
houstonjln
Hi, If I had a wireless g router with a standard 2db antenna , with a laptop with a wireless g adapter, how far away could I go (in feet) staying in the line of sight of the router?
what about a 7db, 14db & 15db antennas?
Please advise, and a have a merry Christmas
Answer
Imagine a light bulb. It radiates light evenly in all directions. That's an isotropic radiator. Antennas are passive devices. They don't amplify the signal. What they do is concentrate the signal power in a smaller volume. Imagine I put a mirror on one side of the light bulb. Now, one side of the mirror is dark and the other side is twice as light. We can say that the mirror is a 3 dBi antenna. 10^(3/10) = 2 Twice as much light on the lit side.
How far your antenna will reach depends on several factors. These include your input power, the cable loss between the source and your antenna, interference in the channel - meaning radio frequency (RF) noise in the atmosphere between your transmitting and receiving antennas, free space loss - which increases by the square of the distance between the transmit antenna and the receive antenna, signal to noise ratio of your source, receiver sensitivity, receive antenna gain, noise temperature of your receive system, and data rate [1]. 802.11g suffers from interference because it operates in the already crowded 2.4 GHz range. Other devices operating in this range include: microwave ovens, Bluetooth devices, baby monitors and (in the USA) digital cordless telephones [2].
For 802.11g, nominal bit speed is 54 Mb/s, but in low signal or noisy environments the transmission speed is slowed to allow more power per bit. For successful reception, the signal power per bit has to exceed the noise power per bit. By slowing the transmission speed, each bit is transmitted longer - giving more signal power per bit. 802.11g specifies DSSS-OFDM modes with payload data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mb/s as the signal to noise ratio decreases [3]. So, how far your antenna reaches is partly dependent on what data rate you're willing to accept.
Free space loss varies by the square of the range. See equation 5.13 in [1]. Expected range for 802.11g is 38 meters (124') indoors and up to 140 meters (459') outdoors in good RF conditions [4].
A 7 dBi antenna will give 5 dBi more than the standard 2 dBi. The math for the range is sqrt(10^(5/10)) = 1.8. The 7 dBi antenna will give you approximately 1.8 times the range of the 2 dBi.
Likewise for 14 dBi, sqrt(10^(12/10)) = 4. Approximately four times the range.
For 15 dBi, sqrt(10^(13/10)) = 4.5. Approximately four and one-half times the range.
There is a handy Radio Link Budget Calculator available online at [5]. Example numbers for the setup with the wireless router and laptop, use:
Frequency GHz: 2.4
Tx antenna diameter: .06
Tx antenna efficiency: .65 (the default)
Tx power at feed (W): .3
Range (km): .140
Bandwidth: 22000000 (the default)
Rx antenna diameter: .01
Rx antenna efficiency: 0.65 (the default)
Rx system noise temp (degrees K): 440 (the default)
Receiver sensitivity -80 (this is a pretty good wireless card)
You'll get -69 dBm at the receiver - about correct for most wireless cards.
These estimates are consistent with my experience. FWIW, I attached the antenna in [6] to my laptop via a short pigtail. Using this setup, I am able to pick up 802.11b/g access points up to about 1/2 mile away.
Also, you might consider switching to 802.11n. 802.11n uses multi-input, multi-output (MIMO) technology. Basically it shifts phase of several small antennas to digitally "steer" the waveform to improve transmission and receive range [7].
If this doesn't help, e-mail me and I can point you to more info on computing link budgets [8][9].
Imagine a light bulb. It radiates light evenly in all directions. That's an isotropic radiator. Antennas are passive devices. They don't amplify the signal. What they do is concentrate the signal power in a smaller volume. Imagine I put a mirror on one side of the light bulb. Now, one side of the mirror is dark and the other side is twice as light. We can say that the mirror is a 3 dBi antenna. 10^(3/10) = 2 Twice as much light on the lit side.
How far your antenna will reach depends on several factors. These include your input power, the cable loss between the source and your antenna, interference in the channel - meaning radio frequency (RF) noise in the atmosphere between your transmitting and receiving antennas, free space loss - which increases by the square of the distance between the transmit antenna and the receive antenna, signal to noise ratio of your source, receiver sensitivity, receive antenna gain, noise temperature of your receive system, and data rate [1]. 802.11g suffers from interference because it operates in the already crowded 2.4 GHz range. Other devices operating in this range include: microwave ovens, Bluetooth devices, baby monitors and (in the USA) digital cordless telephones [2].
For 802.11g, nominal bit speed is 54 Mb/s, but in low signal or noisy environments the transmission speed is slowed to allow more power per bit. For successful reception, the signal power per bit has to exceed the noise power per bit. By slowing the transmission speed, each bit is transmitted longer - giving more signal power per bit. 802.11g specifies DSSS-OFDM modes with payload data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mb/s as the signal to noise ratio decreases [3]. So, how far your antenna reaches is partly dependent on what data rate you're willing to accept.
Free space loss varies by the square of the range. See equation 5.13 in [1]. Expected range for 802.11g is 38 meters (124') indoors and up to 140 meters (459') outdoors in good RF conditions [4].
