Two way radios, as discussed here, are limited to a direct unit-to-unit radio communication, either via single unit-to-unit transmission and reception, or via multiple hand held units to a base station radio contact and distribution system. Radio frequency spectrum limitations apply to all hand held units, as directed by the FCC. This also distinguishes a hand held unit from a base station to base station unit (such as those used by an amateur (ham) radio operator), which operate under different wave length parameters. (Point to point microwave transmissions are also outside of the scope of this evaluation.)

Two-way radios allow a user to contact another user or group of users instantly on the same frequency, and to transmit voice or data without the need for wires. They use “half-duplex” communications; or communication that can be only transmitted or received; it can not transmit and receive simultaneously. In other words, only one person may talk, while other personnel with radio(s) can only listen. To talk, the user depresses the talk button and speaks into the radio. The radio then transmits the voice wirelessly to the receiving radios. When the speaker has finished speaking and the channel has cleared, users on any of the receiving radios can transmit; either to answer the first transmission, or to begin a new conversation. In addition to carrying voice data, many types of wireless radios also allow the transmission of digital data, and these radios may be interfaced with computer networks that can use or track these data. For example, some two-way radios can send information such as global positioning system (GPS) data, or the ID of the radio. Some two-way radios can also send data through a SCADA system. SCADA communications are discussed in detail in the SCADA Product Guide.

Wireless radios broadcast these voice or data communications over the airwaves from the transmitter to the receiver. While this can be an advantage in that the signal emanates in all directions and does not need a direct physical connection to be received at the receiver, it can also make the communications vulnerable to being blocked, intercepted, or otherwise altered. However, security features are available to ensure that the communications are not tampered with. More details on these security features are provided below.

 

There are a number of parameters that affect radio performance, including the type of service the system provides, as well as the system’s power and the frequency on which the system transmits. However, most of these parameters are pre-set by the manufacturer, and thus users must determine their specific needs prior to purchasing a system, and then choose the system that best fits their needs. Once a specific radio system is purchased, user options will typically be limited to channel selection and power output, and even these options will only be available if the models are specifically configured so that the user can change these parameters.

Portable and mobile radios from Relm/BK Radio

Radios that operate on a long-range service (long-range radios) are programmed to transmit on a frequency that a repeater “hears” and then re-transmits at a higher power. The repeaters are typically mounted to unmanned towers or buildings to encompass large areas, such as a city or a county. Because of this greater coverage area, long-range radios are generally more appropriate during emergency situations; when personnel may have to communicate over a longer distance or between remote locations.

Long-range radios can be programmed to function like short-range radios through the use of “talk-around” channels. The talk-around channel uses a frequency that the repeater (which also requires programming) does not hear. This scenario would work well for “on-the-scene” responders who wish to communicate with each other and not clutter the main channel with their chatter. Both long-range and short-range radios can be configured to broadcast either secured or unsecured transmissions.

System Configuration

A radio system consists of at least two radios on the same frequency (or “channel”); however, any number of radios may be used on the same channel. When there are few individuals using the same channel, communication may be simple and straightforward, and users can communicate with each other directly. However, when there are many users using the same channel, communications may become more confused, especially if multiple conversations between different users are being held at the same time. To avoid problems like these, users can set up a base station or dispatch center to control communications. Personnel at the base station can support field units by relaying information and recording data sent from field units. More complex and sophisticated radio systems can be connected to a computerized base station [e.g., Computer Aided Dispatch (CAD)], which could include features such as GPS automatic location reporting, over-the-air programming for channel and encryption, and integrated mainstream software programs to manage the incoming information. These radio systems are often “trunked” (i.e., controlled and managed by a computer).

Model 807 Single Site Controller, Zetron, Inc.

 

Frequency

Very low frequency, or VLF, [30–54 mhz] has a range of approximately 150–500 miles, and can be used for long distance, statewide communications. While VLF systems enable users to communicate over long distances, this long transmission capability also increases the risk of interference from transmissions made by other, non-related users in nearby locations who may happen to be using the same frequency. VLF radio band waves are not easily translated into digital signals, which limits the ability of these types of systems to be effectively trunked or encrypted (see below for a discussion of encryption).

