Two-Way Radio Repeaters: How to Choose and Install
A two-way radio repeater takes weak and
low-performing signals and retransmits them at a higher power so they
can cover longer distances, ranges, and terrains without
degradation. Repeaters eliminate unwanted noise and interference,
helping to clarify messages as they are strengthened and re-transmitted.
When properly installed, radio repeaters provide reliable communication
signals from one radio to another, almost completely eliminating dead
By definition, a repeater is both a radio
receiver and a radio transmitter, a device that receives an analog or
digital signal and amplifies and transmits it further than it would
otherwise be able to go. Repeaters are commonly used by emergency
responders, commercial organizations and amateur radio operators (know
as HAM radio operators) to extend frequency ranges from one receiver to
another. The most basic repeater consists of a receiver
on one frequency and a transmitter on another frequency, usually in the
same radio band (i.e. UHF or VHF), as well as one or more antennas. They
may also require amplifiers, isolators and other accessories.
A Brief History on Radio Repeaters
Military communication units have been using
radio repeaters for many years to allow command posts to transmit both
encrypted voice and data signals across hundreds of miles, while
allowing for a forward moving regime. It was this type of technology
that inspired the radio repeaters on the market today, which are far
smaller, more durable and less expensive.
Military radio repeaters require vehicles to
haul bulky and heavy equipment and provide a heavy-duty power source.
They involve the installation of very tall antennas constructed by
entire communication teams. Using a 50-ft. antenna, military radios can
carry a signal for a maximum of 35 miles. At least a dozen repeater
sites would be required to carry a message 500 miles.
Modern radio repeaters, on the contrary, are
compact, user friendly, and easy to install. Many of them are smaller
than a briefcase, weighing just a couple of pounds. Tough-to-cover areas
are no longer a problem with a radio repeater because range and coverage
limitations are eliminated. Some repeaters promise coverage for a
hundred miles or more with the proper installation.
Types of Radio Repeaters
There are different types of radio repeaters,
each designed for specific uses and situations. Repeaters strengthen and
sustain both UHF (Ultra High Frequency) and VHF (Very High Frequency)
signals, especially in rugged terrain and over water. Most repeaters
available for businesses today use UHF frequencies.
A repeater uses two frequencies, a transmit freq
and a receive freq. It receives signals on one frequency and
re-broadcasts them on another frequency. For a two-way radio to work
with a repeater, it requires a radio that enables the programming of
separate transmit and receive frequencies that match the repeater.
Low-power repeaters are used for onsite
communications, with antennas placed at a low level. These are generally
used for areas as large as a small town or for a campus or building.
These systems may only have 2 to 5 watts of transmitting power.
High-power repeaters are placed atop tall towers
or hilltops to maximize coverage areas. These systems allow users with
low-powered, two-way radios to communicate with each other across many
miles. These systems may contain as much as 100 watts of transmitting
In a digital communication system, a repeater takes a transmitted
regenerates it and sends it along to the next receiver station. A series
of repeater sites make the extension of a signal over an incredibly long
distance a possibility. Digital repeaters are able to eliminate the
unwanted signal, a digital signal, even if it is faint or unclear, can be
completely restored. Analog signals, however, are strengthened with
amplifiers, which, unfortunately, often amplify noise as well as the
communications systems, a repeater consists of a radio receiver, a
transmitter, an amplifier, one or two antennas, and an isolator. The
transmitter produces a signal on a different frequency than the received
signal. This is called a offset, which is required to prevent the transmitted signal from
disabling the receiver.
For more complex installations, an isolator in line with the antenna
cable provides additional protection. An isolator is a one-way band-pass
filter that reduces the ease of signals from nearby transmitters going
up the antenna line and into the base station transmitter. This prevents
the unwanted mixing of signals inside the base station transmitter which
can generate interference. An isolator also reduces the transmission of
undesired signals. Isolator circuitry may be built right into the lower
A repeater, when strategically located on top of a high building or a
mountain, can greatly enhance the performance of a wireless network by
allowing communications over distances that would otherwise be
impossible to cover.
Some organizations now use all digital systems. Unlike analog
signals, digital signals need to be more frequently repeated. Because
digital signals scatter more quickly than analog signals, amplifiers are
often needed. While analog repeaters are spaced at about 18,000 meter
intervals, digital repeaters are usually placed in 3,000 to 6,000 meter
Installing a Radio Repeater
Installation of two-way radios can range from
somewhat complex to incredibly easy, depending on the
configuration. High-power repeaters usually require two antennas, one
for receiving and one for transmitting. Installation of this type of
repeater is complicated and not recommended for the average, untrained
user. The typical repeater for shorter distances, however, requires only
one repeater antenna, which transmits and receives to two-way radios,
usually hand-held devices. These are relatively simple.
In two antenna installations, placement of the
antennas is critical to prevent the receiving antenna from taking in
energy from the transmitting antenna. The antennas are placed at
different heights to minimize this interference.
To make installation easier, some repeaters have
what's called a built-in or add-on duplexer that allows the unit to
transmit and receive on the same antenna at the same time. Essentially,
the duplexer contains circuits that isolate the transmitter from the
receiver. This way, the transmitter’s radio frequency doesn't damage the
Regardless of the use of one or two antennas, a
high-performance antenna is usually positioned at the coverage area’s
tallest point with the repeater. When strategically located at the most
elevated point of a communication site, height greatly enhances the
overall operation and performance of a repeater’s signals. Antennas are
preferably mounted with line-of-sight to all repeaters or other two-way
Before installing a repeater, a site survey and
radio coverage test are vital to its proper performance. This type of
testing and level of planning becomes helpful as it saves time, money
and resources. Investing in these recommended practices on the front end
can essentially eliminate poor equipment performance and ineffective
communication later, and possibly when it matters most.
