April 15, 2005
by John Dickens
P 25 Radios
They are on the way...
One of the big problems that occur in emergencies is the inability of responders from different agencies to communicate with each other. This is known as the lack of interoperability. This has been a huge issue! Recent events like the 9/ 11/01 World Trade Center disaster have shown that this is still a problem and can cost lives.
In 1989 the Association of Public Safety Communications Officials International (APCO), the National Association of State Telecommunication Directors (NASTD) and the National Communication System (NCS) established Project 25 (P25) to address the problem of interoperability as well as make better use of scarce radio frequencies. Representatives from Federal, State, and local governments began an effort to develop a set of common technical standards for land mobile radio systems. An additional benefit of a common standard would allow any number of manufactures to produce compatible equipment. thus increasing competition and lowering prices. P25 promised to avoid locking customers into a proprietary system from a single manufacturer.
P25 radios must be able to operate the old way, in analog mode on 25 kHz channels. This is called backward compatibility, and allows agencies to gradually transition to digital while continuing to use older equipment, like VHF marine band radios. This is very important for areas like ours.
At present most public safety channels are 25 kHz wide. Current P25 radios are designed to use 12.5kHz wide channels allowing two conversations to take place where only one used to fit. This is called "narrow banding." Eventually P25 radios will use 6.25 kHz wide channels allowing four times as many conversations compared to the old analog way.
P25 radio transmissions may be encrypted and they are frequency agile, they can carry voice or data and can operate up to 9600 bits per second (bps). P25 uses a specific method of digitized voice called Improved Multi-Band Excitation (IMBE). IMBE is optimized for human speech.
The P25 radio standard is very technical and is over 1800 pages long. All public safety radios purchased with federal funding must be P25 level. If you or your village buys radios for public safety, you need to make sure they are P25 compliant.
Emergency Medical Services / Injury Control
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