1. Public Safety Radio Bands
VHF-Low Band: 25 MHz to 50 MHz
VHF-High: 138 MHz to 174 MHz
UHF: 408 MHz to 512 MHz
700 MHz (new)
800 MHz
4.9 GHz (new)
These are the most common frequency ranges used by public safety agencies in the United States.

2. Why is this a problem? Radios only operate in one band!
Multi-band radios are rare and expensive
If Agency A uses VHF and Agency B uses UHF, they can’t talk to each other UNLESS…
…They have planned ahead!
Two radios in a rig, etc.
The only multi-band radios currently on the market are actually two radios tied to a single control head. Dual band portable radios are not readily available…only mobile radios.
In this situation, pre-planning is extremely important. How will they communicate with each other? Will one department install two radios in their apparatus? If so, what is the protocol for contacting the other agency, etc.?

3. Propagation Basics- Free Space Path Loss
Path Loss (in dB) = 20 x Log[4d/]
Where: d is distance in meters
 is wavelength in meters
 = speed of light/frequency
So: as frequency increases, path loss increases
This means that if everything else were equal, a system at a lower frequency would reach farther than a system at a higher frequency
But…other factors are at play as well
This slide is only intended to show the general path loss trend. Don’t get lost in the math…not that important. The formula is for theoretical free space, not the real world, but it illustrates a trend.
Other considerations: Smaller antennas at higher frequencies means more efficient antennas are possible
“skip” more likely at lower frequencies
building & forest penetration characteristics of different bands
amount of spectrum (channels) available in a given band

4. Propagation & Band Characteristics
VHF Low Band (30-50 MHz)
Best propagation in undeveloped and hilly terrain–Poor building penetration
VHF High Band ( MHz)
Very good propagation in undeveloped and hilly terrain–Moderate building penetration
UHF ( MHz)
Good propagation in undeveloped and hilly terrain–Good building penetration
700/800 MHz
Poor propagation in undeveloped and hilly terrain–Very good building penetration–
700 currently subject to incumbent television stations in some areas
800 currently subject to interference from commercial carriers
4.9 GHz
Microwave propagation used for short range (Wi-Fi type) or point-to-point links
Better building penetration at higher frequencies is actually due to ability to more easily pass through openings, not penetrate through solid walls.

5. Frequencies vs. Channels
A frequency is a point in the radio spectrum
part of what describes a channel
A channel is a set of parameters that can include one or more frequencies, CTCSS tones, name, etc.
Example: VCALL is a channel with transmit and receive frequency MHz, CTCSS tone of Hz

6. CTCSS (PL) Tones PL stands for Private Line, a Motorola trademark
Other names include Code Guard, Tone Squelch, Call Guard, Channel Guard, Quiet Channel, Privacy Code, Sub-audible Tone, etc.
“Generic” term is CTCSS – Continuous Tone Coded Squelch System

7. What Are These Tones?
A PL tone is a sub-audible (barely audible) tone that is sent along with the transmitted audio
A receiver that has CTCSS decode (a.k.a. a receive PL tone) activated will only open its speaker if the correct tone is received
PL tones are different than tones used to set off pagers (two-tone sequential paging)
Remember…PL tones are sub-audible and continuous…they are being sent the entire time a radio is transmitting
Two tone paging uses audible frequencies (300 Hz to 2 kHz)
CTCSS uses frequencies below 300 Hz…the radio’s audio filter removes these frequencies, making the tone barely audible

8. Standard CTCSS Tone Table
These are the 38 industry standard tones. There are additional non-standard tones that are also being used.

9. What Are They Used For PL Tones are used to MASK interference
They DO NOT REMOVE INTERFERENCE
Useful for masking interference from computers, electronics, etc.
Useful for masking interference from “skip”
Should NOT be used to block out traffic from neighboring (nearby) departments
This is OK for taxis, etc., but not for public safety
Creates “Hidden Interference” problem – missed calls possible
If two neighboring departments use different tones, department A will not hear department B when they are talking. This might sound like a good thing, but it is not!
Example:
Portable radio from department A wants to talk to the fire station of department A. The user keys up and calls for the fire station, but unbeknownst to him, the dispatch center for Department B is talking on the same frequency at the same time. The portable radio user doesn’t realize this because his radio doesn’t open the speaker unless the correct tone is received. Fire station A never hears the portable radio talking because the neighboring dispatch center’s signal is much stronger than the portable signal and overpowers it. The radio at fire station A never makes a sound because the overpowering dispatch center signal is transmitting the wrong tone. The result? The call goes unheard.

