 Hi, I'm Thomas Houdar of Elements and in today's Inside Wireless episode we'll talk about the dependence of the output power and the MCS index the radio is working with. Before we start or like, comment and consider subscribing to our channel and we'll notify you when never release a new video. Did you ever wonder why radio manufacturers recommend using lower output power to hire the MCS index you use? Put aside the regulation rules, the reason is the radio hardware itself, namely the amplifier. Amplifier is the part of the radio that increases the power of the signal fed to it. A small signal at the input of the amplifier turns into a stronger one at its output. This can be illustrated on an XY plot, on the X axis is the input signal power and on the Y axis is the output signal power. Ideally, the amplifier works in our linear regime depicted as a line. As we bring a signal of a certain power to the amplifier gate, we get the signal with the same shape but higher power at its output. In reality, the amplifier is linear only for a limited span of input powers. At some point, the line starts bending into a curve. Here we say that the amplifier is already in a non-linear regime. So if the input signal power lies in the non-linear part of the curve, the output signal is still amplified but its shape will be distorted. This distortion can be viewed as a form of a noise added to the signal. The WISP radios use quantum modulation to encode information onto an RF wave. The higher the depth of the modulation, or the MCS index, the higher the required SNR. For detailed explanation on this topic, check out our previous video on quantum modulation by clicking the link in the corner or in the video description. Based on the growing demand on the signal SNR with growing MCS rates, we need the amplifier to work in the linear regime if we want to use high MCS rates. Because low MCS rates can work with lower SNR, the added noise due to the amplifier non-linearity is not fatal to the successful data transfer so the output power can be high. On the contrary, higher MCS rates require increasing SNR levels. Here, if we try to use high output power for high MCS rates, the added noise due to the amplifier non-linearity can increase the error rate of the data transfer beyond acceptable level. This is exactly why radio manufacturers recommend using lower output power to higher the MCS rate you use. If you enjoyed this video, consider subscribing to our channel and stay tuned to our social media for more interesting videos from RF World.