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PeterO
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Misconceptions about WiFi Antenna

Wed Apr 05, 2017 10:19 am

jahboater wrote:Wifi radio is a two way thing. If you increase the transmit power, the other side may hear you better. But unless the other side also increases their transmit power, you will not hear them and it still wont work.
Best to improve the antenna which increases both the transmit radiated power and the received signal strength.
Harder, would be to change the antenna's radiation pattern (focus it into a beam for example) which would improve the communication and at the same time reject other interfering users on the same channel.
There are several things wrong with those statements.

Changing the antenna does not "increases the transmit radiated power", the antenna is passive, only an amplifier can increase the transmitted power. It might increase the Effective Isotropic Radiate Power (eirp) but that is not the same thing ! Also, if you change to an antenna with more gain you might have to decrease your transmitter output power to keep below the maximum allowable eirp. (eirp = tx power x antenna gain).

If an antenna does have "gain" it is precisely because it has a "changed radiation pattern", which might (as you say) focus the radiation into a beam, or maybe it just squashes the pattern to send less of the radiation vertically upwards (which is probably not a useful direction unless you are making a TV advert with a man hanging from a helicopter!).

An antenna that is directional can only decrease interference from other users on the same channel IF they are not in the same direction as the wanted signals otherwise they will be enhanced by the antenna along with the wanted signals.

PeterO
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jahboater
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Re: Misconceptions about WiFi Antenna

Wed Apr 05, 2017 10:34 am

PeterO wrote: There are several things wrong with those statements.

Changing the antenna does not "increases the transmit radiated power", the antenna is passive, only an amplifier can increase the transmitted power.
It might increase the Effective Isotropic Radiate Power (eirp) but that is not the same thing ! Also, if you change to an antenna with more gain you might have to decrease your transmitter output power to keep below the maximum allowable eirp. (eirp = tx power x antenna gain).
I know all that, I was just trying to keep it simple. By "transmit radiated power" I meant ERP and considered using that term, but decided not to as it was straying off topic or too much detail. In the context of the original post it was not necessary.
PeterO wrote:If an antenna does have "gain" it is precisely because it has a "changed radiation pattern", which might (as you say) focus the radiation into a beam, or maybe it just squashes the pattern to send less of the radiation vertically upwards (which is probably not a useful direction unless you are making a TV advert with a man hanging from a helicopter!).

An antenna that is directional can only decrease interference from other users on the same channel IF they are not in the same direction as the wanted signals otherwise they will be enhanced by the antenna along with the wanted signals.
Agreed, and of course all that is true, but I did not want to present a lecture on antenna theory! I was trying to sum it up in just a few words.

I believe the gist of what I said was correct - increasing transmitter power alone is usually not the answer. A well chosen antenna is the best answer.

M0JNX
(which is probably not a useful direction unless you are making a TV advert with a man hanging from a helicopter!).
I am reminded of the antenna's I keep seeing on speed boats. Often 2x5/8 and raked backwards to look cool! Of course much of the radiation goes into the water and the other side into space.

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PeterO
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Re: Misconceptions about WiFi Antenna

Wed Apr 05, 2017 10:48 am

jahboater wrote: I know all that, I was just trying to keep it simple.
Next time preface your "keeping it simple" explanation with words to that effect, otherwise it looks like you don't know what you're talking about :roll:
PeterO
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jamesh
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Re: Misconceptions about WiFi Antenna

Wed Apr 05, 2017 7:37 pm

Watch out, HAMS about....

KN08BY


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