10. What Are They Used For (cont.)
Used to activate remote links
Used to access repeaters

11. DCS – Digital Coded Squelch
A.k.a. Digital Private Line (DPL)
Similar to CTCSS, but uses a digital code instead of an audio tone
Used on analog radio systems, even though it is a digital code

12. Encode vs. Decode PL (or DPL, et.c) Encode means to transmit the tone
Decode means that the receiver will listen for the tone and not let anything through unless the correct tone is received
TX and RX tone can be different
Radio can be set to TX tone but have no RX tone (all traffic is received)
If in doubt, don’t program RX tone
“Monitor” function bypasses RX tone
Unless you are sure that all radios you’ll want to talk to will be transmitting a tone (or DCS code), don’t program in an RX tone. If you do, you won’t be able to hear radios that are on the same frequency but aren’t transmitting the tone (or code) unless you manually use the “monitor” function.
On mobile radios, the monitor function is usually tied to the mic hangup clip (when the mic is removed from the clip the radio goes into “monitor” mode). On portable radios, the monitor function is usually a button on the side of the radio next to the PTT button.

13. Simplex Very Reliable Limited Range Radio Channel uses 1 frequency
2-5 mile range for portable to portable communications. Up to 20 miles possible mobile to mobile or mobile to base.

14. Duplex
Radio Channel using 2 frequencies, Freq 1 to talk from radio A to radio B, and Freq 2 to talk from radio B to radio A
Each user must be line of sight with each other
Examples: Cordless Telephone systems, which both parties can talk at the same time and listen at the same time. f1
Duplex is possible without a repeater, but this is not often used in public safety (few exceptions). f2

15. Base Station – Height Improves Range
Some units don’t hear transmission because of obstructions
In this case, when Unit 2 talks, Unit 1 and the dispatcher can hear the transmission. However, Units 3 and 4 are out of range of Unit 2 because of the obstruction (mountain). In order for Unit 2 to communicate information to Unit 4, the dispatcher must relay the message.
Unit 1
Dispatch Center
Unit 4
Unit 2
Unit 3

16. Base Station – Height Improves Range
Dispatcher relays message – heard by all units
When the dispatcher talks, all units hear the message because the base station antenna is elevated.
Unit 1
Dispatch Center
Unit 4
Unit 2
Unit 3

17. Remote Base Operation Remote Link Unit 1 Unit 4 Unit 2 Unit 3
Dispatch Center
Remote Link
Microwave, Phone Line, etc.
Remote link connects dispatch center to base station. Link can be via a phone line, microwave link, UHF link, etc.
This setup is commonly used in Tazewell county. The base radio at the fire station (or somewhere in the community) is tied to the dispatch center via a remote link.
Unit 1
Unit 4
Unit 2
Unit 3

18. Conventional Repeater
Receives a signal on one frequency and retransmits (repeats) it on another frequency
Placed at a high location
Increases range of portable and mobile radio communications
Allows communication around obstructions (hills, valleys, etc.)
User radios receive on the repeaters transmit frequency and transmit on the repeater’s receive frequency (semi-duplex)

19. Conventional Repeater
Dispatch Center
All units within range of repeater hear all transmissions through the repeater f2 f2 f2 f2 f1
When a user keys the radio microphone, the radio automatically switches frequency from the its receive frequency to its transmit frequency. The repeater’s receive frequency is the same as the user’s transmit frequency, so it hears the transmitted signal. It instantaneously retransmits that signal out on the frequency that the rest of the users are listening to (their radio’s receive frequency).
Unit 1 f2 f1 RX TX
Unit 4
Unit 2
Repeater
Unit 3

