Wireless Range

[theprez98]

When searching for a wireless card, people often want to find one with the best range. Most often, this decision is solely limited to the transmit power of the card. While transmit power is one factor in determining range, there are others that ought to be considered when determining overall range.

As 802.11b/g uses 2.4 ghz, which operates like any other radio frequency signal, we can use the basics of RF signal propagation to determine range. There are five basic components which effect signal propagation:

*Transmit power
*Transmit antenna gain
*Frequency and distance (path loss)
*Receiving antenna gain
*Receiver sensitivity

There are other factors which effect signal loss as well: cable losses, RF opaque materials in the signal path, etc.

Because wireless communication is a two way process, we may also have to include the same five factors in reverse. While 'transmit power' referred to your wireless card, on the return trip 'transmit power' refers to the access point. Likewise, 'receiver sensitivity would refer to your card as opposed to the access point, and so on.

The point of this post is to demonstrate that your 250mw or 300mw or 600mw card may have significant power out, but that is only one of the factors that determine range.

This is meant to be a very basic primer in wireless ranging. There are very detailed range equations out there. If you're interested, Google "Friis transmission equation" and go from there.

[Guanji]

nicely put.. nothing else to add to that.

[streaker69]

nicely put.. nothing else to add to that.

Then why did you feel the need to add absolutely nothing to the thread? Trying to get your post count up?

[theprez98]

Then why did you feel the need to add absolutely nothing to the thread? Trying to get your post count up?
Apparently!

[-=Xploitz=-]

I just wanted to use this thread to vent on my latest purchase....

I spent $80 USD on a device called a "WiFi Signal Booster" made by Hawking Technology. IMO..this thing is a complete piece of shit and a waste of money. Heres the link to the product for more info...So Called Signal Booster (http://www.hawkingtech.com/products/productlist.php?CatID=32&FamID=72&ProdID=187)

And heres a pic PIC HERE (http://www.microcenter.com/image.phtml?id=0213362&sku=450775)

Man..I pluiged this in..hooked it up to my modded card..used my 10dbi omni.....
set the power to 100mw..no change
set the power to 200mw..still no change..
set the power to max..500mw!!..still no noticeable change. :mad:
What a freaking waste of money!:mad: Good thing Microcenter told me I had 30 days to try it out and if I didn't like it I could bring it back!

They told me this would extend the distance on my card and I'd see "dramatic" changes. What a crock of B.S!! I even disconnected my 10dbi omni and used their 2 dbi omni..still nothing. I know I had everything hooked up right, cause even with the power cord to it unplugged...I could move my antenna that is still connected to it closer to my AP..and the power levels rose...so..IMO..don't buy this. I'm considering buying an alfa 500mw:confused:...but I hear the driver is buggy...I need to "search" here and air crack for more details on the Alfa 500mw. Cause from my understanding..there are 2 different models..and 1 of them doesn't work right with BT2...so off I go now to search land.

[harry]

Environmental conditions have a serious affect on propagation too.

During the early morning or very late at night propagation is at its best and attenuation is at it's lowest; damp and humid conditions help the signal propagate even further.

If you get intermittent connectivity with an AP during the day, try again at night or in the morning and chances are you will get a workable signal. If the air is damp or the ground is wet maybe due to rain or dew then your further your chances even more of getting a workable signal . Attenuation can be reduced by up to 45% on a damp cold morning/night.

If it is a dry hot day and you are in a busy area then anything up to +60% attenuation is possible.

(Although this does still apply somewhat if the AP is in your own house, it obviously applies more if the AP you are trying to associate with is in another building or similar)

Just because you can receive a signal from an AP does not mean you can send to it, as APs usually have a lot more range than a wireless adaptor.

[-=Xploitz=-]

Well, I did this last night..so theres a plus. It rained that day..so another plus. The AP is in my house..15 feet away..so another big plus. So I met all the "optimal" environmental factors according to you harry..so maybe I have just "peeked" my cards possible performance levels already??lol:D

[PrairieFire]

You might have a bad unit but I would try it with another card that has external antenna connectors before ruling it out as junk. The FCC data (https://gullfoss2.fcc.gov/oetcf/eas/reports/ViewExhibitReport.cfm?mode=Exhibits&RequestTimeout=500&calledFromFrame=N&application_id=509349&fcc_id=%27SOYHSB2AP%27) shows decent gain. I paid 200+usd for a 1 watt bi-directional amp and have had good results with it.

[-=Xploitz=-]

You might have a bad unit but I would try it with another card that has external antenna connectors before ruling it out as junk. The FCC data (https://gullfoss2.fcc.gov/oetcf/eas/reports/ViewExhibitReport.cfm?mode=Exhibits&RequestTimeout=500&calledFromFrame=N&application_id=509349&fcc_id=%27SOYHSB2AP%27) shows decent gain. I paid 200+usd for a 1 watt bi-directional amp and have had good results with it.

