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I'm having difficulty understanding how the gain of an antenna works. I appreciate that the gain effectively concentrates the available RF energy into a narrower beam but i can't fathom how this seems to mean that if i have a transmitter transmitting at say 100dBm that i can use antenna gain to produce a power higher than this at a receiver. How is this possible to seemingly 'create' power?

If i supply an isotropic antenna with 40W of power then this theoretically will be dissipated equally in all direction so at any point away fom this i will receive a fraction of this. If i conentrate the energy by beam forming then surely the most i can expect to get is no more than the original 40W.

Also, when we say that the power at a certain point from the transmitter is XdBm what does this mean? i.e. surely it depends on the size of the receiver at that point so you can't make a general statement that at that point the power is XdBm????

Thanks in advance

Beckett

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# Power and gain in antennae

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