One access points traffic is another access points noise. If you have 2 access points on the same channel for exmaple. So noise should be on the other end, for example -100 to -90. Noise, like signal has a measurement as well. So stuff in the 2,4 or 5 GHz band - that is not 802.11 traffic, right? 85 is much further from the AP.įrom my understanding, noise is ONLY non-802.11 traffic. Signal is how loud a client in this example hears the AP. Or better yet look up a chart online.I guess the 'signal' value, is the signal strength of the 802.11 traffic. Go ahead and count forwards and backwards by three and the math works out.

Everytime you subtract three dB, you have it.

Manipulating the environment utilizing different antennas, power and channel settings, and even the building itself is what we all do for a living.Īs for the number line.everytime you add three dB, you double the power. The trick to designing a system is to figure out how many and where these radios need to go. Obviously, your data and voice will work even better in the 50's or 40's. The closer you get to zero the better your signal will be. There is anywhere between a 25 and 30 dBm difference for voice. There is roughly a 15 to 18dBm difference between the very end of the data and the end of the signal all together. As stated above Cisco recommends at least -72dBm for data and -65dBm for voice. Higher datarates make the noise floor come closer to zero such as -90dBm for 11Mbps (I think.)Īnyway - in order for you to have a good link your signal measurement needs to be at least a pre-determined distance from the noise floor. The noise floor (the drop dead point where there will be no signal at all anymore) of a Cisco radio depending on what data rate etc. The receiver only sees a small portion (thanks dude). Until I saw ScottMac's above post I haven't had the words to explain why. The left side represents the signal strength and the right side represents power. Remember those? Zero in the middle the negative numbers to the left and the positive numbers on the right. instead of a broad azimuth of coverage, the power is concentrated along the Z axis of a narrow beam That is why a yagi antenna or a parabolic dish transmits further than an omni with the same power the radiated pattern is (through some physics tricks) concentrated. The bottom line is that you radiate only so much power from the transmitting system via the antenna, and that power is distributed in a pattern according to the physics of the antenna. the 'power' has dissipated sufficiently that even with an efficient container to catch the 'water,' there is not enough water to fill the cup. If you want to extend the analogy, as you move away from the fountain, the water flow becomes more like rain, with a maximum of.

Your receiver only sees a small portion of the total radiated power, so that's what it reports (also measured in dBm - deciBells relative to one milliwatt). Your AP, with an omni-directional antenna is acting like a fountain it produces a donut-shaped field, 360 degrees in circumference laterally, and ~60-75 degrees vertically (with the antenna vertical relative to the floor) using a total of 17dBm worth of power. 05 Gallon, how much of the water could you catch at any given time? Only a little right? If you stood under a large fountain of water (or a waterfall)that is outputting 50 Gallons-per-second with a coffee cup that can hold. It is because your antenna is putting out a certain level of signal (17dBm - deciBells relative to a milliwatt, one milliwatt) and the receiver is only picking up a percentage of that.

Cisco wifi signal strength dbm