Hmm...unfortunately its my only externally connectible card I have ATM...but ill play around with it. I only messed with it for 5 minutes. Thanks for all your suggestions PrairieFire and harry. :)

[-=Xploitz=-]

Ok..just a quick followup that will make me look like a complete moron..but oh well...I post the truth no mater if I look bad or not.

I take back my previous complaint about the $80 USD hawking wifi signal booster. Problem was..I was 2 close to my AP to notice any difference. While "war-sitting"..lol in my house, there is an AP that has always shown up as a 2 - 4 power level on my airodump screen. So...I opened a new airodump screen with just my 10dbi omni connected..and the APs power level is at 5. So I plug in my amp and connect my antenna to it..and lo and behold..Im reporting a constant 15-19 power level. The signal quality was a sketchy 50-85..and unstable...but now its constantly 100..seldomly dropping at all to the 90's. So it appears that it works and I am a moron. But keep in mind that I was doing this to get better signal in my house from only 1 room away..and not to "wardrive" for other peoples AP's. Whats the moral of this story?? Test it all out beforehand or else you could be taking back something that worked extremely well to begin with. This has been a learning experience for me. I just never really look for other peoples AP's because I'm not trying to hack em. Nice to know though that a product like this works so well that it could be very easily used for mischief in the wrong hands though. I mean someone could easily break into my WEP protected router from over 1000 feet away with this AMP and antenna setup I got. Now I just need to "shield" my AP from all sides except for line of sight just to add an extra measure of security, and put WPA2 TKIP+AES back on my router!! But then again..I am a very paranoid individual when it comes to hackers.

[Barry]

Not trying to add more to a "sticky", maybe theprez could move some of the off topic content, but if you search over at the netstumbler forums, I think there's a thread on wifi killing paint. Might be time to repaint the house.:p

[streaker69]

Ok..just a quick followup that will make me look like a complete moron..but oh well...I post the truth no mater if I look bad or not.

I take back my previous complaint about the $80 USD hawking wifi signal booster. Problem was..I was 2 close to my AP to notice any difference. While "war-sitting"..lol in my house, there is an AP that has always shown up as a 2 - 4 power level on my airodump screen. So...I opened a new airodump screen with just my 10dbi omni connected..and the APs power level is at 5. So I plug in my amp and connect my antenna to it..and lo and behold..Im reporting a constant 15-19 power level. The signal quality was a sketchy 50-85..and unstable...but now its constantly 100..seldomly dropping at all to the 90's. So it appears that it works and I am a moron. But keep in mind that I was doing this to get better signal in my house from only 1 room away..and not to "wardrive" for other peoples AP's. Whats the moral of this story?? Test it all out beforehand or else you could be taking back something that worked extremely well to begin with. This has been a learning experience for me. I just never really look for other peoples AP's because I'm not trying to hack em. Nice to know though that a product like this works so well that it could be very easily used for mischief in the wrong hands though. I mean someone could easily break into my WEP protected router from over 1000 feet away with this AMP and antenna setup I got. Now I just need to "shield" my AP from all sides except for line of site just to add an extra measure of security, and put WPA2 TKIP+AES back on my router!! But then again..I am a very paranoid individual when it comes to hackers.

So you learnt a lesson, that's good, here's another one.

Instead of trying to improve conditions on the client side, it would have been more wise to improve conditions from the AP side. To get adequate coverage in my house, I have 4 AP's scattered throughout. One in the detached garage, I have an WRE54G in the backroom that links to a WAP54G that's in the pantry, and then there's a WAP54G that bridges into the same WAP54G in the pantry.

I have excellent coverage through out the entire house no matter where I go. When I get done wardriving for the day, I pull buggy into the garage and upload my data right from there instead of hauling the PC inside.

[-=Xploitz=-]

So you learnt a lesson, that's good, here's another one.

Instead of trying to improve conditions on the client side, it would have been more wise to improve conditions from the AP side.


I agree, but the device had only dual SMA connections and my AP has 2 RP-TNC antenna connectors, and I didn't have any converters to connect them to each other.

[Barry]

I agree, but the device had only dual SMA connections and my AP has 2 RP-TNC antenna connectors, and I didn't have any converters to connect them to each other.

Weird, usually Hawking comes with rp-tnc to r-sma adapters. Maybe it's just their antennas. Comp-usa should carry them.

[-=Xploitz=-]

Weird, usually Hawking comes with rp-tnc to r-sma adapters. Maybe it's just their antennas. Comp-usa should carry them.

This one didn't, but its cool. I'm happy with it just as it is. I might go to Fry's electronics and pick up a coupler and play with it and my AP.

