# Amount of power received by a antenna and a tank circuit

#### Drmario5237

Joined Oct 14, 2018
65
Hello. I was wonder if there is any way or formula for the amount of volts and amps a antenna attached to a tank circuit picks up. I know the inverse square law applies here and the gain of the antenna to but what else and if the transmitter is in watts do you need to know the volts and amps of those watts to know how the inverse square laws effects them to get the volts and amps received. Secondly,. Whatever the antenna and tank circuit received in volts and

#### Papabravo

Joined Feb 24, 2006
14,864
A modern communications receiver has the ability to measure signal levels from remote RF sources. For communications purposes, a typical signal might have a power level in the range of -100 dBm to -140 dBm. Weaker signals are barely intelligible and stronger signals tend to be be from nearby sources. In case you are not familiar with dBm as a unit of measurement allow me to explain. It expresses the power level of the incoming signal with respect to a signal with a power level of 1 milliwatt. The minus sign says the power level of the incoming signal has a power level that is less than 1 milliwatt. How much less? Glad you asked. Let's take -100 dBm as an example. Using the formula:

$$P_{dBm}=10*log(\frac{P_L}{0.001})$$

We can see that it is 10 orders of magnitude smaller than 1 milliwatt. That is about 100 femtowatts, where 1 femtowatt is the same as $$10^{-15}$$ watts. There are an infinite number of ways that you can specify a voltage and a current to have this power level. For example if you have 1 μV at 100 nA that would be a power level of 100 femtowatts or -100 dBm. If the voltage was 10μV and 10 nA, that would be the exact same power level. If you graph all of the combinations that have a constant power level you get a hyperbola. Any time you multiply two things together and the answer is a constant, this is what the graph looks like.

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