RSSI, what the hell is that!

I did consider the title ‘where have my μV gone’ but hey here we are. If you are rich/lucky enough to have an Impres microphone for your shiny new Motorola DM4600 or have a DP3600/4600 etc you may have played with the RSSI function. Received signal strength indicator, an S meter to you and me. The information is presented in dBm, that is decibel relative to 1mW.

Why move away from the traditional μV? Well using a dB scale makes a lot of things easier. For example if you know from experience that your rig can receive a DMR signal with no artifacts at -122dBm but you nearest repeater hovers around the -127dBm mark what aerial gain do you need to receive the repeater? Easy -122-(-127) = 5 so a 5dB gain aerial will sort things out.

Using similar thinking RSSI function can be used to find good spots to access repeaters, check filter tuning and look for noise sources around the shack. The resolution of the RSSI display is much better that a traditional S meter, and way better than that silly green mobile phone signal indicator.

All work, text and images © GB7MB


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