CHINO VALLEY FIRE TRAINING DIVISION
Radio Communications
June 2014
Article Five
So What’s The Problem?
Two Basic Types of
Communication Dispatch
Centers
1.
Command Center–
has a Captain or Chief Officer
that may augment or tier responses due to information or inclement weather or special circumstances (aircraft down, high winds,
swiftwater, shooter, etc)
2.
Dispatch Center–
has a the ability to dispatch units
under predesignated run cards or
computer generated zones
Radio Spectrum
Bandwidth/Waves
Interference
Over the past decade, incidents involving firefighter injuries and fatalities
have demonstrated that, despite technological advances in two-way radio
communications, important information is not always adequately communicated on the fireground or the incident scene.
The continued incidence of firefighter fatalities where communications are cited as a contributing factor as well as the industry-wide lack of consensus on
the appropriate frequencies to use in fireground communications have
prompted safety organizations to more thoroughly investigate fire communications and the problems associated with those communications.
In this issue:
What’s The Problem?
One of the most significant problems facing firefighters
within a structure or in the WUI (Wildland Urban Interface)
is the ability to communicate reliably between the firefighters themselves and command staff or dispatch. In an ideal
world, firefighters would be able to communicate with one
another and the command post at all times, regardless of
where they are or what they are doing. However, this is not
the case. Firefighter radio communications to, from and
within structures can be unreliable, thereby compromising
the safety of firefighters on the fireground.
1
3
4
6
Direct/Simplex
7
Repeaters
Radio Usage
9
11
The nature of most firefighters is to dig deep into how things work and why
they fail. In this months review, there are explanations as to how communications work from the technical side of things and to understand radio limits. In
the Chino Valley, depending on location, radio communication issues will always be a challenge. Knowing radio limitations within first-in districts is an important pre-planning exercise that should be done with firefighting crews before an actual incident. The most important information for crews to obtain is
the proper channels and repeater tones (if using VHF).
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communications
June 2014
Article Five
Technical vs. Discipline
Communication problems commonly encountered by firefighters can be
A few Radio Tips:
***To avoid noise into
the microphone of your
radio during high winds,
face toward the wind and
speak into the Mic. The
radio will shield your
voice as you communicate. Turning your back
toward the wind allows
those air currents to
transmit along with your
communication making
transmissions unreadable
***The optimal position
for portable radio transmission is at head height
with the antenna in a
vertical position. Not
exactly the position you
may find yourself when
involved in fire combat
operations.
broadly divided into two categories. First are mechanical or technical issues
related to unsuitable equipment, system design, inadequate system capacity
(too much radio traffic), and building construction, among others. The Second
category of problems relates to human factors.
Fire departments consistently have problems maintaining effective communications while operating in large structures, such as high-rise office buildings
and apartments, and warehouses. Similar issues exist in structures with a
large number of windows (or areas of glass) with reflective coatings such as
areas in Chino Hills. Communications from areas below grade (e.g., basements, parking garages, topography) tend to be uneven. For the residential
structures, communications are generally not a problem. The technical issues
associated with the physical structures themselves (building materials, height,
etc.) are discussed further in the pages of this article. Solutions currently used
by Chino Valley Fire range from increasing the number of future repeaters to
experimenting with trunked communications systems.
Human factors, such as radio discipline, training,
and tactical decision making, also affect firefighter
radio communications. In recent training sessions,
discussion of keeping radio traffic to a minimum and
allowing First-In Officers to initiate a plan without pressure of incoming units
would benefit fire operations. These factors, while not technical issues themselves, adversely affect communications, especially when combined with
technical and equipment issues. The bottom line of radio communications is
to continually train with the equipment independently and with crews to know
it’s operation and limitations.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Technology
Radio Spectrum
Radio communications are possible because of electromagnetic waves. There are many types of electromagnetic waves, such as heat, light, and radio energy waves. The difference between these types of waves is
their frequency and their wavelength. The frequency of the wave is its rate of oscillation. One oscillation cycle
per second is called one hertz (Hz). The types of electromagnetic energy can be described by a diagram
showing the types as the frequency of the waves increase.
When describing the frequencies used by common radio systems, we use the metric system to quantify the
magnitude of the frequency. A typical frequency used in fire department radio systems is 154,280,000 Hz.
This is a frequency designated by the FCC as a mutual-aid radio channel. Dividing the frequency by the metric system prefix mega, equal to 1,000,000, this becomes 154.280 megahertz or MHz.