[streaker69]

This one didn't, but its cool. I'm happy with it just as it is. I might go to Fry's electronics and pick up a coupler and play with it and my AP.

Don't forget, you can take a whole bunch of 1W amps and plug them in in series to get some really killer wattage, as per Decadude.

[theprez98]

Don't forget, you can take a whole bunch of 1W amps and plug them in in series to get some really killer wattage, as per Decadude.
The moderators and admins of this forum take no responsibility for users' failure to have children if you follow Decadude's instructions!

[-=Xploitz=-]

The moderators and admins of this forum take no responsibility for users' failure to have children if you follow Decadude's instructions!


:D So it will just overload and burn out all of your amps in the series, and fry your nuts at the same time...Kool!! Who needs to pay for a vasectomy when you got free Wi-Fi radiation?:D

[operatorone]

I have gotten my hands on one of these...

http://www.pheenet.com/product/product_info.php?id=100&category_id=32&parent_id=13

but I haven't had a chance to try it yet. I will let you know if I ever get around to it. Is this the same thing you are talking about Xploitz?

[Barry]

:D So it will just overload and burn out all of your amps in the series, and fry your nuts at the same time...Kool!! Who needs to pay for a vasectomy when you got free Wi-Fi radiation?:D

Kinda like my coconut in the microwave experiment? I was really let down by that one. Microwave jumped a bit, but I was hoping the door would come off.

[-=Xploitz=-]

I have gotten my hands on one of these...

http://www.pheenet.com/product/product_info.php?id=100&category_id=32&parent_id=13

but I haven't had a chance to try it yet. I will let you know if I ever get around to it. Is this the same thing you are talking about Xploitz?

Nearly identical. Yes its the same type of amp.

[EnculeurDePoules]

Environmental conditions have a serious affect on propagation too.

During the early morning or very late at night propagation is at its best and attenuation is at it's lowest; damp and humid conditions help the signal propagate even further.

If you get intermittent connectivity with an AP during the day, try again at night or in the morning and chances are you will get a workable signal. If the air is damp or the ground is wet maybe due to rain or dew then your further your chances even more of getting a workable signal . Attenuation can be reduced by up to 45% on a damp cold morning/night.

If it is a dry hot day and you are in a busy area then anything up to +60% attenuation is possible.

(Although this does still apply somewhat if the AP is in your own house, it obviously applies more if the AP you are trying to associate with is in another building or similar)

Just because you can receive a signal from an AP does not mean you can send to it, as APs usually have a lot more range than a wireless adaptor.

I was going to comment on that!!!
It sounds silly but after a year of using wireless, I observed many often changes in the recption while still not moving from my room!
When its rainy its less signals than in other times... sometimes I receive plenty of signals, sometimes not!
Sometimes by moving like 1 meter away I have better signals and so on!!
weird, i'd like to have a tool to mesure exatcly theses!!

[EnculeurDePoules]

and what about the Cantenna?

Apparently I read that normal wireless card in laptops are approx 1-2 db reception, but we can increase up to 10-20 db with a simple home made cantenna!!
Well "simple", I tried to make one I screwed up, but apparently its simple!

example of cantenna:try google, haha!
im not allowed to post urls!

[tybalt]

Didn't see anyone else mention anything about this. But, some of your results might be effected to the use of the 10dBi antenna. When choosing an antenna you have to consider its beam width. Omni antennas once they reach a certain dBi have a very narrow beam width. Typically around 8-10 degree vertical. As compared to my D-Link 7dBi omni which has a stated beam width of 40 degrees. This is what is noted on the packaging. Though manufactures web site if I'm recalling correctly states it have a 27 degree. Either way I too have a 10dBi omni that I had received. The results with the 10dBi are pretty horrible. You really have to tweak it in to find that sweet spot. Even so having a greater beam width can have an impressive result.

In my results living in a rural area. I've been able to detect/authenticate with AP's around ~600ft using the 7dBi. While the 10dBi only picked up a fraction of those APs with a dramatical decrease in S/N ratio. Even using the ever so popular "cheap parabolic reflector" with the 10dBi I still have poor results. While the 7dBi omni and reflector allow me to have a steady consistent 11Mb connection at 500ft. The 10dBi omni and reflector barely allowed a 2Mb connection.

[SLK001]

Since a wifi system is a duplex system, adding power to your end alone makes absolutely no sense at all. You could be 200 miles away from your desired AP and be transmitting 1 MEGAWATT, but without a significant improvement in the receiver sensitivity on your end, you cannot connect (they can "hear" you, but you cannot "hear" them).