20. Conventional Systems Communicating PD 1 PD 4 Idle PD 2 PD 3 Idle FD 3
When one user is talking, other users on that channel are cannot talk, even though other repeaters in the area may be idle.
Communicating
PD 1
PD 4
Idle
PD 3 cannot talk to PD 4 because PD 1 is using the repeater
PD 2
PD 3
If many groups need their own repeaters, it can tie up a lot of resources (towers, frequencies, etc.), especially if some groups only use their repeater intermittently.
Idle
FD 3
FD 1
Public works repeater may be idle 90% of the time, which means that frequency is largely wasted
PW 1
FD 2
PW 3
PW 2

21. Trunking
Trunking is a method of combining repeaters at the same site to “share” frequencies among users
Spectrally efficient
Allows many more “virtual” channels (called talkgroups) than there actually are frequencies
Computer controlled
Trunking systems can be more efficient and cost-effective than conventional systems when more than about 5 channels are needed. Instead of having to install 15 repeaters, only 5 trunked repeaters may be needed (depending on traffic volume).

22. Trunked System f1 f3 f4 f2 f2 f2 f1 RX TX f4 f3 RX TX f6 f5 RX TX PD 1
FD 1 f4
FD 2 f2
PD 2 f2
PD 3
Frequencies are dynamically assigned by system controller
User radio may be on a different frequency every time it transmits
Talkgroups are “virtual” channels
Possible to have many more talkgroups than actual frequencies
Statistically, not all talkgroups will be active at the same time f2 f1 RX TX
Multiple user groups utilize the same tower sites and frequencies. The system controller assigns frequencies as they are available on a priority basis. f4 f3 RX TX
System Controller f6 f5 RX TX
Shared Repeater Bank

23. Trunked System Operation
User radios continuously monitor a dedicated “control channel”
When a user wants to transmit, the user’s radio makes a request to the system controller
If a repeater is available, the system controller temporarily assigns that repeater channel to the talkgroup making the request
Transmitting user’s radio will give a “talk beep”, indicating that a repeater has successfully been assigned…user can talk
All user radios monitoring that talkgroup automatically switch to the frequency of the assigned repeater and hear the transmission
When the transmission is complete, all radios return to monitoring the control channel

24. Multi-Site Systems Conventional Trunking
Repeaters on same output, different input
Linked repeaters on different frequencies
Remote Receive Sites
Voting
Simulcasting
Trunking
Roaming

25. Repeaters on same output frequency, different input frequency (or PL tone)
Only one repeater active at a time
Users must manually change channel to different repeater depending on their physical location

26. Repeaters on same output frequency, different input frequency (or PL tone)
Only one repeater active at a time
Users must manually change channel to different repeater depending on their physical location

27. Linked repeaters on different frequencies
Both repeaters active at the same time with same traffic, but on different frequencies
Link (microwave, phone line, etc.)
Users must manually change channel to different repeater depending on their physical location

28. Voting Receivers Voter
Voter (comparator) chooses best received signal and sends that signal to the transmitter
Voter
Central Transmitter
Link (microwave, phone line, etc.)
RX Only Site
Users do not need to change channel depending on location. System (voter) automatically picks best receive tower site.

29. Simulcasting
Both repeaters transmit at the same frequency at the same time
Link (microwave, phone line, etc.)
Transmitters must be carefully synchronized to prevent interference in overlap areas

30. Analog vs. Digital Modulation
Analog versus digital modulation refers to how the human voice is transmitted over the air. In a digital system, the audio signal is first converted to ones and zeros (a digital signal) and then sent over the air. In an analog system, the signal being sent over the air is a continuous analog signal.

31. Common Analog Modulation Schemes
FM – Frequency Modulation
AM – Amplitude Modulation
SSB – Single Sideband AM
Almost all analog public safety communications use FM
AM is used for CB radio, aircraft communication

32. Frequency Modulation (FM)
To modulate means “to change” or “to vary”
Frequency Modulation means changing the frequency of the transmitter in proportion to the audio being picked up by the microphone
The receiver detects the change in transmitter frequency and uses it to reproduce the audio signal at the speaker
We’re used to thinking of radios as operating on a set frequency. That frequency is actually the center frequency around which the transmitted signal varies in proportion to the audio signal. How far the transmitted signal varies from the center is the “deviation” of the signal.