Land mobile radio systems are allowed to operate in portions of the radio spectrum under rules prescribed by
the FCC. These portions of the spectrum are called bands, and land mobile radio systems typically operate
with frequencies in the 30 MHz (VHF low), 150 MHz (VHF high), 450 MHz (UHF), 700 MHz, and 800 MHz
bands.
The wavelength is the distance between two crests of the wave.
The frequency and wavelength are inversely related so that, as
the frequency of the wave increases, the wavelength decreases.
The length of a radio antenna is related to the wavelength with
which the antenna is designed to operate In general, the higher the
frequency of the waves used by the radio, the shorter the antenna
on the radio.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Technology
Channel Bandwidth
The radio spectrum is divided into channels. Each radio channel is designated by a frequency number that designates the center of the channel, with half of the bandwidth located on each side of the center.
Radio channel bandwidth is the amount of radio spectrum used by the signal transmitted by a radio. The greater the
bandwidth, the more information can be carried by the signal in the channel. Minimum channel bandwidth typically
is limited by the state of technology, and the bandwidth required to carry a given amount of information has decreased by several times over the past 50 years. However, there is a theoretical limit below which the bandwidth
cannot be decreased. In addition, the actual width of a channel often is slightly greater than the minimum width, to
provide some space on each side of the signal for interference protection from adjacent channels. For the purposes
of radio licensing, the FCC sets the maximum and minimum bandwidth for channels in each frequency band.
The bandwidth of channels typically used in land mobile radio is measured in thousands of hertz, or kilohertz, abbreviated kHz. In an effort to place more communications activity within a limited radio spectrum, permitted bandwidth has been decreasing. Under older licensing rules, some of which are still in effect, typical channel bandwidths
were 25 kHz. Newer rules require bandwidths of 12.5 kHz.
Radio Wave Propagation
To send a radio signal from a transmitter to a receiver, the transmitter generates electromagnetic energy and sends
that energy through a transmission line to an antenna. The antenna converts the energy into electromagnetic radio
waves that travel at the speed of light outward from the antenna. If another antenna is located in the path of the
waves, it can convert the waves back into energy and send that energy through a transmission line to a receiver.
Radio signals emitted from an antenna
travel both a direct path to the receiving
antenna, and a path reflected from the
ground or other obstacles. This reflection
causes the wave to travel a longer distance
than the direct wave.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Technology
(RADIO PROPAGATION CONTINUED)
The waves traveling over the reflected path then interfere with the direct waves, causing an effect know as
multipath interference. Multipath interference causes a variation in the signal level at the receiver. The signal
may be higher or lower than the direct signal depending on the position of the receiver’s antenna. As the antenna is moved around, the signal varies, and the user hears a signal that goes from strong and clear to weak
and noisy.
Radio waves can travel through some materials, such as glass or thin wood, but the strength is reduced due to
absorption as they travel through. Materials such as metal and earth completely block the waves due to their
composition and density. In addition, some materials will reflect radio waves, effectively blocking the signal to
the other side.
Because buildings are built from many types of materials, the radio waves can be passed through some, be
reflected by some, and be absorbed by others. This, along with the complex interior design of a building, creates a very complex environment for radio communications inside a building.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Technology
(RADIO PROPAGATION CONTINUED)
Interference
Radio frequency interference can be either natural or manmade. Interference from internal
noise occurs naturally in all electronic equipment due to the nature of the electronic circuit
itself. Manufacturers take this into account during equipment design, and obtaining a lownoise design is not particularly difficult. In addition, natural noise is produced by sunspot
activity, cosmic activity, and lightning storms. This noise usually is of small magnitude and
not significant for most land mobile radio communications. However, the VHF low band is
affected significantly by severe sunspot activity, sometimes to the point of completely prohibiting communications.
More significant to radio communications systems is the interference produced by
manmade sources. Vehicle ignitions, electric motors, high-voltage transmission lines, computers, and other equipment with microprocessors also emit radio signals that can interfere
with public safety radios.
In general, manmade interference decreases with an increase in frequency. The UHF band
and, initially, the 800 MHz band are much less susceptible to manmade interference than
the VHF low and high bands. When systems are not subject to significant interference, they
are said to be “noise limited,” in contrast to “interference limited.” The large number of
transmitters used by cellular telephone companies has created intense interference in the
800 MHz band.
Although the separation of the channels allocated to cellular companies has reduced this
interference, communications problems still can occur when a user is operating close to a
cellular transmission facility. This type of interference is particularly a problem when the user is located near a cellular facility and the user’s radio system site is located much further
away. This creates a situation called near-far interference. The user’s system signal
strength is low, and the cellular signal is high, keeping the user’s radio from receiving the
desired signal. The 800 MHz band always was regarded as the “cleanest” band with respect to manmade interference, and systems initially were noise limited. However all systems in the band now must be designed for maximum interference from nearby transmitters, requiring more transmitter locations and higher power creating more costly systems.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Technology
Direct and Repeated Radio Systems
Radios communicate when the transmitter sends out a signal that is received by one or more receiving radios.
