an audible indication of signal strength.
Which means virtually any handheld programmable scanner
capable of covering 144 MHz to 148 MHz should work just fine.
Rules
Because of the wide range of crafty transmitter
hiding possibilities available to the Fox, and the need
to keep the level of difficulty commensurate with a hunt's time limits,
strict rules are often imposed on transmitter
placement and operation. Transmitter hunt rules bear consideration because
they can have an impact on the hunting equipment you choose.
Within the United States, transmitter hunt
rules range from minimal
to elaborate.
Rules here generally are derived from tradition (or from imagination),
and are imposed at the discretion (or whim) of the individual hunt organizers.
As a result, there are no common rules by which inter-regional competitions
can be held. Nevertheless, the freewheeling nature of U.S. transmitter
hunts makes for a diverse and dynamic mix of hunters, hunt equipment, and
hunt methods. It is a good idea to consult with local hunters and hunt
organizers to help you determine the appropriate choice of transmitter
hunting equipment.
Internationally, the situation is quite
different. The International
Amateur Radio Union is recognized as the body with the authority to
establish the rules by which transmitter hunts are conducted, and by which
championship competitions are sanctioned. The sport, known as Amateur Radio
Direction Finding (ARDF),
is defined by explicit
rules, and is conducted in a similar manner worldwide. Regional and
world championships are held on a regular basis. The rules give hunters
a great deal a latitude in their choice of hunt equipment. However, because
ARDF hunts are entirely on foot, size and weight are of paramount importance
when choosing hunting equipment.
Transmitters
The transmitter is the device that generates
a signal for all the hunters to seek. Most transmitters are capable of
operating over a range of frequencies (called a band), and can impart
information on the emitted signal (a process called modulation) using one
or more techniques. In the United States, most recreational transmitter
hunts are conducted using transmitters that operate on the 2-meter band
(144 MHz to 148 MHz), and use frequency modulation (FM). In much of the
rest of the world, hunts are likely to use transmitters that operate within
the 2-meter band (144 MHz to 146 MHz) or the 80-meter band (3.5 MHz
to 3.7 MHz), and use either amplitude modulation (AM) or modulation imparted
by turning the signal off-and-on in the pattern of the International Morse
code (also called CW modulation). The output power of most transmitters
used for recreational transmitter hunts is in the range of a few milliwatts
(0.001 Watts) to 5 Watts.
Surprisingly, finding the transmitter is
not the objective of most transmitter hunts. What the hunters are actually
searching for is the antenna connected to a transmitter. The reason
for this is that the majority of a transmitter's signal radiates from the
antenna to which it is attached, not from the transmitter itself. This
technicality is somewhat academic since a transmitter and its antenna are
usually located close together. But the point is worth noting because sometimes
the transmitting antenna may be attached to the transmitter by a lengthy
feedline, which can lead to confusion. Having identified the antenna, overenthusiastic
hunters have been known to yank the feedline completely out of its connector,
in an attempt to identify the ultimate source of the signal!
A single transmitter hunt might involve
one or multiple transmitters. Transmitters might be on one frequency, multiple
frequencies, or even on different bands. They might be on the air continuously,
periodically, or at random intervals. Transmitters might be carefully timed
so as to prevent more than one transmitter from being on the air at the
same time. Or, they could be timed so as to ensure that two or more
transmitters are always on the air at the same time. Transmitters, and
their antennas, may be clearly identified with a brightly colored marker,
or they could be carefully camouflaged or disguised. Transmitters may be
stationary, or attached to a moving automobile, boat, or aircraft. A transmitter's
power level, modulation characteristics, and its antenna's orientation
might also vary during the course of a hunt. Because of all the ways that
transmitters can be made difficult to find, a set of rules
is usually imposed on the Fox. |