If you desire an increase in range, you need to have better antennas (most antennas have the property of reciprocity - the transmit gain is the same as the receive gain). What tybalt said about antennas is somewhat true. Sometimes a 7dBi antenna can appear to perform better than a 10dBi antenna, especially if the extra effort to "steer" the beam is not performed. A co-linear antenna's vertical beamwidth does get smaller as the number of elements increase. That is the price for increased gain in the azimuth. A co-linear antenna is omnidirectional. Above a certain gain requirement, the antenna needs to be directional. But using a directional antenna, you can get some amazing gains (but you have to properly "aim" the antenna). Simple horn antennas can give you gains of 50 or 60. With dishes, the gains can even exceed 200. But, with the increased gain, the precision of the alignment also increases.

So, if you really want to increase your range by adding amplifiers, you need to add the same amplifier to the access point that you added to your station. If not, you have wasted your time and money.

[bobbolo]

When searching for a wireless card, people often want to find one with the best range. Most often, this decision is solely limited to the transmit power of the card. While transmit power is one factor in determining range, there are others that ought to be considered when determining overall range.

*Transmit power
*Transmit antenna gain
*Frequency and distance (path loss)
*Receiving antenna gain
*Receiver sensitivity



Sorry guys if the question is stupid...
but how can i know the receiver sensitivity of the card? i only know that the
transmit power id 300mW, and u correctly told me that transmit power is not all. There is a way to test and judge the others important values of the card? i have a wifi ubiquity pcmcia 300mW.

Thanks in advance,
bobbolo.

[sergeikolomov]

(most antennas have the property of reciprocity - the transmit gain is the same as the receive gain).
"most antennas"... So which antennas don't have reciprocity?

On this topic, external receiver amplifiers used to make sense. But with modern hardware, aren't they obsolete? For example the AWUS036H sensitivity is already at -92dBm @ 1Mbps according to the manual. The Engenius 362EXT is at -96dBm @ 1Mbps, which is pretty close to the thermal noise floor.

[SLK001]

"most antennas"... So which antennas don't have reciprocity? Well, all antennas do. However, antennas with integrated amps do not and I wanted to avoid agruments like "my antenna works well in receive, but like crap in transmit".


For example the AWUS036H sensitivity is already at -92dBm @ 1Mbps according to the manual. The Engenius 362EXT is at -96dBm @ 1Mbps, which is pretty close to the thermal noise floor. Not really. They are "cheating" with their specs. If you look at their spec for a 54Mbps channel, it is -76dBm - not bad, but definitely not state of the art. This is the only measurement that uses the entire 20MHz bandwidth, so this is where your kTB calculation will give you a true representation of their sensitivity. As their bitrate drops, the needed bandwidth also drops, so B has to be adjusted downward. At 1Mbps, I'll be generous and give them a 1MHz bandwidth in which to transmit. This gives them a noise floor of -114dBm. Far from state of the art.

[sergeikolomov]

how can i know the receiver sensitivity of the card? i only know that the
transmit power id 300mW, and u correctly told me that transmit power is not all. There is a way to test and judge the others important values of the card? i have a wifi ubiquity pcmcia 300mW.
You can't determine the sensitivity without equipment which none of us can afford. You have to rely on the manufacturer to tell you the truth. But you can determine the relative sensitivity compared to other cards by just swapping them out and checking which can detect distant WAPs which the other card can't, assuming they have the same type of external connector so you're not changing anything besides the card itself.

[sergeikolomov]

Well, all antennas do. However, antennas with integrated amps do not
Thank you. So it turns out that a nonreciprocal "antenna" isn't just an antenna. That's something I've been wondering about for a while since I've seen references to nonreciprocal antennas sometimes (not worded that way, I don't remember how it was worded, but the point was the same) and I wondered "how is that possible?"

Not really. They are "cheating" with their specs. If you look at their spec for a 54Mbps channel, it is -76dBm - not bad, but definitely not state of the art. This is the only measurement that uses the entire 20MHz bandwidth, so this is where your kTB calculation will give you a true representation of their sensitivity. As their bitrate drops, the needed bandwidth also drops, so B has to be adjusted downward. At 1Mbps, I'll be generous and give them a 1MHz bandwidth in which to transmit. This gives them a noise floor of -114dBm. Far from state of the art.
Yes, I was mistaken about the noise floor. Thanks for the correction.
They're not being misleading with their specs, since they always give the bitrate when they give a sensitivity (they're not like some webcam vendors who say "Up to <some really high resolution>! Up to 30fps!" but don't tell you that the webcam can't do both at the same time). Giving specs for lower bitrates is legitimate, since the WiFi standard allows radios to make the tradeoff when necessary. I was accidentally being misleading when I said -96dBm @ 1Mbps is close to the noise floor (my mistake, not theirs).
But isn't the 362 state of the art if cost is accounted for? Or is there any device for sale which can do better and doesn't cost thousands of dollars?

