Does a P25 tower act as a repeater?

[hruskacha]

I have an 800MHz P25 Simulcast site nearby and I was deciding if a directional antenna would be a good idea for my stationary scanner.
It would make sense for improving Control Channel and Alternate Control Channel's signal, but if I'm not mistaken, the P25 radios don't talk back through the towers, they just broadcast on the frequency selected by the control channel? The site has 3 antennas on the tower, which would correlate to the 3 Control Channels for my Counties Simulcast System.

 

[62Truck]

The P25 radios do talk back through the towers. Just aim a yagi at the nearest site and that may help you with simulcast issues. The number of antennas does not correlate to the number of control channels.

Some sites may use multiple transmit and receive antenna depending on a few different things, they will go through a cominber system to multiple transmitters and receivers. Depending on a few other factors these antennas maybe omni directional, or directional, and this will also factor in how many antennas maybe needed and where they are placed on the tower.

 

[wa8pyr]

I have an 800MHz P25 Simulcast site nearby and I was deciding if a directional antenna would be a good idea for my stationary scanner.
It would make sense for improving Control Channel and Alternate Control Channel's signal, but if I'm not mistaken, the P25 radios don't talk back through the towers, they just broadcast on the frequency selected by the control channel? The site has 3 antennas on the tower, which would correlate to the 3 Control Channels for my Counties Simulcast System.

Yes, they are repeaters, and yes, the P25 radios do talk through the towers.

The reason you're only seeing three antennas is because there is a receiver multicoupler and transmit combiner(s) in use inside the shelter

All of the receivers are sharing one antenna via a receive multicoupler, which probably has a tower-top preamp (look for a box mounted near one of the antennas).

The other two are used for the transmitters; a typical installation has up to ten transmitters per antenna (the number depends on TX power and some other variables), so it's probable that there are at least ten and maybe up to twenty repeaters at the site.

However, of all those multiple channels at a tower, only one is acting as a control channel at any given time; the rest are assigned as voice channels by the system controller.

In a simulcast situation, all of the sites are identical and sending the same stuff on the same channels at the same time, so a directional antenna may help if you're using a scanner that doesn't handle simulcast very well.

 

[wgbecks]

Although P25 trunking systems operate with primary and alternate control channels at each site, they essentially consist of a number of P25 repeaters under control of the site and system controllers. Therefore, all voice channel traffic associated with a particular site and it's control channel will all transmit from the same tower on the system assigned frequency (repeater) or voice trunk.

This does not mean to imply that the same voice calls will not broadcast on other sites in the system. In the case of as simulcast system, all radio frequencies are duplicated and transmit simultaneously from all sites within the simulcast cluster. Conversely, on SmartZone systems, it will depend upon what sites other members of the same talk groups are affiliated with for the system controller to direct or multicast said voice traffic out on other towers (sites) in the system.