Very high frequency, or VHF, [134–174 mhz] is used today in pagers, taxis, and commercial businesses. VHF has a range between 25–150 miles. Emergency services still use this frequency for backup channels and medium-range mountain communications. VHF is suitable for trunking and encryption because its narrow-band waves are good for digitizing.

Ultra high frequency, or UHF, [401–512 mhz] has a range of between 5–15 miles. It is used in emergency services, for government agencies, and in limited commercial applications. This frequency range is best suited for inner city communications because it works well in concrete and steel buildings, and it is a popular choice for police and fire agencies. UHF signals are suitable for trunking and encryption because its narrow-band waves are good for digitizing.

Very ultra high frequency, or VUHF, [512–760 mhz] has a short range of 5–10 miles, and is used by military and commercial customers. Pagers and some older cell/satellite phones also use these channels. VUHF is very well suited for urban and inner city applications because it penetrates concrete and steel well. VUHF can also be trunked and encrypted because its narrow-band waves are good for digitizing.

Very high band/ultra high band, or VHB/UHB, [800–960 mhz] has a short range of 5–7 miles. Because its range is so short, it is rare that there will be interference from nearby users on the same frequency. VHB/UHB is currently used in cell phones, personal digital assistants (PDAs), pagers, and some newer satellite phones. VHB/UHB is very well suited for urban and inner city applications because it penetrates concrete and steel well. VHB/UHB can also be trunked and encrypted because its narrow-band waves are good for digitizing.

System Power

One of the main factors affecting the range of a two-way radio is its power output, or “wattage.” The amount of power a radio or radio system requires depends on its broadcast frequency, with higher frequency broadcasts requiring more wattage. However, high-frequency radio waves can also be harmful to human health (the human body can absorb high frequency waves, which can damage soft tissues, such as the eyes), and, therefore, radios with higher wattages that broadcast at higher frequencies (above 500 mhz) must be shielded to protect human health. For this reason, all portable radios are limited to 5 watts or less. Other types of radios, such as base stations and mobile units, can be more high-powered because the user is shielded from the antenna and the unit’s wave transmissions.

BK Radio GBH/GBV Desktop Base Station from Relm/BK Radio

 

 

 

 

 

Type	Power (Watts)	Antenna	Description
Base station	25–100	External antenna, which is usually mounted on the roof or an accessory tower, to maximize the system’s range.	Base station radios are installed at a permanent location (typically a communications center or some other location that is continuously staffed), and usually function as the communications center (see discussion of base stations under “System Configuration” above). Base stations can be as simple as a desktop unit that is connected to an outside antenna, or as complex as an enhanced computer-controlled system connected to a network and linked tower system.
Mobile	40 (maximum)	Exterior antenna, typically mounted on the outside of a vehicle in which the system is installed.	Usually permanently installed in a vehicle.
Portable radios [walkie-talkies]	5 or less	Unit has its own antenna	Usually carried by or on the person. Battery powered. Can be as small as a cell phone, or as large as a cordless home phone.

 

 

Options for Securing Communications

As mentioned above, threats to radio communications include the possibilities that the communications can be blocked. Because radio communications travel over the open airwaves, they are only slightly vulnerable to being blocked, resulting in the loss of a signal or communication. However, most occurrences of blocking would occur very close to the transmitter or receiver. Since two-way radios are often mobile, users can often move the unit to obtain better reception

Two-way radio communications are also vulnerable to being intercepted or altered. One method for ensuring that communications are not intercepted, or perhaps altered, is by encrypting them. Encrypting radio transmissions is discussed below.

Encryption

Encryption, which is the process by which communications are electronically encoded at the transmission end of a communication and decoded at the receiving end, is usually used to ensure privacy of voice or digital data. Encryption is available for most commercial-grade radios, although it requires some set-up after the radios are initially purchased. During the set-up, all of the radios that are to be used together are configured so that they can receive and transmit using the same encryption key stream protocols (see below), thereby making it more difficult for a non-authorized user to intercept and understand the communications. There are three basic levels of encryption security used today.

