# Forum

## RF Theory

1 posts by 1 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: March 29, 2008:
• There is more to it than just the antennas!

First, read Ted's post above. He is right on, but since no one really responded to it I want to put it into my own words.

To summarize the Rayleigh-Helmholtz reciprocity theorem, no matter which direction the RF flows, the total gain from the antennas is the same. For example:

2dBi antenna -----> 15dBi antenna = total gain 17dBi
2dBi antenna <----- 15dBi antenna = total gain 17dBi

Now, that's antenna gain. Now on to transmit power.

Summary: The ability to transmit has no bearing on how well you can listen.

If you increase the transmit power of an AP, does that also increase it's receive sensitivity? Nope. So, it is possible to have a device transmit where the receiving device can hear, but the receiving device does not have the transmit power to respond. This is where the "reciprocity" statement is misleading. It is true for antennas, but not true for an entire RF system.

If this isn't clear, please post any questions. I don't want this theorem to be misleading to Wi-Fi folks.

Gene

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