Received Signal Strength Indication (RSSI)

Many SCADA radios and even some cellular modems have a Received Signal Strength Indication (RSSI) as one of their diagnostic parameters. It's a good thing, too, considering how important RSSI is. RSSI is basically a measurement of how well the radio is receiving or 'hearing' data. It's typically measured in -dBm, which is the power ratio in decibel (dB) of the measured power referenced to one milliwatt (mW). The general rule is that the closer you get to zero, the better. In other words, -70 dBm is better than -80 dBm and so on. However, the closer you get to zero, the more the front end of the receiver can get overloaded. Imagine someone standing next to you and screaming in your ear. You could certainly hear them, but you wouldn't be able to understand a word they were saying. Same thing with radio. When people (and you know who you are) start putting on power amplifiers and huge gain antennas, you are going to cause problems with your system!

Personally, I like to shoot for right in between -60 and -70 dBm. It's a good, solid signal without being overwhelming to the receiver.

Here's a good reference for RSSI and how it relates to reliability:

§-100 dBm

–50% reliability; fading may cause frequent data loss

§-90 dBm

–90% reliability; fading may cause occasional data loss

§-80 dBm

–99% reliability; reasonable tolerance to most fading

§-70 dBm

–99.9% reliability; high tolerance to fading