33. Frequency Modulation – An Illustration
Microphone Output:
Transmitter Output:
These two graphs are a very simplified illustration of how an audio signal changes (modulates) the radio transmitter. The graph on the left shows the voltage produced by a microphone that is picking up an audio signal. The graph on the right shows the corresponding transmitter output frequency of an FM transmitter being driven by the same audio signal. Note that an increase in microphone voltage causes a corresponding increase in transmitter frequency and vice versa.

34. FM Radio Block Diagrams (simplified)
Transmitter
Receiver
In an FM transmitter, the audio sound waves are converted to an electrical voltage via a microphone. The modulator produces the RF signal, which varies in frequency in proportion to the voltage produced by the microphone. This frequency-varying (frequency modulated) signal is then sent to a radio frequency amplifier and out to the antenna.
In an FM receiver, the signal is picked up by an antenna, detected (not shown), and sent to the demodulator, where the changes in the signal’s frequency are converted back into an analog voltage. This analog voltage is then amplified and sent to a speaker, which reproduces the audio sound waves that were picked up by the transmitter’s microphone.

35. Digital Modulation
Signal from microphone is converted from a voltage into numbers through a process called sampling
Those numbers are processed by a computer
Binary information (ones and zeros) is sent over the air instead of analog (continuous voltage) information

36. Sampling
To convert the analog signal to a digital format, the signal is sampled at regular intervals (approx once every 100th of a millisecond). By sampling, we simply mean measuring the signal voltage at that particular instant in time. The measured voltage is converted to a number in binary form (ones and zeros). In this example, the measured voltage might range from 0 to 2 volts, with 255 corresponding to 2 volts and 0 corresponding to 0 volts.
Once the analog waveform has been converted to a stream of numbers, those numbers can be processed through an onboard computer.

37. Frequency Shift Keying – An Illustration
Digital Bitstream:
Transmitter Output:
Frequency shift keying (FSK) is just one example of a modulation technique that can be used to send digital (binary) information.
Other common digital modulation schemes include phase shift keying (PSK) and quadrature amplitude modulation (QAM)

38. Vocoding
Vocoding is used to reduce the amount of data that needs to be sent over the air
Used to reduce necessary bandwidth – conserves spectrum
“Compresses” digital audio – analogous to .mp3 versus .wav audio files
Uses known human speech characteristics to “fill in gaps” of data that is removed
Transmitting the entire raw bit stream over the air would take too much bandwidth because overhead (additional information) is required.
The purpose of a vocoder is to remove information in order to reduce the required signal bandwidth. It removes information that it thinks is not needed using advanced algorithms.
Overhead includes Forward Error Correction (FEC), etc.

39. Digital Radio Block Diagrams (simplified)
Transmitter
Receiver
In the transmitter, the sound waves impact the microphone, which produces a voltage that varies with sound intensity. This voltage is sampled by the Analog to Digital Converter (ADC), and is turned into a string of data. This string of data is fed into the vocoder, which effectively “compresses” the data using a parametric algorithm. The data string exiting the vocoder contains less information than the data string entering it. This encoded data string is then sent to the modulator, which turns the data string into an RF signal, which is then amplified and sent out the antenna.
At the receiver, the RF signal is picked up by the antenna and sent to the demodulator, which turns the RF signal back into a digital data stream. This compressed digital data stream is then sent to a vocoder, which decodes the data into what should be (ideally) the original raw digital stream. This digital stream is then sent to a digital to analog converter (DAC), which converts the digital stream back into a voltage, which is used to drive a speaker and reproduce the sound waves.

40. The Digital Radio “Problem”
Parametric vocoder uses known human voice characteristics to encode and decode data
When background noise (non-human noise) is present, vocoder doesn’t always know how to respond
Unpredictable results (garble, loss of communication, etc.)
In a similar situation, an analog radio would transmit the background noise right along with the intended audio (background noise might overpower voice, but some audio is still received)
This problem was identified by the International Association of Fire Chiefs in early This is a problem common to all digital audio systems that use parametric vocoding (cellular, two-way, etc.)
Digital Voice Systems recently came out with an “improved” P25 codec for public safety use.

