Business & GA, Commercial

Avionics System Design: P25 Radios: What’s in Stock?

By Walter Shawlee 2 | July 1, 2001
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AS WAS REPORTED LAST month, the technical scope of Project 25 (P25) radio systems is broad. It provides the long-term communication compatibility path desired by government and public safety agencies and their respective aircraft contractors.

To refresh your memory, it's important to remember that P25 radios are intrinsically capable of both digital and analog operation. P25 systems also support advanced features like multilevel encryption, group and station calling, wide- and narrow-band operation, positive unit identification, future over-the-air rekeying (OTAR), and optional automatic mode control to correctly respond to the incoming signals of any mode. These are significant operational enhancements, compared to the older FM radios, and this was a major driving force behind the change of equipment among government agencies in the United States. Also, P25 systems are compliant with older standards, to insure the widest possible operational compatibility.

Once you have decided to acquire a Project 25 radio, the next major hurdle is to find a unit that will integrate smoothly with your operational requirements, budget and cockpit space. Many agencies are acquiring this equipment now for all new purchases; others are establishing a procurement window of several years for fleet-wide adoption or contract compliance. The availability of P25 systems ranges from off-the-shelf to later this year.

The three main tactical FM radio suppliers for general aviation each have taken a different approach towards delivering P25 compliance, and their products reflect their design strategies and product suites. Each route has its own appeal. All P25 systems currently are in their phase-one stage, and offerings will increase and improve over time.

Northern Airborne Technology

Northern Airborne Technology Ltd. (NAT) has created an adapter, the NTA01, to repackage existing Motorola Astro P25 designated radios for aircraft use. The NTA01 translates tuning data from NAT's Dzus-mounted tac/com control head and provides proper DC power to the radio, as well as a robust mounting frame. The system requires a TH-series control head (with appropriate interface cards), an interconnect harness, and a remote transceiver. The package allows an existing tac/com installation to add P25 radio capability in any specific bandsplit supported by an Astro radio, with up to four radios operated from a single tac/com control head location.

Tradeoffs to this approach are the weight of the remote units and the interconnect, which can be significant; support for only a subset of Astro radio P25 functions (physical control head limitations); and radio frequency programming, which cannot be done in flight. The remote radio must be programmed using a laptop and Motorola RSS software, which transfers data to the tac/com control head. This programming operation can be done in the aircraft without equipment removal, however. In-flight user channeling (agile operation) is not possible from the control head.

Projected phase-two development at NAT will port P25 capability into NAT's NPX138 radio, providing a P25 compliant unit with agile operation. Deliveries of the NTA01 are scheduled for summer of 2001.

Wulfsberg Electronics

Wulfsberg Electronics, creator of the famous RT9600 airborne FM radio, has decided to add a P25 compliant radio subsystem from Motorola to its remote RT5000 broadband transceiver (in place of the system guard receiver). This is accomplished in two band sections, less than 400MHz and greater than 400MHz, but only one can be active at a time. This new dash number transceiver is then used with upgraded C5000 control head software to run two independent radio systems from a single cockpit control: one P25 compliant and one conventional (broadband). A system requires the control head, interconnect harness, and remote transceiver with new P25 hardware added.

Like the NAT approach, the user tradeoffs are similar: remote system weight and radio programming in place via a laptop computer, without unit removal. Both the control head and P25 subsystem on the Wulfsberg solution must be programmed; a user in-flight cannot perform agile channel changes.

RT5000/C5000 customers can upgrade their systems to this new level, and deliveries are expected later in 2001. The U.S. Customs Service and Los Angeles (Calif.) Police Department (LAPD) will be the Wulfsberg system's major launch customers. Phase-two development will port P25 capability directly into an agile radio system at some point in the future.

Technisonic Industries

Technisonic Industries elected to build a complete, fully tunable and programmable P25-compliant agile radio into their well-known Dzus format radio. The new radio requires no remote transceiver or support harness. Technisonic's system consists of the Dzus-mounted TDFM-136 transceiver alone, which is a significant weight and space saver in an installation. The company is developing radios in UHF and 800MHz bands now. These will be introduced soon, as will combined units for multiband operation in a single control, similar to the TFM-550 and TFM-500 in their phase-two development. Users with a TFM-138 can simply remove their old Dzus-mounted unit, and drop in a new one to achieve full VHF P25 functionality and fully agile frequency control and operator programming in flight.

The tradeoffs of the Technisonic approach are that only VHF coverage can be delivered at the moment, and only single radio control currently is possible in that 3-inch-by-5.25-inch panel space, which can be a problem in crowded cockpits.

These systems have been shipping since late in 2000, with the U.S. government buying systems in quantity. Full DO-160D environmental compliance has already been obtained (plus supplemental approval to the stricter DO-160C Part 21/Cat. Z), along with U.S. Federal Communications Commission (FCC) and Industry Canada approval.

Technisonic is developing additional bands for release next year, to extend coverage all the way to 800-900MHz.

Subtle Differences

Channel programming and the possible permutations of what can occur on a radio channel under P25 architecture can be confusing. Using these new modes adds some learning time for both users and installers, an important issue to address carefully for successful implementation.

The current Motorola P-25 technology used by NAT and Wulfsberg supports multimode reception on a specific frequency, but responds only in it's current preprogrammed mode (analog, digital, wide band, narrow band, etc.) for that channel. The Technisonic P25 technology supports multimode reception on any frequency and also the optional multimode automatic response in the correct matching mode without user rechanneling. These subtle operating differences can affect the comparison of channel storage and functionality between systems.

Each manufacturer's avenue to reach a workable P25 communication solution is built on some solid proven hardware in the airframe. So users can be reasonably confident that the transition has some good history to build on. Selecting the best approach is a difficult decision.

My thanks to Ray Lewis at Northern Airborne Technology, Scott Hovelsrud at Wulfsberg, and Brian Conrad at Technisonic for providing detailed information on their systems and helping Avionics Magazine readers with their P25 system planning.

Walter Shawlee 2 may be reached by e-mail at

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