How far will my wireless signal go?

March 13, 2009 2:25 PM

How far will a 35dB 2.4GHz (b/g) signal travel indoors with a ceiling mounted dome antenna?

If I get this with this and this, about how far will my resulting signal travel? The calculator I tried is very hard to understand and interpret. Would it work within a 200ft radius in a small coffee shop seting? TIA

posted by jammnrose to computers & internet (5 answers total)

Probably the AP+antenna alone will work for 200 feet. It will vary a lot based on the environment though. My suggestion would be to try the AP+antenna and then add the amplifier if that doesn't reach far enough. But without any obstructions, you would expect a consumer grade AP like that to reach 200 feet by itself (but that's about the limit)
posted by GuyZero at 2:31 PM on March 13, 2009

I agree with guyzero...

(Your spec "35bB" should be relative to something, so I am assuming it's +35dBm or about 3 Watts.) The amp you reference is also not spec'd to deliver more than +30 dBm, which is 1 Watt.

Bumping that signal to 3W will make it go a long, long way... but 802.11 is bi-directional, so you've got to get back to the AP, and your basic MacBook isn't going to radiate 3Watts.

Methinks skip the amp, get a splitter and two antennas. Test and if you need more power, you'll know.
posted by FauxScot at 3:16 PM on March 13, 2009

I assume the OP got 35 dB by adding the 30 dBm amp plus a 5dB antenna, which isn't exactly how it works, but I flunked antennas in fourth year so I won't get too preachy.

The amp is only necessary if the AP and antenna are really far apart and there's a lot of line loss. Because the OP can presumably stick the AP where every he wants this shouldn't happen. Run ethernet to the AP, put the AP near the antenna.

If the AP has two antennas then you could maybe use two external antennas but stock 802.11g has no provision for dealing with multipath issues - most consumer-grade 802.11g units simply use whichever antenna is getting a better signal, only using one at a time. If you got a 802.11n unit it might be able to use multiple antennas simultaneously.
posted by GuyZero at 3:31 PM on March 13, 2009

Hard to say, calculating antenna gain is beyond my current math skills. It might cover the entire area, but I can't imagine you'll have great performance 100 ft away from the wireless antenna.

A cheaper and more scalable solution would be to buy the several linksys wrt54gl's (2 or 3) and chain them together into a large wireless networking using WDS (wireless distribution system). The first one would be connected physically to the cable/dsl internet connection, and the others can be placed anywhere with a power source (within the range of the wireless network).

The idea usually is to set the same SSID on each wireless router, disable the DHCP server on all but one router, and do some trickery with the MAC addresses.

There are several open source firmwares for the WRT54GL that provide different interfaces and make it easier to setup things like WDS. I like the tomato firmware, it's trivial to install, just download the latest firmware, connect to the linksys and open the right tab to restore the firmware image.

Here is how to setup WDS in tomato
posted by zentrification at 3:47 PM on March 13, 2009

802.11 is bi-directional, so you've got to get back to the AP, and your basic MacBook isn't going to radiate 3Watts.
posted by GuyZero at 6:31 PM on March 13

This is the key, and I just wanted to highlight it. You can have all the Tx power in the world on your AP, but a normal laptop a mile away won't be able to connect. However, big antennas work on sending and receiving, so slapping a big antenna on that WRT54GL (nice choice, btw) will work wonders.

As a data point, I have a WRT54GL in the basement of a 2 story house, with two 7dBi antennas attached, plus using DD-WRT firmware boosting Tx power to 84mW from the stock 27mW. The result is that, most of the time, devices get reasonable signal strength on the 2nd floor of the house (diagonally separated, with two floors and a few walls in between). My main PC (also on the 2nd floor) has another 7dBi antenna attached to it, and it gets a very good signal.

Spend some time learning about antennas, and then when you decide on them, spend some time playing with orientations until you get them just right. Assuming the coffee shop is a single floor (or even two), a pretty simple setup should work very well. You may even be fine with an unmodified WRT54GL. Remember, the signal will travel very well through open air. It's mainly walls and other objects will cause reflections and interference that can weaken the signal.
posted by knave at 8:13 PM on March 13, 2009