Types

Conventional Vs. Trunked

• Conventional radios operate on fixed RF channels. Channel is selected by a user
• In multi-channel systems channels are used to separate purposes.
  • Specific function
    • Channel 1 - road crews talk to road maintenance office
    • Channel 2 - road crews talk to state highway dept. crews.
  • Geographic location
    • Taxi company uses one channel to communicate in the Boston, MA and a separate channel to communicate in the Providence, RI area.
• Scanning - Some conventional radios scan more than one channel for a valid transmission.
  • Primary selected channel at full volume and other channels in a scan list at reduced volume.
  • Scanning can be defined and preset. Channels not changeable by radio user.
  • Some radios allow an option for user-selected scan.
• Examples of some conventional radio types:
  • Marine VHF radio
  • Family Radio Service
  • UNICOM

• The system logic automatically picks the physical radio frequency channel. A protocol defines the relationship between the radios and the radio backbone which supports them.
• Digital trunked systems carry multiple conversations on one physical channel, also called multiplexing.
• Instead of channels, radios are related by groups which may be called:
  • Groups, talk groups, fleet, subfleet or agency-subfleet.
• Systems make arrangements for handshaking and connections between radios by one of these two methods:
  • A computer assigns channels over a dedicated control channel. The control channel sends a continual data stream. All radios in the system monitor the data stream until commanded by the computer to join a conversation on an assigned channel.
  • Electronics embedded in each radio communicate using a protocol of tones or data in order to establish a conversation.
• If all physical channels are busy, some systems include a protocol to queue or stack pending requests until channel is available.
• Visual cues of trunked system:
  • Lack of a squelch knob or adjustment
  • No monitor button or switch
  • A chirp (made infamous by Nextel), shows channel is available and ready the moment push to talk is pressed.
• Examples of trunked radio types:
  • Logic Trunked Radio
  • EDACS

Simplex Vs. Duplex

• Typical of aircraft VHF AM and marine radios.
• Often “legacy” systems, which have existed for years or decades.
• Architecture is simple enough for old radios to communicate with new ones in a single network.
• Advantage: Simplest system configuration, reliability from the fact that only two radios are needed to establish communication between them.
• Disadvantages: The simplex configuration offers communication over the shortest range or distance.

• Disadvantage: Systems where equipment cannot communicate without some infrastructure such as a repeater base station.
• Advantage: Repeater configurations are common in the US – base station is configured to re-transmit the audio received from mobile units… larger area than simplex system.
• Two types:
  • Half-duplex – push to talk switch is required to communicate.
  • Full duplex – systems like mobile phones capability to simultaneously transmit and receive conversations.

Analog Vs. Digital

• Advantage: In high-quality equipment, better ability to communicate in cases where a received signal is weak or noisy.
• Disadvantage: Only one conversation at a time can occur on each channel.

• Advantage: More simultaneous talking paths possible and information such as unit ID, status buttons, or text messages can be embedded into a single digital radio channel.
• Disadvantage: Radios must be designed to the same compatible standard, radios can become obsolete quickly, cost more to purchase, and may seem more complicated.

Engineered Vs. not engineered

• Engineered systems are designed to perform close to specification or standard.
• Integral systems with all equipment matched to performed together.
• Example: Cellular telephone system.
• Designers use a series of models to help choose equipment, locations, antennas, and estimate how signals will penetrate buildings.

• Legacy systems are not engineered. Never designed to meet a system performance objective.
• May have started as a base station and a group of mobile radios. Over years, the equipment added on in a building block style.
• May perform well even though not professionally designed as a coherent system.

Life of Equipment

Usage, atmosphere and environment plays a major role to decide its life term. Average life of two way radio is 5 – 7 years and 1 – 2 years for its accessories.