A 7 dBi antenna will give 5 dBi more than the standard 2 dBi. The math for the range is sqrt(10^(5/10)) = 1.8. The 7 dBi antenna will give you approximately 1.8 times the range of the 2 dBi.
Likewise for 14 dBi, sqrt(10^(12/10)) = 4. Approximately four times the range.
For 15 dBi, sqrt(10^(13/10)) = 4.5. Approximately four and one-half times the range.
There is a handy Radio Link Budget Calculator available online at [5]. Example numbers for the setup with the wireless router and laptop, use:
Frequency GHz: 2.4
Tx antenna diameter: .06
Tx antenna efficiency: .65 (the default)
Tx power at feed (W): .3
Range (km): .140
Bandwidth: 22000000 (the default)
Rx antenna diameter: .01
Rx antenna efficiency: 0.65 (the default)
Rx system noise temp (degrees K): 440 (the default)
Receiver sensitivity -80 (this is a pretty good wireless card)
You'll get -69 dBm at the receiver - about correct for most wireless cards.
These estimates are consistent with my experience. FWIW, I attached the antenna in [6] to my laptop via a short pigtail. Using this setup, I am able to pick up 802.11b/g access points up to about 1/2 mile away.
Also, you might consider switching to 802.11n. 802.11n uses multi-input, multi-output (MIMO) technology. Basically it shifts phase of several small antennas to digitally "steer" the waveform to improve transmission and receive range [7].
If this doesn't help, e-mail me and I can point you to more info on computing link budgets [8][9].
questions about wireless signal boosters?

buttcolet
i get a wireless signal from someone is my neighbor hood, its a weak signal but it works. if i get a signal booster can that boost the signal from my neighbor?
Answer
Maybe. Maybe not. A problem with using a signal booster is that it also amplifies the noise. So, you may end up with a stronger signal but your signal-to-noise ratio stays the same. In the presence of noise, you'll still get the same throughput you're currently getting with a weak signal.
A better approach is to use a directional antenna. This helps eliminate noise (from portable phones, microwave ovens, baby monitors, other wireless networks, thermal noise, etc.) from your system because these noise sources won't be in the antenna's field. The "Cantenna" is popular with wifi hackers and wardrivers, it gives 12 dBi gain (15.8 times the unamplified signal).
http://www.cantenna.com/
There's lots of room to play with wifi. I built a long range wifi setup with these parts:
http://www.wlanparts.com/product/GD24-15
http://www.wlanparts.com/product/NL2511CDPLUSEXT2
http://www.wlanparts.com/product/MMCXNM24
It has double the gain of the Cantenna but is still small enough to be portable and reasonably inconspicuous. I mounted the antenna on a camera tripod and pointed it out an upstairs window. With this setup, I am able to pick up over 30 WLANs in my neighborhood. These are within a half-mile to a mile range.
When designing your system, be sure to keep your cables short. With some cables, you'll lose 1 dB or more per meter. Compare this with 0.22 dB per meter for higher quality cable such as LMR-400-DB (see specifications in "sources").
If you're short on cash, you can make a homemade cantenna. With a little more "metal bending", you can modify the feed of a discarded parabolic Dish or DirecTV antenna. You can find directions for these projects on the web.
Okay, so I'm a little geeky -- doing one mile wifi. ;) These guys are over the top. They did 125 miles!
http://pasadena.net/shootout05/
Have fun!
Maybe. Maybe not. A problem with using a signal booster is that it also amplifies the noise. So, you may end up with a stronger signal but your signal-to-noise ratio stays the same. In the presence of noise, you'll still get the same throughput you're currently getting with a weak signal.
A better approach is to use a directional antenna. This helps eliminate noise (from portable phones, microwave ovens, baby monitors, other wireless networks, thermal noise, etc.) from your system because these noise sources won't be in the antenna's field. The "Cantenna" is popular with wifi hackers and wardrivers, it gives 12 dBi gain (15.8 times the unamplified signal).
http://www.cantenna.com/
There's lots of room to play with wifi. I built a long range wifi setup with these parts:
http://www.wlanparts.com/product/GD24-15
http://www.wlanparts.com/product/NL2511CDPLUSEXT2
http://www.wlanparts.com/product/MMCXNM24
It has double the gain of the Cantenna but is still small enough to be portable and reasonably inconspicuous. I mounted the antenna on a camera tripod and pointed it out an upstairs window. With this setup, I am able to pick up over 30 WLANs in my neighborhood. These are within a half-mile to a mile range.
When designing your system, be sure to keep your cables short. With some cables, you'll lose 1 dB or more per meter. Compare this with 0.22 dB per meter for higher quality cable such as LMR-400-DB (see specifications in "sources").
If you're short on cash, you can make a homemade cantenna. With a little more "metal bending", you can modify the feed of a discarded parabolic Dish or DirecTV antenna. You can find directions for these projects on the web.
Okay, so I'm a little geeky -- doing one mile wifi. ;) These guys are over the top. They did 125 miles!
http://pasadena.net/shootout05/
Have fun!
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