When the signal is received from the radio initially transmitting the signal, the communication is direct (i.e.,
there is no intervening radio or system). One radio transmits, the other radios receive, and this type of communications also is known as simplex communication.
Nonsupported Simplex Communications on the Fireground
Using simplex communications maintains positive communications between the IC, exterior onscene units,
and interior units without the reliance on exterior communications systems. Maintaining positive communications is especially important in “Mayday” situations. When users on simplex radios are deployed to the interior
of a structure they create a radio receiver network. As more and more radios move into the structure, the
strength of the network increases. If Engine 1 calls Mayday, the probability of another radio on the interior receiving the transmission is high. If the Mayday is not heard by the IC, another radio operator on the interior can
act as a human repeater to repeat the message to the IC. In addition, the number of radios in a structure creates redundancy, where reliance on a single repeater or trunked system creates a single point of failure.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Technology
Receiver Voters — Improve Field Unit to Dispatcher Communications
Dispatch centers connected to high-powered transmitters provide the dispatch center with
talk-out capability. Transmitters are elevated to achieve better line-of-sight communications
with the service area. High-powered transmitters ensure that the dispatch center transmissions are heard throughout the service area and provide some level of in-building coverage.
Portable radios have limited power and cannot always transmit a signal strong enough to
reach the transmitter sites. To provide a more balanced system, receivers are networked
together throughout the service area in a receiver voter system (RVS). Comparison of the
received audio signal takes place in a receiver voter. The receiver voter and its network of
receivers are referred to as the RVS. The RVS usually is located at the dispatch center.
The receiver voter compares the audio from all receivers and routes the audio from the receiver with the best audio quality to the dispatcher. This type of system provides very reliable fireground communications and supports fireground simplex channels.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Technology
Repeaters — Improve Field Unit to Dispatch and Offscene Units
Receiver voters are one solution to get communications from a radio user to the dispatch
center, but another solution is needed to get the communication to other radio users. One
type of system that can solve this problem is a repeated radio system. Repeated radio
communication, also known as half duplex communication, uses two radio frequencies for
communication. The transmitting radio transmits on frequency 1 (F1), and that signal is received by the repeater. The repeater then repeats the transmission on frequency 2 (F2),
and this signal is received by the receiving radio. By locating the repeater on a high building or mountain, the range of transmissions from the transmitting radio can be more than
doubled, and can reach over obstacles effectively.
Another solution to improving communication between field units inside buildings or tunnels
and dispatch and offscene units is the bidirectional amplifier (BDA). BDAs can be used with
half duplex radio systems to extend coverage from inside the structure to the outside of the
structure and vice-versa, but BDAs do not operate with simplex radio systems.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Usage
VHF: Bendix / King Mobile Radios
Chino Valley Fire Department uses 2 types of Bendix King Mobile Radios:
GMH & GMH-plus, and Commander. The GMH has15 groups of 16 channels
per group. The GMH-plus has 25 groups of 16 channels each. This radio shows
“GMH plus” on the front right panel and has extra groups 16-25 to provide expanded area programming.
The operation of the two types of radios is much the same.
To Turn radio on: GMH: rotate left knob on radio front clockwise.
GMH-plus: press left volume knob inward
To Change Channels: Use the right side knob on the front of the radio.
To Change Groups: Push the # key on mic keypad, enter the number of the
group desired. Push the (ENT) key.
To Select a Tone
Turn off scan, priority and “TA” making sure there are no lighted indicators
above each button in the radio display. For radios mounted overhead, you
may need to sit higher and look at the radio closely to see if they are “on”.
From the keypad on the mic, select a “CG” tone (CTCSS) 1 through 16. The
radio will remain on that tone until changed by selecting another tone. This
applies to repeaters and channel guarded tacticals.
If the radio display shows an asterisk * and a number, that particular channel
always requires the tone shown after the * to be selected.
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(Continued next page)
CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Usage
VHF: Bendix / King Mobile Radios
VHF BK mobile radio continued:
These radios have 5 buttons on the face and are programmed (from Left to Right) as follows:
(MON) Disable the channel guard feature. This allows you to hear users who may not be
sending a CTCSS tone. It is recommended to turn “on” the Monitor function when using tactical freqs with mutual aid units assisting.
