Radio Shack PRO-90 owner manual Trunk Tracking, Types Of Trunking Systems

20-520.fm Page 32 Wednesday, August 4, 1999 3:06 PM

TRUNK TRACKING

Your scanner is designed to track transmissions on Mo- torola Type I, Type II, and hybrid analog trunking sys- tems, which are extensively used in 800 MHz communications. Remember these important points when tracking transmissions:

•Your scanner monitors Type II systems by default. However, you can change this if the system in your area is different (see “Types of Trunking Systems” below and “Scanning Type I and Hybrid Trunked Systems” on Page 44 for more information).

•Your scanner cannot track transmissions on non- Motorola trunking systems.

•Your scanner cannot track an 800 MHz trunked sys- tem and scan frequencies in conventional mode at the same time.

•The frequencies for many of the 800 MHz public safety systems are listed in the separate “National Public Safety Trunked System Frequency Guide” included with your PRO-90.

TYPES OF TRUNKING SYSTEMS

Your trunk tracking scanner can monitor two basic types of systems — Type I and Type II. Instead of selecting a specific frequency to transmit on, a trunked system chooses one of several frequencies in a 2-way radio us- er’s talk group when that user presses PTT (push to talk). Thus, trunking systems allocate a few frequencies among many different users, but the way Type I and Type II systems do this is slightly different. One important distinction between these systems is the amount of data transmitted by each radio when its push-to-talk button (PTT) is pressed. In a Type I system, the radio’s ID and its current affiliation (the trunk system it belongs to) are both transmitted. In a Type II system, only the radio’s ID is transmitted.

Why the difference? In Type I systems, each radio in the trunk group individually transmits its own affiliation, while the trunk system maintains a database that determines each radio's affiliation(s) in Type II systems.

Another difference between the systems is that Type I systems are arranged in a fleet-subfleet hierarchy. For example, it is possible for a city using a Type I system to designate 4 fleets, each with 8 subfleets.

32