Laptop + Wireless + Concrete wall.

Oh yeah one more little detail...

Wireless router has to work with skype, since that is used sometimes as well by mammie and certain other people ;) :) like probably family members ;)

Bye, Skybuck.

Skype has nothing to do with it.... Routers come in two flavours- cable or telephone line - get the right one! Get a 'high power' router + high power wireless card for the laptop. Can only tell you about netgear...

should go through a certain amount of concrete,not directly, but via windows, doors, glass etc.

I'm not so sure about that...

If skype uses tcp/ip or udp... and the router does NAT... then I can imagine some sort of problem...

I saw at least one user comment mention that some routers have problems with "voip"... and thus could include skype and I think skype was mentioned too...

Good tip. With cable you mean utp ?

That's what wireless N is for ?

Hmm not much use I'm afraid... it will have to go through concrete directly... at least floor/ceiling, and perhaps also walls if place on floor level.

I might give it a try anyway.

Bye, Skybuck.

skype works 100% with my netgear router...

The big problem isn't just the concrete itself... it's also the rebar.

Almost all concrete installed these days (and for many years) is "reinforced". The concrete is poured around a mesh (usually) of steel bars or wires, which increase the concrete's ability to resist breaking and fracturing.

Between the steel (which is both conductive, and lossy) and the concrete itself (which retains some amount of moisture, and contains salts, and is thus both conductive and lossy) concrete serves as a pretty good absorber of most radio-frequency energy. A well-built concrete building behaves like a crude Faraday cage... RF on the outside doesn't get inside very well, and RF on the inside doesn't leak out efficiently.

Interior walls made of reinforced concrete will have a similar effect.

This isn't an issue just for WiFi. It also affects other radio frequencies to a similar degree (although the attenuation differs). AM radio, FM, UHF and VHF radio, cellphone signals... all are greatly weakened by going through concrete.

Wood and sheet-rock do attenuate WiFi signals, but to a much lesser degree.

On the other hand, wood house-sheathing or interior sheet-rock walls which contains a metallized plastic film as part of a "vapor barrier" or energy-saving system, will act as a extremely efficient barrier to WiFi and other radio signals.

They'll bounce, and they'll also go right through the walls to a significant extent. The wireless system's range, indoors, will be quite a bit less than it would be outdoors in "clear air" but it won't be too bad.

Try sticking the router in the closet... just configure it stand-alone and don't worry about running the UTP cable to the rest of your network. Test the signal while walking around the house, and see where you can and cannot get adequate signal coverage. There's a fair chance it will work acceptably well.

Cellphone systems are affected in the same way WiFi signals are... they don't go through concrete efficiently, either. If you've ever had to wave a cellphone around to get service while indoors, or have had to walk outside to get enough bars to make a call, you'd see this same phenomenon.

Some commercial buildings now contain cell-phone "repeater" systems (wired up to antennas on the roof) or "picocell" or "femtocell" stations (small, low-power miniature "cellphone towers" connected to the Internet), precisely to work around this problem.

e more little detail...

Skybuck specifically said he wanted a router that could go through wood. I know Sears, Black & Decker, Dewalt, and Ryobi make several good ones....

The big problem is the water. The spacing of rebar is sufficiently wide that 2.4GHz will mostly go through quite easily. Some gets reflected, but most will pass. However, water absorption is another story.

Welded steel mesh is usually used for floors, not walls.

Yep. Iron oxide, also known as ferrite, is used in many RF attenuation applications (i.e. ferrite beads). The surface of stealth airplanes, ships, tanks, etc use various iron oxide compounds as an RF absorber to reduce radar reflections. Since RF likes to flow on the surface of conductors, the surface coating of rust on the rebar makes a really nice absorber.

I'm not sure, but I believe concrete is about 1/3 water. Hit some concrete with a cutting torch and watch what happens when the water turns to steam.

Again, it depends on the water content. Wet wood blocks fairly well. Dry wood will pass most RF. Sheet rock or dry wall sometimes comes with aluminium backing, which is great for heat retention, but also doesn't pass any RF. I have a customer with a house full of the stuff. No RF goes between rooms, except through the open door. Using a cell phone inside is a wasted effort (because the windows are also coated with titanium dioxide Low-E for energy efficiency).

Oh-oh. I haven't seen any of that. Most of the vapour barriers I've seen are just plastic or kevlar material. Looks like you're right:

Even if they do bounce, he'll probably have more than one path between the access point and the client radio. This is a good thing for MIMO and a guaranteed flaky signal for 802.11b/g.

Nope. Same problem, but to a lesser degree. The difference is that cellular transmitters are narrow band, while wi-fi is wide band. You can trade range for bandwidth, which is why 1Mbit/sec 802.11 data goes MUCH farther than 54Mbits/sec 802.11g. That's also why the access points slow down the transmission rate when the signals are full or errors. To get 25Mbits/sec thruput with cellular, you'll need WiMax, HSDPA, or other 3GPP modulation scheme, which will have similar issues. Also, cellular is designed to deal with interference issues, while Wi-Fi is a big free for all. If your access point was located on a rooftop or tower, in an area with little interference, you too would have great penetration and range. This is exactly what many WISP (wireless internet service providers) are going with varying levels of success.

