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Two factors affecting Wi-Fi strength could be the amount of metal construction or the number of electronic devices between the antenna and the computer.

I'm at work on their Linksys Wi-Fi. Some days, the signal reaches down one floor and 20 feet. And some days, it does not. The signal reaches further on the same floor or directly below. Both antennas are pointing straight up. Outside the brick building, the signal reaches much further diagonally (but not inside.) Why does the signal strength change? I tried to track the weather, but couldn't find any pattern. I'm in northeastern Rhode Island. At home, in a standard wooden house and it doesn't change.

In this excerpt from Answercast #54, I look at some possible causes of interference to a Wi-Fi signal at a business location.

Wi-Fi signal strength

So, there's a lot of different things that can affect Wi-Fi signal strength.

Certainly the amount of metal. I'll just say that "generic metal" between you and the antenna can decrease the signal strength. That's why Wi-Fi will probably range more outside than it will inside as you go through multiple walls, multiple levels of construction, and multiple types and amounts of metal.

Interference

The other thing that can change a lot from time-to-time is other interfering equipment. For example, I know that in the home, the Wi-Fi signal may be affected when the microwave is running.

In a business, there are so many different pieces of equipment that could potentially be interfering that it really doesn't surprise me too much. Once you achieve a certain distance between your computer and the antenna, different pieces of equipment in the area (not even necessarily in a straight line, but just in a general area) could potentially be interfering with the signal, if they're turned on or if they're running or if they're doing something specific.

Weather and sunspots

Finally, I'm of the opinion that the weather doesn't necessarily affect Wi-Fi that much - but I believe it's possible that sunspots will!

Sunspots are one of those things that we don't think of very often... they don't really have that much of an effect. But in reality, they can affect various types of radio transmissions, of which Wi-Fi is really nothing more.

Wi-Fi is in fact just another form of radio. Sunspots, depending on their intensity and their timing and all sorts of other things, potentially could factor in to all of this.

If you wanted to do the research, that might be one of the things to do. Find a sun spot tracking site and see if there's a particularly high number of sun spots at the time you see things not working properly.

Building construction and metal

But ultimately, I want to put more emphasis on:

  • The amount of metal construction between the antenna and the computer;

  • And the number of potentially interfering devices, electronic devices, that may or may not be running from one time to the next.

End of Answercast #54. Back to - Audio Segment


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The Ask Leo! Answercast is a production of Ask Leo! and is copyright 2012. Thanks for listening, I'm Leo Notenboom and I'll be back soon with another Ask Leo! Answercast.

Article C5835 - September 20, 2012 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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8 Comments
Ken B
September 20, 2012 7:55 PM

FYI - It's not just metal construction that can interfere with WiFi signals.

If I stand in our kitchen, near the doorway into the office, such that the desk with the router on it (about 10 feet away) is in view, my computer shows "4 bars" of signal strength. If I step 2 feet to the right, where the desk is no longer in view, the signal drops to "2 bars". The difference is the 19th-century solid brick wall (no metal) now blocking the signal.

steven
September 21, 2012 4:30 AM

The work building is mostly a brick building

RJ
September 21, 2012 9:03 AM

Please tell me you are kidding that Wi-Fi signal may be affected when the microwave is running, thats intresting to know

Scott Currier
September 21, 2012 9:42 AM

The signal arriving from the base station to your computer is going to travel over multiple paths. The signal will arrive at your computer and combine in the antenna. The combination of signals arriving from different paths can be destructive or constructive meaning that they can either add to the signal and make it stronger or they can cancel the signal and make it weaker or disappear. At 2.4 gHz just about anything can reflect the signal. People walking, a file cabinet drawer opening, a door opening or closing. If you're using a notebook, a slight change in the location of the notebook can make a big difference. If someone puts something down near the base station, that may account for the change in signal strength, if it's a big enough object. On days when the signal strength is weak, what is different? Go upstairs and have a look. Is anything near the base station that usually isn't?

A vertical antenna on a base station radiates more out than up or down. Reflections from surrounding objects usually will negate that effect somewhat.

Some microwave ovens do operate in the 2.4 gHz range and thus could easily interfere with wifi operating in the same frequency range.

Wifi base stations typically don't operate at very high power. 13 to 15 dbm is typical. That's 20 to 30 miliwatts approximately.

The best solution to a problem like this is to put base stations in all areas where wifi is needed and not rely on signals traveling through floors.

This is especially important when you're dealing with portable handheld devices like phones that have wifi. The antennas in those devices are typically very small and inefficient. The antennas in most notebooks that I have tested have been pretty good.

Another possible solution is to try a wifi repeater placed on the floor below the base station. Not one of my favorite solutions. Some wifi cards don't work well with repeaters. Your capacity going through a repeater is less than half than if you were not going through a repeater. However, that may not be a problem.

