First, lets start with what happens when a radio is first powered up.
As soon as the radio is powered up it scans its list of preprogrammed control channels. If the system is not SmartZone or AMSS then there is a maximum of four control channels (Each site is limited to only four control channels anyway). If AMSS, the maximum is eight, and if SmartZone, the maximum is thirty-two. [I've been told IntelliRepeater sites can have any station act as a control channel, regardless IRs are only used within SmartZone networks and I have yet to see more than four defined. I'm guessing it may occur if all four malfunction.]
Once the control channel is found it will affiliate, but, this depends on whether the radio is programmed to identify on PTT (PTT-ID), or to auto-affiliate. [SmartZone radios will auto-affiliate by default because this is needed for proper site assignment.] It then begins looking for its radio id, its current talkgroup, any talkgroups within the scan list, and the multigroup if one is programmed in. In addition, newer model radios scan for the system id to make sure the radio id is on the proper system. If the radio affiliates to the system, then realizes it is on the wrong system, it will send this error to the control channel, which will echo it out on the outbound side. The radio then will no longer operate on the system (And display Out of Area if equipped). In areas where propagation is good and surrounding areas may use similar control channels (it happens) you will see the error frequently.
One note regarding SmartZone radios:
If the radio is a SmartZone radio it will also look for certain information in the background data sent over the control channel. This includes certain timeout values, connect tones, adjacent site announcements, and alternate control channels. The adjacent site information contains capabilities for the adjacent site, its current control channel, and the site number. There is a maximum of seven adjacent sites to be defined. Each one of these adjacent sites has its control channel sampled by the decoding radio to determine if the radio should switch sites or not. If the radio is a SmartZone OmniLink radio it will do all of the above plus receive an alias name for the current site.SmartZone OmniLink radios can operate on different system ids permitting the system id is included within the adjacent site announcement. If it does switch to the other system id it must be granted approval to roam. The system id is basically considered to be the Zone in a SmartZone OmniLink network. Each Zone has its own Zone Controller with its separate SAC database. When a radio does switch zones it is referred to as trespassing. The current site sends out a site background word specifying if it allows trespassing or not.
Auto-affiliation is preferred because it allows the system manager to properly administer the system. He or she, or anyone who has access to query radio status, will know when that radio is within the network. They will know when it affiliated and to what group. If the network is SmartZone, they will also know what site it affiliated to. Another benefit is when the subscriber chooses to transmit, the radio will only send in its radio id. This allows for faster channel access. If the radio is programmed to only identify on PTT then the talkgroup must be included, I believe, every time. In addition to auto-affiliation, transmission or PTT-ID trunking must also be programmed into the radio so that proper channel access is controlled.
Now our radio is passively watching the OSWs fly by. If it sees a group it is monitoring it will convert the channel hex id to frequency and tune its receiver to that frequency (Trunked radios do not use dual receivers!). Once it arrives on this voice frequency it will look for the proper sub-audible data sent over the voice channel to insure it is on the correct frequency then unmute and pass audio.
Once we wish to place a call, we depress the PTT button, which in turn transmits an ISW containing the talkgroup and radio id (Or just the radio id) on the control channel's input frequency. After transmitting the radio goes back to the control channel (Or rescans if the control channel changed for some reason, which can happen due to a fault) and looks for the call grant. The call grant contains the radio's id and the talkgroup. It then will switch frequencies to the voice channel and begin transmitting. While it transmits it continuously sends in sub-audible data as the connect tone. [I'm not sure but the connect tone may be used for control channel access also.]
If the subscriber's radio has an invalid radio id, the talkgroup or radio id is not allowed at the current site, or has performed an illegal operation, the control channel will notify it on the outbound side. The radio will then tend to emit a bonk, or busy tone, to say "Bad Subscriber!"
When the subscriber has finished talking it will stop transmitting and wait for the disconnect tone on the voice channel's output frequency. Once it receives the disconnect tone it will return to the control channel and enter its passive state.
©2003 Wayne Hayes
To contact me: 2microwave6 -> thebriarpatch.org
05/12/2007
All trademarked names are property of their original owner and are used here for educational purposes only.