Repeater Site Survey
Conducting a radio coverage site survey and
finding the right installation location is one of the most important
steps in setting up a radio repeater. Positioning of the antenna is
critical to the overall success of the radio communication that is
depending on the repeater. Finding a prime spot is essential.
Choosing a place for a repeater should be
relatively easy. Line of sight is very important in radio communication.
Trees, electrical towers, hillsides and other dense structures or
objects can impede signal transmission. That's not to say you must
have line of sight. Just know that if you don't your range will be
Once a general area for the repeater has been
identified, several options should be considered as potential antenna
locations. This allows for revision to any plan negatively affected by
unforeseen obstacles that might ultimately hinder signal performance.
Keep these criteria in mind when selecting the
site for your repeater antenna:
- The antenna should be as centered as much as possible
within the coverage area so the strength of the signal is at the same
level as, and able to transmit to, all points within the configuration.
- If you must install the repeater inside of a building,
rather than on top of it, which is ideal, try to look for a height that
is also vertically centered on the area you wish to cover. This reduces
the distance the radio signal must travel by about half. If attempting
to cover a high rise building with 16 floors or more, go to a location
half way up –the seventh floor, for example.
- To ensure safety, be sure the repeater device and antenna
always maintain the minimum distance recommended by the manufacturer
from people and objects.
- If you are planning to permanently install a repeater, be
sure to reference environmental and electrical requirements to ensure
your repeater meets state and federal standards.
- If you are planning to use the repeater to cover a large
area with many buildings, it is highly recommended that you use a larger
antenna. Try to install the repeater antenna at the highest point to
allow as much line of sight as possible.
- Every site is different. Concrete walls, fire panels and
other construction elements can block the penetration of radio signals.
This is also true of other obstructions and these things should all be
considered when conducting the survey and subsequent installation.
- Gradually lower and raise the height of the antenna during
the site survey to see if coverage improves.
- Expect coverage to be somewhat enhanced when the repeater
is permanently installed.
Radio Coverage Test
Once a site has been decided upon, conducting an
RF (radio frequency) coverage test is the next logical step in the
repeater installation process. An RF coverage test eliminates the
possibility of settling on a poor installation location and identifies
adverse environmental conditions that might affect the repeater’s
A coverage field test should be conducted at
whatever site is selected as a repeater location. The objective of the
field test is to replicate the quality and coverage of signals
transmitted by the repeater from a given location. This should be
completed before any permanent installations are implemented. It is
always good to try several options to find the best location for an
antenna to ensure maximum performance of the repeated signal.
Following these quick and easy steps for a
standard coverage test:
Go to the planned repeater area with two
people and pair of fully-charged handheld two-way radios. Before the
test, make sure the radios are programmed exactly to the same
specifications –bandwidths, frequencies, codes, etc..
If you’re planning to have an external
antenna installation, you should try to duplicate, as much as
possible, the antenna’s positioning to best replicate the antenna’s
planned height. Typically, the higher the antenna the better, but
this is not always the case. If needed, position a person on a
ladder or raised element to more accurately replicate the height you
intend to mount the antenna. Remember, you may have to try several
heights and/or locations before finding the one that works best.
The antenna (not the repeater) will be in
the center of the desired coverage area. One person should take one
radio and go to the most likely antenna location. This person’s
communication will represent the type of coverage you can expect if
the repeater antenna were installed in that location. If coverage is
inadequate, relocate to a different location and repeat the process
until the desired range and coverage are optimized.
One person should remain at the repeater while the other person
walks around the area intended for radio coverage, covering the
perimeter when possible.
Both parties should be continuously transmitting and receiving while
communicating across the signal. If the quality of communication
between the two-way radios is good, this means the repeater
transmissions will most likely reproduce a strong, quality signal.
It is best to only change one variable at a time during the coverage
test. For example, adjust just the antenna height or only location,
then repeat the survey process and compare results.
Every communication configuration is different,
and therefore, no specific set of instructions applies when it comes to
determining where to locate an antenna for optimal coverage. In general,
however, remember that the antenna acts as a pivot point for all radio
communication operating on a given channel. The antenna must be at the
area’s greatest vantage point, which will reduce potential obstructions
and enhance the distance a radio signal can travel. This allows the
signal to go from any place in the desired coverage area to the antenna.
When evaluating sites where coverage is needed
in multiple buildings, external mounting of the antenna may be required.
If you are planning to use the repeater to cover such an area, a larger
external antenna mounted as high as possible is recommended. This is
usually true when setting up repeaters in office complexes, shopping
centers and law enforcement compounds.
Before considering an external installation of
any antenna, a site survey should be conducted and then a coverage test.
In this instance, one person should be positioned inside a centrally
located building in the desired coverage area the highest possible
elevation. The second person should walk the site, communicating from
inside every building and at all outside areas where radio coverage is
Always remember when handling radio equipment –
safety is paramount. Use caution when installing and operating
To gain a better understanding of how far you can expect two-way
radios to communicate, more information can be found here:
2-way Radio Range