Motorola trunking refers to a proprietary trunking protocol created by Motorola so, to be clear, this page talks about the format, not the vendor for which it is named. Monitoring of Motorola trunking systems is mostly straight-forward. Here are some hints to help understand behavior unique to Motorola systems.
Motorola uses channel numbers to tell its radios which voice channel to listen or transmit. Frequencies can be calculated from these channel numbers using a table of formulas known as a band plan. The formula is simple enough. Each table entry is low channel, high channel, base frequency, and step. The formula is Frequency = Step * (channel - low) + Base for any channel number that falls between low and high. Motorola systems on 935 Mhz use one standard band plan. On 851 Mhz, there are five or so standard band plans with "Standard", "Splinter" and "Rebanded" being the most common. The band wizard can be used to quickly adjust a site's band plan. On a networked system, it is possible to two sites to use different band plans. For VHF and UHF systems (frequencies below 512 Mhz), there is no standard band plan. You'll have to use some algebra and a little trial and error to figure a band plan.
Motorola group and radio IDs are displayed as 16 bit numbers. You have several options for display of these IDs as decimal, hexadecimal, modern, and Motorola format. In Motorola format, group IDs start with an '8' and radio IDs start with a '7'. In decimal format, the ID appears in the range of 0 to 65535. ID number 65536 is used to indicate a BSI or base station identification event on a voice channel. It's not an actual call or group ID. You may hear a morse coded station ID on the affected voice channel. Hexadecimal format has the advantage of being more compact since a full ID is only 4 digits in the range of 0000 to FFFF (or 000 to FFF for group IDs in Modern format).
Beware that talkgroups are displayed as 16 bit numbers (in decimal and hexadecimal formats). They're actually 12 bit numbers. The value you see is the actual talkgroup multiplied by 16. Talkgroups are displayed this way for historical reasons related to compatibility across Type 1 systems. The format makes spotting the relationship between a Type 1 radio ID and Type 1 talkgroup very easy. If you choose either Modern format, Type 2 group IDs are displayed without being multiplied by 16. The Radio Reference DB displays Motorola talkgroups in decimal and modern hexadecimal format.
Type 1 radio IDs have a mathematical relationship to their corresponding group ID. In most cases, the system need only broadcast one ID to indicate both the transmitting party's radio ID and the audience group ID. This relationship is determined by a fleet map. More on that below. If the Motorola system you monitor is not in the 851 to 869 Mhz range, it is Type 2. Type 1 and mixed Type 1/2 systems (with their associated ambiguities) exist only on 800 Mhz systems.
Type 2 radio IDs and group IDs have no mathematical relationship to each other. Any radio ID can potentially listen to or talk on any group ID.
Type 2i systems, also called Hybrid systems, operate a mix of Type 1 and Type 2 radios.
Talkgroups are organized into eight blocks. The number of radios addressed by a single Type 1 talkgroup is determined by a sizecode. The minimum is 16 for sizecode 'A' but can be as large as 4096 for sizecode 'Q'. See this document for reference. You can edit the sizecode on the system's info tab. Look for the "Fleet" property. A sizecode entry of '?' means the sizecode is unknown. A sizecode entry of '1' means the block is definitely Type 1 but the exact Type 1 code (a letter from A to Q) is unknown. A sizecode of "2" indicates a Type 2 block. A Hybrid system may have a mix of 1's, 2's and letters. A pure Type 1 system will have no 2's. A pure Type 2 system will only have 2's in each block.
On the Radio Reference Database, you can see the fleet map next to the system ID. Determining the appropriate size code for a fleetmap involves some guesswork. It boils down this: when two different Type 1 radios talk, are they talking to each other? By listening, you can form an opinion and adjust the size code so that these two radios fit in the same group - or different groups. If you discover a size code not in the database (or one that needs changing), please make a submission.
If you're still reading, you know how Type 1 vs. Type 2 dictate group and user ID addressing. Both have a system ID and Connect Tone which are very useful for positively identifying a system and reporting it to the RR DB. Type 2 systems can be further categoried by network capabilities. SmartZone systems have a site number. A site with no site number is displayed as having site number 0. Such sites are called Island sites. They have no peers. Some SmartZone systems advertise a site number (1 to 64) but have no peer or neighbor sites. Most SmartZone systems will have multiple peer sites - as displayed on the Peers tab of the Site window.
Very large SmartZone networks will span two or more system IDs. These are called OmniLink. Unitrunker uses the peer information broadcast by such sites to determine whether two systems are part of the same network and will automatically delegate one system to another so that group and user information is shared.
If you monitor a site on an Omnlink system where all adjacent sites have the same system ID, the program won't report the system to be OmniLink.
In rare cases, you may come across two Motorola systems with overlapping coverage that use non-overlapping group and radio IDs. For example, a public safety system and a public works system in which the group and radio IDs have been coordinated. This allows the public safery users to switch to the the public works system in case of equipment failure. You can use the manual Delegate feature to link these two systems together. If and when such a failure occurs, your group and radio labels are already shared between the two systems.
Beware of using a Uniden model scanner for inline decoding. The "X" and "XT" models may pass bad data without indicating such to the decoding application. The result is garbage in, garbage out. If you plan to do extensive decoding of Motorola, use discriminator audio. This issue is only for decoding Motorola. EDACS, LTR, and P25 decoding are fine. Also, this is NOT a problem with the Uniden HP-1 which passes discriminator audio directly over the attached USB cable.