(SCN) Channel Scan:
Press the SCN button to start or stop scanning channels in the scan list. SCN will flash in
the display window. Scan operation occurs only during receive operation. To add or delete
the current channel from the scan list, turn scan off, press and hold the SCN button for 1
second or more. “SCN” will display on the screen for all channels in the scan list. You can
scan only the channels in the selected group.
(PRI) Priority Channel:
Press PRI button to activate priority feature. The priority channel will be the channel selected by the channel knob.
(TA) Repeater Talk Around:
Press the TA button to turn the repeater TALK AROUND on or off. When TA is on, the radio
transmits on the receive frequency of the channel, bypassing or "talking around" the repeater. This function may be used on any channel that is programmed to a frequency pair
(repeater channel).
(HOM) Home Channel:
Press the HOM button to go directly to the pre-programmed home channel. To set a different Home Channel, select the desired channel using the Channel Select knob, press the
HOM button, and hold it for more than 1 second until the arrow above the HOM button appears on the display. The new channel then becomes the Home Channel. You can set a
home channel for each group. Please note that some radios that are mounted above the
windshield make it difficult to see whether the above functions are “on”. They
will each show a lighted arrow in the display window above each button. You may need to
move higher to eye level with the radio display to be sure.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Usage
VHF: Bendix / King Portable “HT” Radios
Chino Valley Fire has three types of B/K portable radios. They are GPH, GPH-XP, and Commander. The GPH has 15 groups of 16 channels each while the GPH-XP has 25 groups of
16 channels each. The Commander has 25 groups with 20 channels.
Squelch knob: Rotate the squelch knob to the right until noise is heard. Rotate back to
the left until the “rushing” noise stops. If you consistently receive interference, rotate all the
way left until it clicks. This places you in “CG” (Channel Guard) mode. Avoid using CG with
mutual aid units.
To Change Groups:
Push the # key on keypad, enter the number of the
group desired. Push the (ENT) key.
To Change Channels: Use the rotary knob on top of the radio.
To Use The Tone Function (Repeater or Channel Guarded tactical): Set all switches on
top of the radio towards you, select the appropriate channel. Press the number of the tone
you wish to use. The channel display will momentarily show the tone selected. Important: if
the display shows an asterisk and number, you must always select that tone when using
that channel. (i.e. “BDCV15 *7” means you need to select tone 7)
To Use The Talk-Around “TA” (Direct) Function: Set the left switch on top of the radio
to “TA” (away from you). *This setting may disable the tone. The radio will transmit and receive on the receive frequency. If the radio has a “HI/LO” label on top of the radio this switch
functions as LO = “TA” and HI = “RPT”. Corrected labels available at the warehouse.
To Set Channels To Be Scanned: Set the (SCAN) switch on top of the radio to the (OFF)
position towards you. Push the (ENT) button to enter the channel into the scan program.
Use the channel knob to move through the channels in the group. Use the (CLR) button to
remove the channel from the scan.
To Use The Scan Function: Set the scan program as described above. Set
the (SCAN) switch to “ON” (away from you). Scan will flash in the display
window. Only the selected channels in that group will be scanned. To turn off
the scan mode, set the (SCAN) switch towards you (OFF) position. It is
recommended to always turn on “PRI” and “SCN” together to avoid missing
traffic on your priority channel.
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CHINO VALLEY FIRE TRAINING DIVISION
Radio Communication Usage
VHF: Bendix / King Portable “HT” Radios (Continued)
HT keypad lock: If your HT says “LOCKED” in the display, press and hold the function
(FCN) button until it unlocks. Press and hold again to lock.
Group scan: HTs and mobiles can scan more than one group. Press (FCN), then (PRI),
then (ENT) to turn on. Press the same sequence to turn off. The radio will scan any channels that were set to “SCN” in all groups. The display will show “- - Ch - -“ while scanning.
When stopping on a channel, it will show the group number first followed by the channel
within that group that is being scanned. “23 Ch 10” indicates you are receiving group 23
channel 10. There is currently no way to change this display mode to alphanumeric mode.
Operating Through A Repeater System:
Those channels which transmit on a different frequency than they receive, operate through
a repeater (duplex). To open the repeater you must broadcast the correct subaudible tone.
The tones for repeaters in our immediate area are listed on pages 30-32. When operating in
an area that the correct tone is unknown, test each tone separately, briefly keying the mic
after each selection. When you have selected the correct tone you will hear a carrier
squelch indicating you have opened the repeater and it is now re-transmitting on your receive frequency. Scan must be off.
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