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I have a Wi-Fi access point with six antennas: three for 2.4GHz, and three others for 5GHz. The spec of the access point indicates that the gain is 4 dBi for 2.4GHz antennas, and 6 dBi for 5GHz ones (see the last line on page 2 of the datasheet).

I tried to see what would happen if I replace three antennas by the ones rated 8 dBi (such as these), first replacing the 2.4GHz 4 dBi ones, and then doing the same with the 5GHz 6 dBi ones. During the experiment, I positioned a mobile phone in a different room (on the same floor), and checked the dBm indication with Network Analyzer app. The antennas were positioned to point towards the ceiling.

I expected that once the antennas were replaced, it would make the signal more directional, which means that my neighbors on other floors would receive less of it, while my Wi-Fi devices situated at the same floor would get a stronger signal.

In practice, for 2.4GHz, the signal was just slightly stronger, but not by much: 55 dBm instead of 60 dBm. 5GHz signal was weaker—59 dBm with old antennas, 61 dBm with the new ones.

What could explain that?

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  • \$\begingroup\$ Can you provide a picture or a link to a user's guide or data sheet for the access point? What are these 8dBi antennas you're referring to? And which of the 6 antennas did you replace? \$\endgroup\$
    – SteveSh
    Feb 5, 2021 at 15:47
  • \$\begingroup\$ @SteveSh: I edited my question, providing the missing information. \$\endgroup\$ Feb 5, 2021 at 15:55
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    \$\begingroup\$ You realize that the dBm numbers you quote should be negative i.e. "55 dBm" is actually "-55 dBm" - ditto the others. \$\endgroup\$
    – Andy aka
    Feb 5, 2021 at 16:02
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    \$\begingroup\$ Doing microwave signal strength measurement in a complicated environment like an apartment is like doing circuit measurement with bare copper wires under salt-water. I suggest you start by using the old antennae, walk-test the apartment noting levels, then move the AP a few centimetres and repeat. Then when you see those results, ask yourself whether an expected few dB is even going to be noticeable against the background wildness if you change them. \$\endgroup\$
    – Neil_UK
    Feb 5, 2021 at 16:02
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    \$\begingroup\$ You're using antennas from AliExpress, that says enough. They're cheap and you get cheap results. Do realize that a "proper" antenna with a well defined radiation pattern will be more expensive. Those Ali antennas are usually just a piece of coax cable stripped to a certain length. With some studying and handywork you can make a better antenna yourself. I do not think that would be worth it though. Lining your floor and ceiling with aluminium foil or conductive paint might work much better. \$\endgroup\$ Feb 5, 2021 at 16:02

2 Answers 2

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It is not uncommon to point off-LOS (off Line-Of-Sight) to get the best reception, if there is no visual LOS.

Incidentally, 2.4GHz penetrates walls better than 5GHz, and 5GHz indoor reception strength is therefore even less susceptible to antenna directionality, even though we can expect better outdoor directionality at the higher 5GHz frequency.

Depending on the specific ray-tracing scenario in a deployment, a directional antenna may provide poorer received signal strength and more severe multi-path fading across a WiFi band of, say, 20MHz.

Indoor directionality is applied to keep most of the signal indoors by pointing the antenna generally away from doors, windows and nearby exterior walls, rather than attempting to point them in the direction of the receiver.

As a related case in point, RF uplinks from TV Uplink Vans are highly directional, and in deployments in civic centres (areas with tall office buildings) often the signal is intentionally bounced off the buildings, sometimes taking a few reflections, to work itself out of the built-up area and reach its final free line to the intended satellite receiver.

If you find yourself in one of those tall buildings looking down at such a TV uplink van, take a close look at the direction of the dishes, and hope your office windows are metal coated.

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  • \$\begingroup\$ Because of the power levels involved I highly doubt that those uplinks are going to be bouncing signals off of buildings. \$\endgroup\$
    – SteveSh
    Feb 5, 2021 at 20:10
  • \$\begingroup\$ @SteveSh, you "highly doubt" or you know they don't? \$\endgroup\$
    – P2000
    Feb 5, 2021 at 20:15
  • \$\begingroup\$ Do you really think the FCC or any other regulatory agency is going to allow a microwave signal with an EIRP of over 1 million watts to deliberately irradiate people in a building? \$\endgroup\$
    – SteveSh
    Feb 5, 2021 at 20:18
  • \$\begingroup\$ @SteveSh perhaps you are switching downlink with uplink power limits? \$\endgroup\$
    – P2000
    Feb 5, 2021 at 20:39
  • \$\begingroup\$ I don't think so. A couple of hundred watt transmitter coupled with an antenna gain of 53 dB gets you well over a million watts EIRP. \$\endgroup\$
    – SteveSh
    Feb 5, 2021 at 20:43
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Directional antennas work well for Line of Sight applications (where both Tx and Rx antennas can see each other). If you are indoors it means you will have reflections which will create unpredictable hotspots in gain. My advice is to try moving the access point position to see the variations in received signal. Remember you may have to move it on the same scale as a wavelength at the frequency you are transmitting to see a significant change.

I can see directional antennas for WiFi working well in situations where you need to extend outdoor coverage (like needing WiFi access in a back garden) but not indoors.

Hope that helps.

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