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The problem

There's a concrete wall between my computer and my router (Linksys E900) which affects my WIFI reception pretty harshly, computer receives signal is at -65 dBm, at this rate i get around 5%~8% packet loss. Without the concrete wall blocking the signal i get around -30 dBm to -45 dBm, which results in only about 1% packet loss. (Tested with desktop and laptop).

http://i.imgur.com/AQhodaQ.png

The idea

There's a door in my room, perhaps if I could make my own passive repeater, bending the WIFI's radio wave's path to turn a corner (and go through the door instead of the concrete wall), would my WIFI reception increase significantly?

If this is a good idea, how do I go about making it?

Where do I learn the math on how big the repeater needs to be and how to position it? What materials do I need for this?

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  • $\begingroup$ I read this paper (PDF) last week, and today this question popped up again. Usually I would say that passive repeaters don't work, do the maths. But read the paper - even a small scattered can help a lot if you're deep in the shadow zone. $\endgroup$
    – tomnexus
    Apr 22, 2023 at 6:34

4 Answers 4

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While passive repeaters do exist, I don't think building one for your apartment would be feasible or useful. As you can see in that article, they are usually quite large.

Moreover, a signal of -65 dBm is not excellent, but it's at least good and will work reliably, given no additional problems. So this doesn't really explain your situation.

In many WiFi receivers, the RSSI, from which that signal level is calculated, is actually a measure of the receiver's automatic gain control (AGC) level. The AGC is responsible for adjusting the gain of the RF amplifier such that the input to the demodulator (the part that decodes the WiFi signal) is at an appropriate level. It's like adjusting the volume on your radio so it's not so loud that it hurts your ears, but also so it's loud enough you can clearly hear it.

However, the AGC responds to noise as well as signal. It can't know the difference, and in fact no receiver can. Were it possible to separate noise from signal then noise wouldn't be a problem because it could just be discarded.

So the more likely explanation is that your packet loss is due to noise. Professional WiFi radios provide metrics on things like CRC errors which quantify noise more precisely, and spectrum analyzers can measure noise directly. Some professional-level WiFi radios even have a crude spectrum analyzer built in. But consumer WiFi radios are unlikely to expose these features, so we just have to guess.

Reducing the noise is the first thing you should try. You might find another channel has less noise. Try using the 5 GHz band if you can: it has more channels, and generally less noise.

If you've done all you can to reduce noise and you still have problems, you can increase the signal. If you can't move the AP closer, then you could try a directional antenna. If that won't work, then a WiFi "range extender" is an active repeater that is pretty cheap. Using such a repeater does mean you will be making roughly twice as much noise for your neighbors, but maybe that doesn't bother you.

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This is an old question, but thought I would add my $.02 worth. We used passive repeaters in microwave work to get a signal around a building. It was nothing more than two dishes with a waveguide between them. The antennas were where they needed to be to get around an obstruction.

I would try getting two Wi-Fi antennas, the kind that come with a router, and the proper connectors to hook a short cable between them. Place one on the router side of the wall and the other on the computer side, the closer you can get them to both will help.

They also might work better if they are mounted on some sort to reflector. You could try a piece of aluminum foil about 6 inches in diameter and if you see a better signal use something more substantial, a small pie pan or the bottom of a large coffee can.

As to my real world example, at that time, the microwave power output from the four different transmitters was 100 milliwatts each over a 15 mile path and the passive repeater was 5 miles away. We had another one nearer the source where we needed to make a 120 degree turn. That path was only about 5 miles and the reflector is what was called a 'billboard' since it was huge.

Both ends of that link used periscope antennas, dishes firing up the tower to two billboard reflectors, so there was a lot of bouncing around on that path with never a path fade. It was not fun to get them all in alignment though.

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    $\begingroup$ Building one of these with omnis (even with corner reflectors added) just doesn't work out mathematically. The antenna aperture is so small, and the reradiated signal is so many dB down at the receiver, that it contributes even less than the indirect signal they're already getting. It would be more effective to just cover a piece of plywood with aluminum foil and stand it in the hallway at a 45° angle. $\endgroup$ Apr 21, 2023 at 16:51
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at -65dBm you should not experience that amount of packet loss, however; trusting your measurements are correct, there are a couple of things you might be able to do in order to improve without "building a repeater"

If the computer is in a static location, and the router is in a static location (this is usually true in most installs) then you can improve the signal greatly with some handy antenna work.

For the computer, you should get a WiFi card with an external antenna connector, these are not too expensive.

Once you have an external antenna connector on that card, you can use a directional antenna to point at the router. There are various commercial models, or you can home brew.

But before we go there, a little tip in regards to signals in houses/buildings: It is known, and I have positive experience with this, that circular polarized signals have a better penetration-property then linear (Horizontal or Vertical) polarized signals.

Example: I live in a house built in the 18th-century, with 3-foot thick granite walls. I experienced major problems with WiFi distribution, as the signals simply did not travel through the walls. By switching to circular polarized I managed to get reliable WiFi at 2.4GHz throughout the property !

How did I do this:

1) changed the antenna on the router to a "RHCP clover leaf antenna" (you can search for this, there are commercial types, but there are plenty of plans for self-build as well)

2) changed the antenna on the computers which were in a fixed position to a directional antenna, I choose to built a 5-turn-RHCP-helix.

As I now had Right Hand Circular Polarized (RHCP) throughout the property the signals were good enough to use without any "booster/repeater"

I built all antenna's myself, which was a fun project in itself, but I realize that would not be for everyone.

Actually "building a repeater yourself"... I imagine that this would be a very complex and precise project, which you should only do if you are very familiar with the internal workings of such.

If you cannot get the required signal levels with some handy antenna work, I would suggest that you buy a "WiFi signal booster", they are really not that expensive.

YMMV, HTH.

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Another option that could possibly work. If your wireless modem has the capability of being connected by ethernet cable. Just find a place to put modem where it gets the best signal like near a window and as high as possible. Connect the ethernet cable to modem and compute...

I have a similar thing with my wireless internet stick. I build a metal reflector and cut for it frequency of operation at 2600GHz-4G 14db gain with 25db front to back ratio-great signal.

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