1. Wifi antenna receiving power

I have 2.4GHz wifi that transmits at 100mW, I have another antenna 1 meter away from its transmitting antenna, how much power can I receive with this receiving antenna?

The amount of power that can be received by an antenna depends on multiple factors, such as the distance between the antennas, the frequency of the signal, and the gains of the transmitting and receiving antennas. It's also influenced by environmental factors, such as interference and physical obstructions. The formula that is often used to calculate the received power in free space (assuming line of sight and no interference) is the Friis Transmission Equation:

Pr = Pt + Gt + Gr + 20log10(λ/4πd)

where:

    • Pr is the received power (in dBm)

    • Pt is the transmitted power (in dBm)

    • Gt is the gain of the transmitting antenna (in dBi)

    • Gr is the gain of the receiving antenna (in dBi)

    • λ is the wavelength (in meters)

    • d is the distance between the antennas (in meters)

You have a 2.4GHz Wifi that transmits at 100mW, which is 20dBm (10log10(100)). You haven't specified the gains of the antennas, so let's assume they are ideal isotropic antennas which do not favor any direction and hence, have 0 dBi gain.

The frequency is 2.4GHz, so the wavelength (λ) can be calculated using the speed of light (c) formula, λ = c/f. The speed of light is approximately 310^8 meters per second and the frequency is 2.410^9 Hz, so the wavelength is approximately 0.125 meters.

Your antennas are 1 meter apart, so d = 1 meter.

Substitute these values into the Friis Transmission Equation:

Pr = 20dBm + 0dBi + 0dBi + 20log10(0.125/4π*1) = 20dBm - 47.55dB = -27.55dBm

So, the received power would be around -27.55dBm if we're only considering free space path loss and assuming ideal conditions, which might not be the case in a real-world scenario due to factors like obstructions, antenna patterns, interference, and other complexities of radio wave propagation. The power in mW can be found by reversing the dBm conversion: Power (in mW) = 10^(Pr/10) = 0.0018 mW approximately.

This is a theoretical calculation and in a practical scenario, you may receive more or less power depending on the aforementioned factors. Also note that your receiver should be capable enough to receive such low power levels.

TLDR; 1 meter away from wifi accesspoint you can harvest in the order of 1.8 microwatts