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. And your noise should be higher than -90.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. You normally like to see your signal no higher than -67 for voice or -76 for data. Next to the speaker, you are showing say -30dBm but your noise may be like -70dBm. The lower the noise dB the louder the noise is. Noise, we dont want to be loud, so we want to see noise at -100. ![]() ![]() If you are right under the ap you will get like a -30ish. You will see -59 of signal is good, in fact I am about 50 feet from the AP. But check your ap, becuase you may have the option to change it to dB. Vendors sometimes give you a % or dB scale when grading the signal.You really cant make headers or tails from the % scale becuase each vendor has different % measurements. This is an exmaple of a loud signal but poor quality.Īs for measuring the signal and noise or should we say quality of signal. The sounds is so loud you cant hear anything but screaming. Suppose for a minute you are front row at a rock concert right next to the speakers. ![]() ![]() First, lets look at the concept of signal quality and strength.
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