8/22/2023 0 Comments Wifi signal strength meter![]() It's definitely possible to design a radio that can handle signals above -30dBm, but not all vendors bother, and exceedingly few vendors publish the max RSSI their radio designs can handle. I would suspect that -28dBm RSSI could be too much for your Mac's Wi-Fi radio front end, and might result in lower throughput than you would get if you moved your Mac farther away from the AP. I've worked with plenty of Wi-Fi radios that hit distortion above -40dBm. 30dBm to -99dBm is much easier to write, and gives us all the range and precision we need with just two significant digits.īy the way, it's possible for a signal to be too strong for a receiver, and overload the receiver's "front end" circuitry, causing distortion that hinders communication speeds (imagine someone shouting in your ear so loud it makes your eardrum rattle). That's a lot of zeroes to type, which is why we go logarithmic and use decibels. So the typical range of power levels you need to talk about with Wi-Fi is 1,000 mW to 0.000,000,000,1 mW. Well-designed Wi-Fi radios can be sensitive to almost -100dBm, which is just 100 femtowatts (milli > micro > nano > pico > femto). In contrast, 1 milliwatt is a known quantity that is independent of regulations and hardware implementations, so we use that. Is 100% the highest power signal the client can handle without distortion? That varies based on receiver designs and modulation schemes in effect. Is 100% the full transmit power of the AP? But that can vary due to regulations, transmitter designs, power saving schemes, and more. Why can't it be a percent? Well, that's mostly because there's no good universal reference points to define as "100%" or "0%". So even if your 802.11 AP (Wi-Fi router) is transmitting at one full watt (30dBm), and you put your client right next to it, you're not likely to see more than 0dBm RSSI on the client. A decent rule of thumb is that any air gap between a transmitter and a receiver, even with efficient antennas right next to each other, is going to be at least a 30dB hit. Regulations vary from region to region, but Wi-Fi devices are often allowed to transmit up to 1 full watt = 1000mW = 30dBm. So a 3dBm signal is roughly 2mW, and a -3dBm signal is roughly 0.5mW. It also works out that every 3dB increase is roughly a doubling, and every 3dB decrease is roughly a halving. ![]() So since 0dBm is 1 milliwatt, 10dBm is 10mW, 20dBm is 100mW, and 30dBm is 1 full watt. Every increase or decrease of 10dB represents an order of magnitude change. RSSI is the "Received Signal Strength Indicator", and it's given in units of "decibels relative to 1 milliwatt", which we abbreviate as "dBm".ĭecibels are a logarithmic scale, which is helpful here because it allows us to compare wildly different power levels without having to write too many digits. ![]()
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