{TESS+} VHF Training Module 1: Overview of two-way VHF/UHF radio networks Read more about {TESS+}: www.wfp.org/telecommunications-security-standards Email: [email protected] Session objectives • Describe a two-way radio system • Describe the difference between simplex and repeater operations Two-way radio communications • Two-way radio communication is a form of communication where both parties are involved in the transmission of information. • Push-to-talk (PTT) is an important aspect of a two-way radio where a PTT button activates the transmitter. When the button is released the radio switches to receive mode only. Two-way radio communications • Two-way radios are preferred because they are: • Flexible in programming as required and as licensed (VHF: 136-174MHZ) • Open standards • Frequency of use, intended use, location, and number of users will determine the choice of radio. Two-way radio communications - advantages • Advantages of a well-planned two-way radio system: • Instant communication (PTT) • Network independence • Call broadcast • Interoperability (iCOM, Motorola, RoIP: Radio over IP) • Emergency feature built in the device • Flexibility Two-way radio communications - contextual use To establish communication, the signal must be recognised. This is enabled through: - Carrier squelch - Tone squelch: – TPL (Tone Private Line) – SelV (Selective Voice) Two-way radio communications - simplex vs duplex • Two-way radios can operate in two modes: simplex and duplex 1. Simplex mode: – Radio stations communicate with each other directly, on the same frequency – No repeater or other device in between – Depends on the line of sight and radio output power Handheld radio range (simplex): approx. 5 – 7 km Mobile radio range (simplex): approx. 10 – 12 km Two-way radio communications - simplex vs duplex 2. Duplex mode: – When simplex operations in not available – Radio station transmits on one frequency and receives on a different frequency. – Repeater in between to extend the radio coverage • Full duplex mode – radio can transmit and receive simultaneously. • Half duplex mode – radio has to be switched between transmit and receive. Two-way radio communications (repeater) Question One VHF repeater is programmed with frequency: • Tx: 155.150 MHz / Rx: 160.150 MHz Q: What Tx frequency should be programmed in the user equipment e.g. handheld and mobile radios? Answer Receive (Rx): Transmit (Tx): 160.150 MHz 155.150 MHz Repeater Transmit (Tx): Receive (Rx): 160.150 MHz 155.150 MHz User equipment User equipment Basic components of VHF/UHF base radio station Antenna cable Power cable High gain antenna Lightning arrestor Radio DC battery Solar panel Inverter / DC charger Basic components of VHF/UHF mobile radio station Antenna cable Power cable Antenna Radio DC battery Antenna with magnetic mount Basic components of a VHF/UHF repeater station Repeater Tx radio Power Repeater Duplexer supply Rx radio Duplexer • A duplexer is a passive device used in radio communication to connect a receiver and a transmitter with different frequencies to a single antenna. • A duplexer needs to be ”tuned” to the correct frequencies. Duplexer functionality • With a duplexer the transmitter (Tx) and receiver (Rx) radios can share a common antenna (i.e. only one antenna is needed). Duplexer Block the Rx frequency Block the Tx frequency VHF/UHF network standards The {TESS+} standard security VHF/UHF network is implemented with analogue user access and includes two basic user features: -Basic PTT (push-to-talk) feature, where users can easily reach all other users in the UN security communications network -Sel-V features (i.e. see the call ID, stun radios remotely, generic alert feature). Questions and remarks.