I'm making good money selling and installing those.

Energy efficient homes tend to be RF screen rooms.

There are powerline networks to be considered. I installed a Coax system in my house (Netgear MCA1001) which works great. By the way I hook the laptop up through the Coax network to my large LCD TV and use the TV as a monitor. My lowbrow friends come over with their beer and always want to browse You Tube (most of them are in their sixties and should know better :-)). Though I guess free beer is free beer. I control the laptop with a wireless keyboard and mouse.

Skybuck Fly> Hello,

The Subject line says concrete, but I suspect that there are those that have trouble recognizing the difference.

That's just step one. Please suggest that he install a passive repeater on both sides of the hole. That's where you mount an antenna on each side of the wall, with a coax cable in between. It's suppose to pass RF through the wall via the coax. Something like this:

The reason I want you to suggest it is so I have an excuse to calculate and explain (again) why it's generally a lousy idea.

actually i read it as BOTH (wood AND concrete, sounds like wood on concrete....)

He wanted to go through his head? How about a .357?

Should we tell Skybuck to put a fan on the LAN cable so it doesn't overheat?

No. I don't think Mr Starbuck has any fans or supporters.

I still like the passive repeater through the wall idea. That's not because it won't work, but because the similarity between the old two tin cans and a string is so cool. With two coffee cantennas and some coax, it's much the same, except it's for wi-fi.

I suppose it would be useful to remind Mr Skybuck that buying a computah for a friend or relative also enlists Mr Skybuck as tech support and rescue service for the life of the product. It's the last of the truly unlimited warranties. Never sell a used car or computah to a friend is good advice.

snip

Jeff, I'd like to hear more about why this is a lousy idea. (sorry I seem to have missed when you explained previously). My News supplier (Newsguy) has pretty good retention, so a clue as to when it was posted should work.

-- Charlie Hoffpauir

Everything is what it is because it got that way....D'Arcy Thompson

Methinks it's easier to just recreate the calculations, rather than doing battle with Google Groups search. I posted some calcs to alt.internet.wireless about 2 years ago.

Let's start with straight line radio path. 30ft long. 2.4GHz At one end, a typical +17dBm xmit access point, with a 2dBi gain omni antenna. At the other, a typical laptop, with a 0dB gain internal PIFA antenna. 0dB coax cable losses.

Plugging into a handy calculator at:

Remember to divide the 30ft by 5280 ft/mile. I get -40.3dBm signal level at the laptop receiver.

Next, lets cut the path in half by erecting an RF impervious wall at the 15ft point. Through this wall, is a small hole necessary to pass some coax cable. On each side is a fairly typical 12dBi gain panel antenna. This thing is called a passive repeater.

Starting with the same +17dBm access point, into a 2dBi omni, but with only 15ft of path length, into a 12dBi panel antenna, I get a -22.3dBm signal level at the coax cable going through the wall.

This -22.3dBm signal becomes the transmit signal for the other side. It goes to a 12dBi gain panel antenna, 15 ft path, and to a 0dBi antenna in the laptop. That results in a -63.6dBm signal level at the laptop receiver.

Comparing the staight line path with the passive repeater system, I get a net loss of: -40.3dBm - -63.6dBm = 23.3dB difference That's quite a bit of extra loss.

So, what happened? The omni antenna on the access point sprays RF all over the place. A small part of this RF hits the 12dBi gain panel antenna, which accounts for most of the difference.

I made an attempt to use somewhat realistic numbers for this example.

15ft would be about the length of a typical room. 30ft would be two adjacent rooms. With the passive repeater -64dBm receive level is actually a fairly respectable and usable signal. Using these examples, and assuming there are no reflections, a passive repeater should work. However, with a longer path, disconnected rooms, added cable loss, and lower gain antennas, the numbers get worse rather quickly.

I had to play "tron evolution" so it was postponed until today ;) :)

It's now morning and maybe we go take a looksy today ;)

It's a good thing too.. because now I am pretty sure that intel core i5 is probably better choice than amd phenom II... because intel core i5 has sse

4.1 and sse 4.2 which has some interesting new instructions as well.

Though perhaps the website I saw was a lie... perhaps intel core i5 only supports 4.1 ???

Hmm...

Bye, Skybuck.

What does the warden have to say about your drilling holes in the walls of your cell?

Zullen we hier weer eens Nederlands als voertaal gaan gebruiken? Tenslotte is het een NL-groep!!!!

Not much. After prisons are done installing cell phone jammers, the next step will possibly be Wi-Fi and Bluetooth jammers.

Of course, every time you mention cell phones, someone always complains that the radiation is affecting them:

How about 210 watts on 5 bands for $9,000?

Be the first on your (cell) block to dominate the world.