41. Possible Permutations
VHF Analog Conventional Simplex
UHF Analog Conventional Simplex
800 MHz Analog Conventional Simplex
VHF Analog Conventional Repeater
UHF Analog Conventional Repeater
800 MHz Analog Conventional Repeater
VHF Digital Conventional Simplex
UHF Digital Conventional Simplex
800 MHz Digital Conventional Simplex
VHF Digital Conventional Repeater
UHF Digital Conventional Repeater
VHF Analog Trunking Repeater (very rare)
UHF Analog Trunking Repeater (rare for public safety)
800 MHz Analog Trunking Repeater
VHF Digital Trunking Repeater
UHF Digital Trunking Repeater
800 MHz Digital Trunking repeater

42. Narrowbanding Deadline: 2013

43. What is Narrowbanding?
Effort by FCC to increase the number of useable radio channels below 512 MHz
Advances in technology allow signals to take up less bandwidth than in the past
Regulations are changing to take advantage of new technologies
Starting 2013, all radio systems must be narrowband compliant
Note that this only applies to VHF and UHF systems MHz is not affected by narrowbanding (it is affected by Rebanding)

44. What is Narrowbanding? (cont.)
Splits 25 kHz wide channel into two 12.5 kHz wide channels
When technology permits, there will be another migration to 6.25 kHz technology
For FM (analog) systems, narrowbanding is accomplished by reducing the transmitter’s FM deviation – receiver must compensate on the other end
Caveat: Moving to 12.5 kHz does not require going to digital, but in the future, moving to 6.25 kHz will require migration to digital, since analog FM will not work in a 6.25 kHz bandwidth. Migrating to digital means dealing with the aforementioned vocoder problem. As of this time, the FCC has decided not to set a date for migration to 6.25 kHz, but they want it to happen someday.

45. Existing VHF Systems: Already a problem
Existing VHF Systems: Already a problem. Not able to use adjacent channels at close distances.
20KHz Bandwidth
WideBand
WideBand
WideBand
Overlap
Overlap
Adjacent channels
15KHz Channel Spacing
15KHz Channel Spacing
Joe Kuran Oregon SIEC

46. After Narrowband: Still a problem Narrowband channels not usable until wideband users vacate.
20KHz Bandwidth
20KHz Bandwidth
Wide Band
Wide Band
20KHz Bandwidth
Overlap
Overlap
Wide Band
ANALOG
NARROWBAND
ANALOG
NARROWBAND
7.5KHz Channel Spacing
11KHz Bandwidth
Joe Kuran Oregon SIEC

47. After all convert to Narrowband Still some overlay with analog modulation
This represents analog voice with a 11KHz necessary bandwidth
ANALOG NARROWBAND
ANALOG NARROWBAND
ANALOG NARROWBAND
ANALOG NARROWBAND
ANALOG NARROWBAND
7.5KHz Channel Spacing
11KHz Bandwidth
Joe Kuran Oregon SIEC

48. Convert to Project 25 Digital Phase I Digital Modulation allows tighter packing of channels
Still a very minor overlay in the VHF band UHF band will have no overlay because of 12.5KHz Channel Spacing.
P25 with C4FM Modulation only requires 8.1KHz Necessary Bandwidth
DIGITAL
NARROWBAND
DIGITAL
NARROWBAND
DIGITAL
NARROWBAND
DIGITAL
NARROWBAND
DIGITAL
NARROWBAND
8.1KHz Bandwidth
7.5KHz Channel Spacing
Joe Kuran Oregon SIEC

49. What Do I Need to Do? Update FCC License
Obtain narrowband-capable radios
Program all radios for narrowband operation (at the same time)
DOES NOT require moving to 800 MHz or digital (although those are options)
FCC License should be updated to include narrowband emission designators
Use radio programming as an opportunity to add interop channels, standardize channel names, etc.

50. Why New Radios?
Narrowbanding halved a frequency’s bandwidth and deviation.
Many older wideband radios will not operate on frequencies set 12.5kHz apart (154.XXXX instead of 154.XXX)
An older wideband radio’s bandwidth is 25kHz. This would interfere with both new 12.5kHz narrowband frequencies on either side of the old 25kHz frequency.
An older wideband radio’s deviation is 5kHz. New narrowband radios will respond to this signal by either:
Not process the wideband deviation into a received audio signal.
Process it into a bad received audio signal (garbled, distorted, etc.).

