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Narrow Band Digital Two-Way Radio by Kevin Poulter* Like just about everything else in the 21st Century, professional two-way radio is making the transition from analog to digital. As well as potentially much clearer signals and more users in the same amount of spectrum, digital two-way radio offers many other advantages. * on behalf of ICOM Australia siliconchip.com.au October 2013  53 Fig.2: Next Generation Digital Narrowband (the red line) has a much sharper range cut-off than analog audio (the blue line) but offers significantly better audio quality over its operating range. Fig.1: the older 12.5kHz-wide analog signal (on the left) occupies the same amount of bandwidth as two 6.25kHz digital signals (right). These can co-exist without interfering with each other. T owards the end of last century, the growing demand for radio frequency spectrum in the “Land Mobile” UHF professional two-way radio band forced a change from the original 100kHz separation between users down to 25kHz separation. But even this wasn’t enough to accommodate the ever-increasing demand. In the USA, the FCC mandated that all professional telecommunications equipment have a separation of just 12.5kHz by January 1, 2013, and Australia’s Communications and Media Authority (ACMA) followed suit. However, it’s widely expected that before too long, even this will be too wide and a separation between channels of just 6.25kHz will be required. Modern radio equipment, such as that made by Icom, already has this capability built in. Going digital Narrowbanding, as it is called, was the ideal opportunity for transceivers to also migrate from analog transmissions to digital. Not only does this enable many more users in the available spectrum, but it also enables improved noise rejection and voice quality over a greater distance. Much clearer (and therefore intelligible) conversations are especially evident at the limits of the transmission range, with none of the analog background noise. But digital transmission has a number of other benefits, such as the ability to further clarify speech by looking for waveform patterns which match an internal library of speech waverforms. Any other patterns – such as noise and even wind noise in the microphone - are assumed to be noise and are nulled out. Co-existing with analog With so many millions of dollars invested in analog radio equipment, many organisations would be most reluctant to replace their current system, digital advantages notwithstanding. For this reason, Icom developed a “mixed mode” system whereby analog and digital can co-exist and be used in parallel until the user is ready to replace old gear. For example, a leading Australian hospital currently has made the switch to digital inside the building but their security contractor still uses analog mobiles on the same channel. Both are received simultaneously with the system automatically adjusting and replying in the transmission mode in use. The same hardware – antennas, power supplies, duplexers, isolators and combiners can be used with both systems, so the only cost is adding digital transceivers as and when required. Next Generation Digital Narrowband A joint technical alliance between Icom and JVC Kenwood developed Next Generation Digital Narrowband IDAS single-site trunking (left) is for relatively small area use, with individual sites only able to communicate with units on their site. By contrast, multi-site trunking (above) can handle up to 48 sites, each with 30 channels. Communication is via an IP network and sites can be virtually anywhere, even on the other side of the world. 54  Silicon Chip siliconchip.com.au (NXDN) technology, an open protocol. Two 6.25kHz digital narrowband signals can be used next to each other within a 12.5kHz channel without causing interference to each other or adjacent channels. Internet connection Icom’s Digital Advanced System (IDAS) has a network interface which can be connected to a LAN or the internet. Communication range is vastly extended by talking through IP (internet protocol), eliminating the need for costly RF links or leased lines for “off site” communication. Hence, “off site” can be anywhere from the next street to the other side of the world. Trunking systems Insufficient spectrum, increased radio usage and budget limitation often mean there are insufficient channels available for users in large groups to have their own frequency. “Trunking” is a commonplace solution to this problem, where many users share relatively few radio channels and calls are automatically “routed” via a central computer. They are divided into “talkgroups” and the computer finds a vacant channel to allow the communication to proceed. Icom’s digital transceivers are capable of a variety of modes of trunking, with their “MultiTrunk system allowing from one to thirty channels per site, with up to 16 sites. All channels can be used for voice or data and a priority system allows emergency communication interruption. Coding, decoding and scrambling Digital communication allows advanced coding, with CTCSS (Continuous Tone-Coded Squelch System), DTCS (Digital Tone Code Squelch) and RAN (Random Access Number) coding on a per-channel basis. This allows the channel to be shared with multiple users, only springing to life when the code appropriate to the called station is received. Similarly, scrambling (for secure communication) is particularly suited to digital mode, without the significant loss of voice quality that analog scrambling can cause. In IDAS digital mode, a 15-bit encryption key can also be programmed, for over 32,000 scrambling codes. Easy programming Another feature of the digital age is quick and easy programming on site, from a suitably equipped PC. Features such as selective calling, status message, radio stun/kill/ revive (useful when equipment is stolen) and even GPS position reporting can be programmed into the system. Professional Telecommunications Narrow Band Digital has a host of features, far more than can be summarised here. If you’d like to know more, and see how the ICOM range fits into digital radio, visit SC www.icom.net.au Icom’s Digital Handheld transceiver has 512 memory channels with 128 zones, IDAS and NXDN features, GPS receiver, man down function, waterproof to IP67 standard and 800mW audio output power. siliconchip.com.au October 2013  55