[SLK001]

Giving specs for lower bitrates is legitimate, since the WiFi standard allows radios to make the tradeoff when necessary. I was accidentally being misleading when I said -96dBm @ 1Mbps is close to the noise floor (my mistake, not theirs).
But isn't the 362 state of the art if cost is accounted for? Or is there any device for sale which can do better and doesn't cost thousands of dollars?When specs are given, the measurement criteria should also be given. What are the conditions that constitute their "sensitivity"? Is it a bit-error-rate (BER) of 5%, or a much more liberal 8, 9 or even 10% BER? That is the problem when comparing specs from different vendors when the conditions aren't properly spelled out.

Given the two models that you stated, the 362 definitely has much better sensitivity that the other model, provided that the test conditions were equal. They both represent pretty much the industry norm. A more sensitive board for this market would not make sense, given the intended use (normal in-home use) and would only meet a specific niche in the market, since the top three design criteria in this market is cost, cost and then cost.

[geedub]

i just picked up the wireless signal booster that xploitz was talking about. it works great, however, you can't use injection with it, at least with the hardware I have. everytime i connected it to the card and started injection, it just starts going really slow almost to a halt, like 3 packets a second. this is with the hawking external usb device, which works great.

[-=Xploitz=-]

i just picked up the wireless signal booster that xploitz was talking about. it works great, however, you can't use injection with it, at least with the hardware I have. everytime i connected it to the card and started injection, it just starts going really slow almost to a halt, like 3 packets a second. this is with the hawking external usb device, which works great.

Sorry to hear that. Perhaps your 2 close? Adding 500mW to your USB is good, but if your 2 close you'll likely produce malformed packets or at the very least "signal flooding" and interference. Try backing off a few yards. ;)

I have no problems at all injecting or catching my handshake with it. I use it with my alfa 500mW making it a 1 Watter!! :cool:

[geedub]

it seemed as if it just got "out of sync" or something, I tried moving further from the AP. It could also be the hawking usb device that i have. either way i went and got my 71 dollars back today.

[Dr_GrEeN]

I got my 500mW amp and Directional antenna today from ebay :D Was $180 but makes a f-n difference or what :D Using net stumbler I can see gains of 20dBm without playing with the direction of the antenna.

But after doing my calculations, I realized that I was over double the law :D In the UK the limit is 20bB. My Netgear WG511T Card is @ 18dBm, the amp is running 26.99dBm give or take because I've modded he power to run from USB and it should be running on a 6v power supply. The antenna is at 12dBi, This give me 39.51dB of power :p well over the limit :D I wondered why they didn't sell em in the UK lol .

[.lonewolf]

I can see why you're smiling :D

How far does your directional antenna reach with your new setup or is it still too early to say? :)

[Dr_GrEeN]

It's to early to say lonewolf, I've only just got it out of the pack. Done a quick job on the USB hack to test to. I'm off to my local electronics shop in a bit to grab a couple of connectors for ease switching between usb and mains power.

This is for my bluetooth packet sniffer to, but by the looks of it my bluetooth mod was unsuccessful :( Oh well back to the drawing board.

For anybody interested heres the pack I got from ebay. The guy is first class as the order came from hong kong and only took 5 days to the uk.

http://cgi.ebay.co.uk/3in1-12dBi-WiFi-Antenna-6ft-RF-Cable-Amp-Booster-500mW_W0QQitemZ270121263736QQihZ017QQcategoryZ6181 6QQrdZ1QQssPageNameZWD1VQQcmdZViewItemQQ_trksidZp1 638Q2em118Q2el1247

[anathema]

Any update on this nice looking setup Dr Green?

Just ordered the Danets Antenna to go with my Alfa 500Mw

[SlingShot]

It's to early to say lonewolf, I've only just got it out of the pack. Done a quick job on the USB hack to test to. I'm off to my local electronics shop in a bit to grab a couple of connectors for ease switching between usb and mains power.

This is for my bluetooth packet sniffer to, but by the looks of it my bluetooth mod was unsuccessful :( Oh well back to the drawing board.

For anybody interested heres the pack I got from ebay. The guy is first class as the order came from hong kong and only took 5 days to the uk.


Wow, what an awesome looking package. Very tempting indeed.. I have an Alfa on order so this would turn that into a monster.. lol.

Regarding the USB mod, was this easy to do? I'm not massively electronically skilled so that could be show stopper if it's tricky to achieve.

[SLK001]

Okay, one last time.

