WRt32x Antenna question: Antenna Gain

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weaklinks
DD-WRT Novice


Joined: 06 Oct 2019
Posts: 37

PostPosted: Fri May 01, 2020 11:57    Post subject: WRt32x Antenna question: Antenna Gain Reply with quote
Hello,

I purchased from Amazon TECHTOO 9dBi Omni WiFi Antenna with RP-SMA Connector for Wireless Network. Should I leave the antenna gain section alone or do I need to make adjustments I know the transmit power we cannot change because FCC. How about the Antenna Gain that has default 0 in it. Also if anyone has the best settings for Wirless to optimize. thank youu
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SurprisedItWorks
DD-WRT Guru


Joined: 04 Aug 2018
Posts: 927
Location: Appalachian mountains, USA

PostPosted: Sat May 02, 2020 19:23    Post subject: Re: WRt32x Attena question Antenna Gain Reply with quote
weaklinks wrote:
Hello,

I purchased from Amazon TECHTOO 9dBi Omni WiFi Antenna with RP-SMA Connector for Wireless Network. Should I leave the antenna gain section alone or do I need to make adjustments I know the transmit power we cannot change because FCC. How about the Antenna Gain that has default 0 in it. Also if anyone has the best settings for Wirless to optimize. thank youu

For the last dozen or so years, most of my professional life has been as an antenna engineer, so I'll take a stab at this one. I can't actually imagine why dd-wrt has a setting for this. It's a matter of antenna design. Nothing dd-wrt can really do about it. (Or is there something going on here that is seriously nonobvious. Anyone?)

BTW, an antenna is not an amplifier, so it cannot produce more transmit power. All it can do is redistribute the power given to it by the transmitter across the sphere of possible directions of radiation. The "i" in "dBi" is for "isotropic." An isotropic antenna is hypothetical thing that distributes the power uniformly across all those directions, and an antenna with 9 dBi gain is producing, in some direction or directions of interest, a power density 9 dB above what an isotropic antenna would produce. That's a power ratio of roughly 8:1. The simplest (not terribly realistic, but if we want simple) model of what's happening is that power is being radiated at equal levels across 1/8 of the sphere and not radiated at all across the other 7/8. So imagine a sphere with the top and bottom chopped off so that only 1/8 of the original surface remains, now in a sort of donut shape. That's your omni pattern.

The takeaway is that you get your gain in one direction by not radiating it somewhere else. In this case, if everything is on one floor of the house, things may be great. If a client is upstairs two levels above the router, it may not fall into the donut and so may receive a significantly lower power level (not actually zero, as real antennas don't go from all to nothing in an abrupt way). So if you need decent coverage in lots of directions that include directions significantly upward and downward, be careful about going with a high-gain antenna. High gain in one direction means low gain (negative number of dBi) in another direction, and a really high-gain omni antenna has a really flat donut. It's not friendly towards clients up or down from the horizontal plane (assuming the antenna is oriented vertically).

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