You may have seen the photo of a police officer in a squad car sitting next to several mobile or portable radios. Each radio gives access to a different radio network or frequency band. If this picture could speak, it might say ‘why isn’t there a single radio that can replace all of these?’. Technology has answered this question with the development of multiband radios.

Many public safety radios today are single-band devices. They have been designed and tuned to operate in just one of the following specific frequency bands:

• 66-88MHz (known as VHF mid band)
• 136-175MHz (known as VHF high band, widely used for LMR around the world)
• 200MHz – VHF Band III, used in the United Kingdom
• 300-400MHz – UHF specialist use, eg military
• 380-470MHz (referred to as UHF 1,widely used for LMR around the world)
• 450-520 (referred to as UHF 2, widely used for LMR around the world)
• 700/800MHz (Commonly used in North America)
• 900MHz (Sometimes  used in North America)

It is not uncommon for a public safety agency to run networks in two (or three) of these bands e.g. UHF (which has better in-building coverage] plus VHF (which has better range) or VHF plus UHF plus 700/800 MHz. This means that officers who require access to each network may need to be equipped with two (or three) appropriate radios– one for each network. Alternatively, they can have a single multiband radio capable of operating in two or more frequency bands. All in the same unit.

Multiband radios available in the market today typically cover three bands, VHF, UHF, and 700/800MHz.

“All Band” Radios

Some radios in the market are misleadingly described as  ‘All-Band’ when, in reality, they operate in several selected bands. “All band” radios typically only cover VHF High band 136-174MHz,  UHF 380-520MHz, and 700/800MHz, and typically do not cover other bands such as VHF Mid band 66-88MHz, 200MHz or 900MHz.

Dual Band Radios

Many agencies find that two frequency bands are all they ever need and so refer to their multiband radios as ‘Dual Band’. Australian law enforcement, for instance, is restricted to VHF and UHF bands. A multiband radio can transmit and receive calls on any one of the available frequency bands.

Multiband Antennas

An important difference between a single-band radio and its multiband counterpart lies in the antenna you need to support the ability of the radio to transmit and receive. The reason is obvious once you think about it. Because a VHF/UHF multiband portable must handle both longer wavelength VHF signals as well shorter wavelength UHF operation, its antenna will need to be longer than the standard UHF antenna. The same considerations apply to other bands such as 700/800MHz. The size of an antenna should be directly proportional to the wavelength of the signal transmitted or received. Selecting the right antenna for your multiband radio is therefore critical for its performance. Getting it wrong may mean struggling with a radio that does not work as intended.

Multimode and Multi-protocol

Multiband should not be confused with multimode. Whereas a multiband radio supports more than one frequency band, a multimode radio can mean either:

• • (Type 1) A radio that supports several operating modes of the same radio technology or protocol
    • For example, P25 or DMR, not both
    • A P25 radio may support several of the following modes:
      • Analog conventional
      • P25 conventional
      • P25 Phase 1 trunking
      • P25 Phase 2 trunking)
    • A DMR radio may support several of the following modes:
      • Analog conventional
      • Analog trunking
      • DMR Tier 2 Conventional
      • DMR Tier 3 Trunking

• (Type 2) A radio that supports two or more different radio technologies or protocols (such as DMR and P25) in the same radio.

Type 1 multimode is becoming a standard offering in both single-band and multiband radios. In contrast, Type 2 multimode or multi-protocol radios are not yet widely available.

Crossband

Related to multiband operation is crossband operation. “Crossband” can mean that a call received on one frequency band (for example, VHF) is automatically repeated or transmitted on another band (such as UHF). Another meaning of “Crossband” is dual-transmit functionality whereby the radio can simultaneously transmit on two frequencies. Crossband operation is a specialist capability not commonly found in most multiband radios. Crossband applications require careful consideration and design. and are  supported by some radio vendors (such as Tait) with custom configurations, and by providers of vehicular repeater products such as Pyramid Communications.

Scanning

Whether single-band or multiband, a radio can be programmed to automatically scan each channel in turn looking for traffic. When activity is detected, the radio locks onto that channel and diverts its audio to the radio’s speaker. Both kinds of radio support a variety of scanning operations (e.g. priority scanning, background scanning, talkgroup scanning etc.).  And both allow the scan list of channels be Type 1 multimode e.g. any mixture of analog, P25 conventional, P25 Phase 1 trunking, or P25 Phase 2 trunking.

But where scanning on multiband radios differs is that the scanning can cross frequency bands. The scan list can include channels from any band the radio supports. For example, an agency that has a rural VHF system as well as an urban UHF system, can scan channels from both via the same radio. This capability gives multiband radios enormous operational flexibility.

Roaming

What about operating across systems belonging to different agencies which may need to share communications when an incident arises? (For instance, Fire, Law Enforcement, and EMS responding to a major traffic accident.)  In an emergency, radio users need the ability to collaborate by moving seamlessly from the operational area of one system to the operational area of another system – without changing the operating identities (individual and/or group) of the radios. Interoperation across different systems – called roaming – is made a great deal easier with multiband since there is no longer a need to share bands or frequencies to inter-operate. Of course, roaming doesn’t happen by magic. Let’s look at this in a little more detail.

There is a great deal of preliminary work that needs to be done once system owners agree to cooperate. Systems must be configured to identify and authenticate each other and their respective pools of radio units. And radios must be programmed to allow managed access – including scanning access – to neighbouring systems. Nevertheless, no extra infrastructure equipment is required to enable connection to multiple agencies and to allow roaming on their networks in any band. Multiband just makes this easier.

The key is to set up a network of systems that want to interconnect. Each such system is fully independent, administers itself, and has its own id.  For the purposes of inter-operation, however, they are all identified as belonging to the same wide area network. This is analogous to the law enforcement agencies of a county that are separate but are identified as belonging to the same county.

The simplest case is the agency that has a rural VHF system as well as an urban UHF system. The two systems are distinguished by their system id. Roaming across these systems is a must for officers of this agency. Now, by identifying both the rural and urban systems as belonging to the same wide area network, roaming is straightforward.  So, for roaming to work without additional infrastructure equipment, it doesn’t matter if the systems belong to the same agency or to different agencies, the essential feature is that they share the same wide area communications id.

Conclusion

We’ve looked at some of the obvious benefits of multiband: 

• reduction in the number of mobile and portable radios in your fleet if you no longer need multiple single band radios
• enhanced scanning 
• easier roaming.
• widening interoperability

I’d like to finish by mentioning a few multiband ideas that may be less obvious:

• A direct mode call is directly radio-to-radio, without passing through a network. Using the radios’s multiband capability in combination with roaming and multimode (Type 1) you can make off-network direct mode calls in an incident area using another agency’s frequency band

• If your single-band network has run out of spectrum and channel capacity, but no more spectrum is available in that band, you could add channels from a new band and use a multiband radio to communicate with radios on either your new or your existing channels.
• If you are migrating your entire system to a new band, with multiband you can access both your old channels and new channels during the rollout and gradually transition to the new network, thus smoothing out the migration process.
• Adding some backup channels in a different band can help to guarantee continuity of critical communications in the event of a network failure impacting your standard channels. A multiband radio can seamlessly switch to the backup channels and scan as required until the network is fully restored.