Extra power on a single end is a waste of money (not to mention that it violates the law in many countries). Since 802.11 is a duplex system, both ends of the chain must have the extra power. As an analogy, say that you have two people 1000 yards (meters) apart that are trying to communicate with each other by shouting. This is very difficult at best, but with optimum conditions (very low signal-to-noise ratios), it might be accomplished at a low data rate. Now imagine that one of the parties decides that he is going to "amplifiy" his outgoing signal so that he can now be "heard", so he buys himself an electronic megaphone. Well, mission accomplished! His "signal" is now received loud and clear by the other party. But there is a problem. The other party's signal still is very weak, so the data rate doesn't change.

This means that you have to simultaneously (on a single end) increase both your received power and your transmitted power to have any increase in range. Back to my analogy, had the first person decided to use a large funnel type of megaphone (totally passive, thus bi-directional), he could shout in the funnel when he needed to talk and put his ear to the funnel when he wanted to listen - thus successful two way communications.

The only way to do this for 802.11, is to use an antenna with high gain, which means using a directional antenna - either some sort of dish, or a collinear.

So, if you really want to improve your range, spend all your money on a decent antenna.

[anathema]

Okay, one last time.

Extra power on a single end is a waste of money (not to mention that it violates the law in many countries). Since 802.11 is a duplex system, both ends of the chain must have the extra power. As an analogy, say that you have two people 1000 yards (meters) apart that are trying to communicate with each other by shouting. This is very difficult at best, but with optimum conditions (very low signal-to-noise ratios), it might be accomplished at a low data rate. Now imagine that one of the parties decides that he is going to "amplifiy" his outgoing signal so that he can now be "heard", so he buys himself an electronic megaphone. Well, mission accomplished! His "signal" is now received loud and clear by the other party. But there is a problem. The other party's signal still is very weak, so the data rate doesn't change.

This means that you have to simultaneously (on a single end) increase both your received power and your transmitted power to have any increase in range. Back to my analogy, had the first person decided to use a large funnel type of megaphone (totally passive, thus bi-directional), he could shout in the funnel when he needed to talk and put his ear to the funnel when he wanted to listen - thus successful two way communications.

The only way to do this for 802.11, is to use an antenna with high gain, which means using a directional antenna - either some sort of dish, or a collinear.

So, if you really want to improve your range, spend all your money on a decent antenna.

Regarding this I've seen amps that claim to not only boost the output but also the receive.
I was thinking of getting an amp for my card (not my AP)
Is this possible as the signal being sent by the AP is still the same,

So I can shout louder but if I have a higher receive then I also have a top range hearing aid?.

Sorry to put it into lay-mans terms, but I hope oyu get the idea.

[streaker69]

Regarding this I've seen amps that claim to not only boost the output but also the receive.
I was thinking of getting an amp for my card (not my AP)
Is this possible as the signal being sent by the AP is still the same,

So I can shout louder but if I have a higher receive then I also have a top range hearing aid?.

Sorry to put it into lay-mans terms, but I hope oyu get the idea.

Anything that is going to boost your 'receive' is also going to boost the noise as well.

[hhmatt81]

Anything that is going to boost your 'receive' is also going to boost the noise as well.

Isn't there something to filter the noise?

[Barry]

Isn't there something to filter the noise?

I've not seen anything, though I've never had to look. A properly set up network shouldn't need amplification above spec. Anything you do that throws it out of spec can induce noise.

[radioraiders]

So, if you really want to improve your range, spend all your money on a decent antenna.
...or a receiver with lower noise floor.

[balding_parrot]

...or a receiver with lower noise floor.the antenna route is going to be far more practical and cost effective in a consumer situation like this.

Amplifiers of this type tend to be just cheap wideband amplifiers that amplify everything with very little or in some cases no filtering at all. You would need to be getting into fairly high grade commercial equipment before you would even start to see any kind of reasonably effective filtering involved. None of the above even takes into account the affects cross channel interference or having more than one piece of equipment operating on the same channel will have. That is not saying that amplifiers cannot improve things, just that they are not always the solution they are portrayed as being as they can introduce their own set of problems, and in some cases make things worse.

EDIT:
Nearly forgot to add this important point
ALL amplifiers produce noise, with or without any input to them, just as does ANY electronic circuit.

[SlingShot]

Okay, one last time.

Extra power on a single end is a waste of money (not to mention that it violates the law in many countries). Since 802.11 is a duplex system, both ends of the chain must have the extra power. As an analogy, say that you have two people 1000 yards (meters) apart that are trying to communicate with each other by shouting. This is very difficult at best, but with optimum conditions (very low signal-to-noise ratios), it might be accomplished at a low data rate. Now imagine that one of the parties decides that he is going to "amplifiy" his outgoing signal so that he can now be "heard", so he buys himself an electronic megaphone. Well, mission accomplished! His "signal" is now received loud and clear by the other party. But there is a problem. The other party's signal still is very weak, so the data rate doesn't change.

