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 PSR-500/600 Getting the most out of Multisite
Solution The PSR-500 and PSR-600 scanners include a special "MultiSite" functionality that enhances operation on Motorola and P25 trunked radio systems that utilize multiple networked sites to cover a large geographic area.

To understand how MultiSite works, it is important to make the distinction between "simulcast systems" and "networked" systems. Both types of systems have multiple sites, but they are quite different in how they operate.

A simulcast system utilizes two or more sites, up to 15 depending on the technology. Each site is exactly the same in terms of number of transmitters and the frequencies that are used. When a channel is assigned to a voice call by the trunking system controller, the assigned frequency transmits the call from every site in the system simultaneously, providing simultaneous multi-site coverage to the service area.

A multicast system utilizes two or more sites, up to very many sites, for example, in statewide systems. Unlike simulcast, the exact same frequencies are not utilized at each site. The sites operate independently of each other, relying on the trunking system controller to keep track of where various subscriber radios are in the network, and assigning calls to the necessary sites as users roam in and out of the coverage footprints for sites in the network. In multicast systems, a "site" can be a single RF tower site with its own set of frequencies, or, a simulcast "cell" that has multiple sites with the same frequencies, as described above. In a multicast system, a simulcast cell is treated as just another single site, even though the simulcast cell will have more than one site.

MultiSite is an advanced user concept that requires some experimentation, and even then, due to location, variability and system designs, not all users will be happy with the results for a given system or location within that system, and may be better off not using the feature and programming/selecting the desired site manually.

MultiSite "Roam" is used when you want the radio to automatically find and use the best available site as you move around in the service area of the system. The trick to getting good performance from MultiSite Roam is to optimize the Threshold Hi and Threshold Lo values on an individual basis for each networked site. You'll want to use the Analyze function to study the CC quality numbers that you see for your system, then set Threshold Hi to correspond with the CC value that you consider to be the minimum for good performance. Set Hi too high, and your radio will never find the system.

Then, you should set Threshold Lo to correspond with the value where you want the radio to give up on the current site and start looking for another site (which, of course, must have a decode quality that exceeds the Threshold Hi number that you set earlier in order for the radio to find and use the new site).

MultiSite "Stat" is used when your location is more or less fixed, and you wish to monitor traffic on any site that is within range of your location. With MultiSite Stat, the radio will sample each control channel in the TSYS control channel list to see if trunking control data is present. If trunking control data is present, the radio will sample the control channel momentarily, and play any voice calls that match programmed TGRPs or Wildcard objects for that system. Most users will probably find that the MultiSite feature works very well once it is optimized properly. If you are not satisfied with the performance of MultiSite after you optimize the Threshold Hi and Threshold Lo values, for example, you feel that you are missing too many calls, consider programming the sites individually, and not using MultiSite to track the system.

Article Details
Article ID: 9
Created On: 07 Nov 2007 12:17 AM

Posted By: Tim Begnaud On: 09 Nov 2007 11:07 PM
I have used the multisite roam feature on the new State of LA Motorola 700 MHz digital trunking system. I recently took the scanner on a trip that covered 310 miles across the state. The scanner performed flawlessly when tracking the system and switching sites as I travelled. I had good coverage on about 95% of the route. I have the threshold low set to 80% and the threshold high set to 95%. I have audio boost set across the board on everything in the scanner so that I can hear all transmission above the road noise while going 70 MPH on the interstate. With the audio boost on I can hear all transmissions without a problem.
Posted By: Andrew On: 13 Nov 2007 08:49 AM
I'm still trying to figure out why it says that the lo value should exceed the hi value... It sounds like they are switched or something.
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