Your questions answered: choosing the best Roaming RSSI level

In my post on the radio's roaming RSSI, I gave some ideas on how to set this value, to achieve the best possible user experience, on a IP Site Connect or Linked Capacity Plus system. But how does one determine the optimal RSSI threshold?

There are a few methods:

Method A: Thumb-suck. Otherwise known as trial and error. This generally has a success rate of around 50% and involves entering a value that seems reasonable then trying it out.

Method B: Looking at coverage plots. For ease of representation - and to help explain this - I've drawn three oversimplified coverage plots. In reality, a coverage plot will look something like this.
In the above plot, the coverage from the two sites intersects at -100dBm (within the black rectangle).
In the below plot, this is around -80dBm.
And in this one (below) the RSSI from the three sites intersect at -70dBm.

Method C: Drive testing. The MOTOTRBO Site Survey Tool allows you to a) connect a MOTOTRBO GPS model radio to a PC and record the coordinates and RSSI, in a file that can be plotted on a map or b) record the RSSI and GPS coordinates, of all radios transmitting on a specific repeater, via an IP connection. A real coverage map can therefore be created which gives the most accurate result.

Read more about Roaming RSSI in IPSC here and in LCP here.

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