This means that you have to simultaneously (on a single end) increase both your received power and your transmitted power to have any increase in range. Back to my analogy, had the first person decided to use a large funnel type of megaphone (totally passive, thus bi-directional), he could shout in the funnel when he needed to talk and put his ear to the funnel when he wanted to listen - thus successful two way communications.

The only way to do this for 802.11, is to use an antenna with high gain, which means using a directional antenna - either some sort of dish, or a collinear.

So, if you really want to improve your range, spend all your money on a decent antenna.

Gotta say, that is a fantastic explanation of wireless range - excellent analogy. I must admit it was doing my head in a little trying to think in terms of both the transmission power and the receive etc. The funnel idea does make a lot of sense as you are improving your output but also allowing yourself to 'hear' further.

I'm now looking for a suitable antenna for my new Alfa. It's definetely improved things in my initial tests and it's also nice to see accurate 'pwr' ratings in airodump (my Edimax was totally wrong, showing 100 - or more for all AP's).

Are the Cantenna type devices worth looking into? I'm interested in knowing what kind of practical range can be achieved with a directional antenna. Be quite a cool experiment as I have a lot of open space near my apartment.

[Dr_GrEeN]

I don't know much about these amps but they do make a difference on transmitting and receiving I have found, they are bi-directional amps. Even though the transmit signal may go a lot further than you could receive :D


Low noise RX amplifier is used to pick up weak signal at optimal Signal-to-Noise Ratio (SNR).




Max Transmit Linear Output Power:

500mW/ 27dBm 802.11g

Transmit Gain:

up to 10dB

Transmit Input Power:

0 +/- 2dBm Min; +20dBm Max

Receive Gain:

12~16dB, 15dB typical

Max Receive Input Power:

-10dBm


I thought the amp from ebay took cross channel interference and equipment on the same channel in to consideration and uses tdd to remedy this and improve stability ??? But like I say I know nothing about this :D

[radioraiders]

the antenna route is going to be far more practical and cost effective in a consumer situation like this.

Amplifiers of this type tend to be just cheap wideband amplifiers that amplify everything with very little or in some cases no filtering at all. You would need to be getting into fairly high grade commercial equipment before you would even start to see any kind of reasonably effective filtering involved. None of the above even takes into account the affects cross channel interference or having more than one piece of equipment operating on the same channel will have. That is not saying that amplifiers cannot improve things, just that they are not always the solution they are portrayed as being as they can introduce their own set of problems, and in some cases make things worse.

EDIT:
Nearly forgot to add this important point
ALL amplifiers produce noise, with or without any input to them, just as does ANY electronic circuit.
Receiver sensitivity is mainly about the last part you mentioned (ie: how much noise the amp itself inserts while amplifying). Co-channel interference or adjacent-channel interference will of course degrade ANY signal, regardless of what the RX sens is (better band pass filters can help cut adjacent-channel interference, but that's not really directly related to RX sens levels)

Better RX sens is for sure available in consumer electronics and can work together with better antennas to help boost/improve your RX signal. For example, on my SAT-TV dish I had a LNB with a 0.7dB noise figure and was having problems receiving some channels. When I upgraded my ($10) 0.7dB LNB to a ($30) 0.3dB LNB my reception improved alot (the 0.3 refers to the amount of the noise the amp itself insets, and a lower number is better. Zero would be the best, in theory)

Also, with WiFi, I had a card rated with a min sens of -89dBm for 1Mbps, and when I upgraded to a card rated with a -92dBm at 1Mbps my range improved alot (the price difference in card was maybe $20). Every 6dB improvement is a doubling of the signal distance, so I gained a 50% increase in distance by getting a card with a 3dB lower RX sens. And it wasn't that expensive.

So I'd say to get the best range, a combo of a good antenna and a receiver with a good RX sens together is the best way to go. And if you look around you'll probably find they are commercially available and aren't that expensive. ...but I guess most people don't think about that (as per some of the discussion in this thread), they just look at TX power, since that's what they equate distance with.

[KillaGreen]

Are the Cantenna type devices worth looking into? I'm interested in knowing what kind of practical range can be achieved with a directional antenna. Be quite a cool experiment as I have a lot of open space near my apartment.


Before i say anything... is it illegal to make an antenna for your wifi stick ? and where ?

KillaGreen

[Barry]

Before i say anything... is it illegal to make an antenna for your wifi stick ? and where ?

KillaGreen

As long as you stay under the transmit power limits your country states, then I don't see why it would be illegal.

[KillaGreen]

Sweet, cause a cantenna is pretty much passive gain eh, and yeah cantenna's do work and they will increase your range, but don't expect a miracle with a can :D but you could allways attatch the can to a dish, like so many have on google, (a good size for the can I got from wikipidia was 8.5cm X 14.5cm with the hole in the can at 1.25cm from the back) all of the sizes are based on the wavelength of 2.4 GHz frequency. And a while ago i remember calculating out the proper size dish for 2.4 GHz signals, and it was roughly 3 meters! lol but don't worry because all parabolic dishes have the same focal point characteristics (but 3m would be the ideal size :P).