I'd like to suggest that since your company owns the base station, you may want to ask them to move it to a different location. Try several and see if you get more reliable performance.

The real solution though is to properly cover the area with additional base stations. Base stations are cheap and easy to setup.

Mark J
September 21, 2012 12:11 PM

@RJ
Microwave ovens, garage door openers, TV remotes, baby monitors etc. operate at the same frequency as WI-FI signals. Some routers allow you to change the channel of your WI-FI signal and in some cases that can improve the range.
Here are a few tips on improving your signal.
Wireless tips from Microsoft

Peter Wall
September 21, 2012 12:28 PM

Wikipedia contains an article discussing "Radio Frequency Interference" which makes for an interesting read on the subject. I'm sure it also has articles discussing the transmission characteristics of various electromagnetic band widths through various substances, including metals and other construction materials for anyone taking the time to search.

Alex Dow
September 21, 2012 12:31 PM

Agreed with Scott Currier's comments.

Additionally, as the microwave radiation used is in the same and similar bands as microwave cookers, just like the meat you put in to that cooker, your body can absorb it and heat up, fortunately very slightly.

The liver and kidneys are particularly affected if you are in the path of a high-power radar system.

Think of a small LED/LCD/flashlight bulb being substituted for the WiFi aerials, both at the router and in your computer.

That is the level of signal that the system operates at.

Apart from the reflections caused by metallic structures, as in radar, water in all its different phases, solid/ice, liquid/water, gas/steam, water vapour etc, also absorbs microwave radiation, the very basis that the mictowave cooker works on.

Even boiling the kettle in your kitchen, producing steam condensing in to water vapour will have an attenuating effect.

High humidity in your workplace could very much reduce the signal strength.

It could even be leaf growth on plants and trees, particularly if moving in the wind.

When you have knowledge of all/most/many of the factors involved, it's a miracle that the system works at all.

This also applies to Mobile/Cell phones etc.

Scott Currier
September 21, 2012 6:08 PM

It's amazing Alex how much reflection and change in signal strength at high UHF when it's windy out. I remember in the analog cellular days sitting upstairs with my Diamondtel 92T transportable phone and watching the field test mode. The signal was going up and down. Every time I looked down at the phone it was on a different setup channel. Reflections would cause one cell to fade and the phone would lock onto another. Being on the top floor and on the side of a hill, I was line of sight to 5 or 6 towers. It was kind of interesting to watch.

With the low price of base stations, in work environments I favor a base station in every room where service is required. Not only do you eliminate the link budget problems of going through multiple walls but you get better performance.

If all clients can hear each other then collisions will be minimized which will increase throughput as well.

The attenuation due to walls and ceilings is an asset, not a liability. It should be used to minimize cell size and maximize capacity and performance.

In my opinion the ideal method is to forget 2.4 gHz and use 5 gHz or if you need the backwards compatibility, use dual band base stations.

If all of the base stations are plugged into the same network hand overs from base station to base station as a client moves around should be seamless and transparent.

One other thing, person asking the question talked about "1 floor plus 20 feet". That sounds to me like being one floor down and instead of being under the base station, you're off to the side.

The signals are attenuated more when passing through the floor at an angle.

The other issue that we don't really have an answer for is whether the signal strength is really decreasing or is the signal disappearing due to interference.

Either way, the way to solve the mystery is to look for what is changing on the days that the signal isn't there. Something is different. What is it?

For capacity purposes I use 3 base stations at home. One upstairs covering 3 users and two downstairs. One at 144 mbps on a 20 mHz 2.4 gHz channel dedicated to a computer I'm using partially as a file server, the other is a 54mbps base station used with clients that support only 802.11g.

Unfortunately there are only 3 non overlapping channels on 2.4 gHz so I'm kinda stuck right now but I have no capacity or signal issues at this time.

At work I use three base stations that provide the two floors of the office a very strong signal everywhere. Important for mobile phones, they have lousy antennas in them due to lack of real-estate. It also looks better if everyone has a nice strong signal where ever they are in our office. Base stations are cheap. No need to skimp.

I just bought two base stations for under 20 bucks each.

I was intrigued because they can be used as base stations, clients, universal repeaters, and WDS.

I have a location where I don't have an ethernet run from the back of the location to the front.

I setup one of these cheap base stations as a standard access point. 150 mbps using a 40 mHz wide channel. I set the other base station up as a client and configured it to connect to the first base station. That turned it into a wireless bridge with 4 ethernet ports. I plugged in the two computers and 1 network printer into it. So far so good.

We'll see how long they last.

I think I'll order a few more to play with in various modes.

Just wish they did 144 mbps in a 20 mHz channel instead of requiring 40 mHz but what do you want for such a low price?


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