51. Migration Problems
Problems can occur when both wideband and narrowband are used to communicate on the same channel.
Channels are programmed for either wide or narrowband.
Channels must be programmed consistently for all radios in use.
Narrowband Radio Transmitting to Wideband Radio:
Received audio may be very soft and quiet.
Caution, wideband radios must turn up volume to hear. However, once a second wideband radio transmits, the original wideband radio’s received audio will become very loud.
Wideband Radio Transmitting to Narrowband Radio:
Received audio may be loud, distorted, or inaudible.
Caution, if you turn down the volume, narrowband communications may not be heard.
Migration to Narrowband must be planned for all users of the channel!!

52. Failure Modes & Backup Plans
System Reliability
Failure Modes & Backup Plans

53. Rebanding
800 MHz Only

54. What is Rebanding?
Nextel (and smaller, similar systems) caused interference to some public safety 800 MHz radio systems
To solve this problem, Sprint-Nextel is paying to change the frequencies of every public safety 800 MHz radio system in the country that could potentially be affected
Depending on the system, this may only require reprogramming all radios, or it could mean replacing all radios
See for more info

55. System Failure, Reliability, Backup Plans

56. Possible Points of Failure
User Radio
Vocoder
Loss of Power (dead battery)
Repeater
Loss of Power (downed power line)
Antenna Failure (windstorm)
Catastrophic Site Loss (Tornado)
Link (T1 line, microwave link, etc.)
Loss of Power
Antenna Failure
Utility Outage (phone line)
For each possible failure mode, a backup plan must be in place, and users must be trained how to operate when the failure occurs.

57. Patrol Officer to Dispatch
Key – Choose the most reliable communication path possible for the job at hand
Patrol Officer to Dispatch
Most reliable path is a repeater because many times the officer will be out of range of the dispatch center
Firefighter to IC
Most reliable path is simplex because of the short range involved. Repeater failure is no longer an issue, nor is being out of range of the repeater.
Different situations may call for different communication systems or paths. What is best for one agency in one situation isn’t always best for all agencies in all situations. Use what is most reliable. Users must understand what is the best communications path and know how to choose it and use it.

58. Mitigation Techniques
Hardened Sites
Backup Power
Redundant/Backup Sites
Overlapping Coverage
Preplanning (i.e. radio programming)
Portable/Transportable Systems
User Training
You must know how every part of the system works in order to plan ahead for possible failures. If you don’t know how your radio system works or what its points of failure are, find out!

59. Interoperability & Mutual Aid

60. Nationwide Mutual Aid Channels
VCALL & VTAC (VHF Narrowband)
UCALL & UTAC (UHF Narrowband)
ICALL & ITAC (800 MHz)
These channels can be used by ANY agency for inter-agency communications (police to fire, state to federal, etc.)

61. Preplanning is Key to Interoperability
Radios must be programmed with mutual aid & interop channels beforehand
When the “big one” hits, it’s too late
Program as many mutual aid channels into radios as you have capacity for
Establish communications (make sure they work) before going into the field
Common naming convention is important
Even if you don’t plan to travel to large incidents out of your area, when an incident occurs in your area and outside assistance come in, they won’t have your local channels programmed into their radios. If everyone has the mutual aid & interop channels pre-programmed, communications are possible.
In past incidents, sometimes radios had the same frequencies programmed into them but were called different names, so people didn’t know that they could talk to each other. Common, nationwide naming convention has been proposed. Use it!

62. Practical Tips
Hold radio in hand for maximum range (radio on belt with speaker mic greatly reduces range unless remote antenna is used)
Don’t swallow the mic – 2 inches away
Don’t yell – causes overdeviation, distorts audio, unreadable
Know how the radio works – scan, priority scan, scan resume, talkaround, monitor, etc.
Ensure the channel is correctly programmed for narrowband or wideband operation (if this isn’t an option in the radio, it’s probably not narrowband capable)
Use consistent channel names when programming