For this and all subsequent examples, assume the impedance is 75 ohms.įigure 1. Consider the example in Figure 1, which shows a single RF signal whose power is +20 dBmV. ![]() It’s of concern because excessive total power is what overdrives lasers, set-tops, modems, and other devices.”Ĭalculating total power does require some number crunching, since you can’t simply add the individual signal levels in dBmV to get total power. For more on the latter, see my Summer 2017 Broadband Library article “The Wise and Mighty Decibel,” available on-line at Total powerĪs I noted in the Summer 2017 article, “Total power is the combined power of all signals in a given frequency range - for instance, the downstream. The second reason we use dBmV is because that metric expresses power in terms of voltage. Working in the world of the decibel (dB) makes dealing with very small and very large numbers much easier. For example, 0 dBmV is only 13.33 nanowatts (~13 billionths of a watt!). The first reason is the typical power levels we deal with are very small. You might wonder why decibel millivolt (dBmV) is used instead of watt (W) for RF power in cable networks. Quick side note: When we measure RF signal level we are measuring RF power. ![]() We’re going to look at these two parameters a little more closely. Grab a cup of coffee and a scientific calculator. Two RF power-related parameters that can cause confusion are total power (also called total composite power) and power spectral density (PSD).
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