Low-level Encryption: Inversion

This method of encryption is based on “inverting” the signal during the transmission of a voice message. As it is transmitted, the signal is split into two bands: left (not inverted) and right (inverted). The left (not inverted) band is muted by the filter, while the right (inverted) band is amplified and transmitted in the 300– 3000 Hz range. The receiving radio, which must be set to operate at the same frequency inversion, picks up the scrambled signal and inverts it back to the original transmission.

Medium-level Encryption: Analog to Digital Conversion

460 Series, Icom America

The analog-to-digital encryption method converts the analog signal into a digital signal of ones and zeros, reverses it, and then splits this digitized signal into 22 new channels. The scrambled signal is then assigned a unique random key generated electronically from a base of over 2,048 keys. This encrypted data is then transmitted along with its unique key. As long as the receiving radio receives the correct key, it can translate the transmission back to the original voice.

 

 

 

 

High-level Encryption: Computer Digital Conversion

In computer digital conversion, the voice signal is digitized and then encrypted with a random key stream of 256 numbers that is generated at the beginning of each transmission. The encrypted voice is then converted into zeros and ones, and then the order of the zeros and ones is scrambled again. This encrypted data is then transmitted along with its unique key. As long as the receiving radio receives the correct key, it can translate the transmission back to the original voice. Anyone eavesdropping on conversations encrypted by computer digital conversion will hear only continuous static or white noise. Because there are over 4 billion keys available for encrypting, and each key is randomly selected with each transmission, this is the most secure type of encryption.

Encryption is a standard feature of some radio systems, and it may be able to be added to radio systems that do not include it by installing an encryption chip – as long as that specific radio model has the capability to implement an encryption chip. While five types of encryption chips are available, only three (DVP, DES and DVP/DES-XL) are typically used in commercial radios. The five types of chips are described below:

DVP (Digital Voice Privacy) is a Motorola protocol that uses a propriety encryption method. Options for this standard can be low, medium, or high encryption.

DES (Data Encryption Standard) is similar to DVP, but is used for data encryption instead of voice encryption. As with DVP, low, medium, and high encryption levels are available. See the Hardwired Voice and Data Communications Product Guide for additional information on encryption.

DVP-XL/DES-XL is a modification that is used for high level encryption modules. This type of encryption increases the number of keys available for key streaming relative to standard DVP. It can also minimize the possibility of losing range, which can occur in older radios.

DES/Output Feedback (OFB) is used by law enforcement and is compliant with their P-25 security protocols. This requires that all radios will interoperate with other agencies and equipment. It may be possible to purchase and use equipment with this type of encryption, but any user desiring to do so will have to evaluate FCC, local, state and federal regulations to determine if this is legal.

DVI-XL (Digital Voice International) is used by commercial contractors overseas and has fewer keys. It is not typically used in the U.S.

 

Radio Units

As described above, there are many different types of two-way radios, which range from simple, unsecured family radio service (e.g., the walkie-talkies that are sold as children’s toys) to military-grade radios. These lower-grade products can be very inexpensive (e.g., family radio service radios can cost as little as $20 at the local discount department store). However, these types of radios are unsecured, and service is not always dependable. Therefore, these types of radios may not be suitable for use at water or wastewater utilities.

Commercially rated two-way radios will be in the several hundred-dollar range. For example, a commercially rated two-way portable radio with entry-level encryption typically costs between $350 and $700. Mobile radio units with similar features cost approximately the same as portable units.

A quality simplex 4 channel base stations with entry-level encryption can cost between $1,100 and $3,000. A mainstream desktop 50-watt repeater radio costs approximately $3,500 to $5,000. Computer Aided Dispatch [CAD] base stations are custom solutions and range in price from $10,000 to more than $50,000 in some applications.

Antennas

Antennas and installation will vary by site and requirements; however, a quality base station VHF/UHF antenna costs approximately $800 to $1,000. A mobile antenna usually costs between $40 and $90 depending on its type and intended use.

Installation

Installation is required for each radio and antenna, and will be an extra charge. Expert installation is usually required because of Radio Frequency safety issues as discussed above. Portables will also require programming, and this can cost between $25 and $40 per unit.