WHAT IS P25 OR APCO 25 RADIO STANDARD?
Project 25 (P25 or APCO-25) is a digital voice mode designed to meet the high demands of public safety and public works dispatch radio systems. This mode has long been used in Amateur Radio and there is growing interest to use P25 amateur repeaters.
The P25 digital mode like other digital modes uses a vocoder with a specific codec to convert audio to data. Think of it like music audio on a CD. The CD has packets of audio data that is decoded into music. P25 is (data) voice packets.
It is the standard digital mode for police, fire, EMS, and public works because its vocoder codec provides the best audio correction and voice rendering. This means better audio fidelity and the correction of voice packets on the fringe of coverage will be more reliable and readable.
WHAT DOES P25 SOUND LIKE?
P25 has very similar audio qualty to a CDMA cellphone call, the advatage to this is when your signal is noisy in analog P25 has the potential to come thru crisp and clear. On the flip side listening to a P25 signal in analog sounds allmost like buzzing – hash static noise. Keeping that in mind thats why we recomend using PL decode on SVRG systems that have P25 capability. Below is are a few examples of what P25 sounds like to an analog user and a digital user.
This is an audio clip of P25 audio on the Salinas Valley Repeater Group.
This is an audio clip of P25 when listening with an analog only radio.
WHAT RADIOS CAN I USE?
There are several models of radios you can use. While there is a rumor that P25 equipment costs a lot, this is far from the truth. Yes there are radio models that costs upward of several thousand dollars but, it is not necessary to use these radios if your budget is limited. There is plenty of used public safety radios that were used in the early to mid 1990s and 2000’s. These include the Motorola XTS and XTL series, astro saber or spectra series, and other brands such as Bendix King, Kenwood and ICOM. ICOM makes a P25 radio that costs about the same price as a top tier legacy portable ham radio. We recommend purchasing a radio that has FPP or front panel programming enabled as this will allow you to program frequencies, PL tones, DCS tones, and NAC codes from the front panel without software.
Some radios have other P25 features such as TXT messaging, station ID, paging, location & elevation / distance and from the person your talking to.
HOW IS P25, DMR, NEXEDGE AND (EUROPEAN) TETRA SIMILAR AND DIFFERENT?
They are similar in a sense that they are digital modes that use a vocoder to convert audio into digital packets. However, the codec on the vocoder are different between the many modes. P25 is the only fully interoperable codec between all manufactures. All other digital modes are limited to one or two manufactures. P25 codec provides better error correction on the fringe of coverage and also provides a better audio quality that most would describe as very vibrant true voice. DMR on the other hand has lower true voice fidelity than P25. Therefore P25 is the preferred codec for this system.
WHAT SYSTEMS ARE CURRENTLY LINKED AND OPERATING IN MIXED MODE P25 ON SVRG?
Currently we have 5 systems linked and operating mixed mode analog and P25. The system serves analog or digitial on a first come first serve basis. All systems use a NAC code of $293 for P25.
The Salinas Valley Repeater Group also keeps an alias database of all MDC/ASTRO PTT IDs. A new user that is interested in operating on P25 and using MDC on analog is encouraged to request a PTT ID. This data base is stored on a google doc and will be made availble to each person that requests and ID. The user can then populate the unified call list on their radio and alias the ID with the corrisponding call sign of the station.