As for distance, people have reported distances in the km range with simply a recycled can and dish.

KillaGreen

[holyiosef]

Speakng of dishes, the AB9IL antenna projects were moved to a new URL:

http://www.ab9il.net/wlan-projects/wifi1.html

Articles for building large parabolics and helicals. The 0.8 meter TV dish works well over here, through trees, bushes, and other obstructions. Helical good too.

Also how to connect external antennas to Linksys wusb54gc and Belkin F5D7050.

[Nokii]

When searching for a wireless card, people often want to find one with the best range.
...
As 802.11b/g uses 2.4 ghz, which operates like any other radio frequency signal, we can use the basics of
RF signal propagation to determine range. There are five basic components which effect signal propagation:

*Transmit power
*Transmit antenna gain
*Frequency and distance (path loss)
*Receiving antenna gain
*Receiver sensitivity

There are other factors which effect signal loss as well: cable losses, RF opaque materials in the signal path, etc.

Because wireless communication is a two way process, we may also have to include the same five factors in reverse.
While 'transmit power' referred to your wireless card, on the return trip 'transmit power' refers to the access point.
Likewise, 'receiver sensitivity would refer to your card as opposed to the access point, and so on.
...

I'll add that there is one more thing. MIMO.

MIMO enhances NLOS (Non-line-of-sight) propagation and cancels reflections. MIMO offers significant increases in data throughput and link range
without additional bandwidth or transmit power. It achieves this by higher spectral efficiency (more bits per second per hertz of bandwidth) and
link reliability or diversity (reduced fading).

Sources:
hxxp://en.wikipedia.org/wiki/Non-line-of-sight_propagation#Passive_random_reflections
hxxp://.atheros.com/news/xspan.html
hxxp://en.wikipedia.org/wiki/Multiple-input_multiple-output

[ShadowKill]

I'll add that there is one more thing. MIMO.

MIMO enhances NLOS (Non-line-of-sight) propagation and cancels reflections. MIMO offers significant increases in data throughput and link range
without additional bandwidth or transmit power. It achieves this by higher spectral efficiency (more bits per second per hertz of bandwidth) and
link reliability or diversity (reduced fading).

Sources:
hxxp://en.wikipedia.org/wiki/Non-line-of-sight_propagation#Passive_random_reflections
hxxp://.atheros.com/news/xspan.html
hxxp://en.wikipedia.org/wiki/Multiple-input_multiple-output

I have to say Nokii, these first few posts you've made are very impressive. I'm glad to see another member of the community offering up as much as you have, and as quickly as you have. Let it be known that your participation within this community is very much appreciated and hasn't gone unnoticed....

[madferret]

Lots of great info on antennas here guys but I've found out the hard way during a brief stint in pirate radio that to get the best signal strength (ie. best propagation) you need to make sure that your aerial is at least 1 wave length off the ground and should be 1 wavelength long.

Since 802.11 is 2.4 GHZ and wavelength = speed of light / frequency

Wavelength = 299,792,458 / 2,400,000,000 = 0.12491352416666666 meters

12.49 cm = 4.9 inches

So if you want best results from your antennas make sure they're at least 4.9 inches away from the walls or desktop they're sat on (how many of us have them sat in a corner?) and ideally they should be 4.9 inches long.

Of course since each wifi channel has a slightly different frequency we could tailor an antenna to a channel:

ch1: 2.412
ch2: 2.417
ch3: 2.422
ch4: 2.427
ch5: 2.432
ch6: 2.437
ch7: 2.442
ch8: 2.447
ch9: 2.452
ch10: 2.457
ch11: 2.462
ch12: 2.467
ch13: 2.472
ch14: 2.484

Though I think we'd only be talking about a milimeter or so probably not worth it ;) .

[SLK001]

Lots of great info on antennas here guys but I've found out the hard way during a brief stint in pirate radio that to get the best signal strength (ie. best propagation) you need to make sure that your aerial is at least 1 wave length off the ground and should be 1 wavelength long.

Since 802.11 is 2.4 GHZ and wavelength = speed of light / frequency

Wavelength = 299,792,458 / 2,400,000,000 = 0.12491352416666666 meters

12.49 cm = 4.9 inches

So if you want best results from your antennas make sure they're at least 4.9 inches away from the walls or desktop they're sat on (how many of us have them sat in a corner?) and ideally they should be 4.9 inches long.

Of course since each wifi channel has a slightly different frequency we could tailor an antenna to a channel:

ch1: 2.412
ch2: 2.417
ch3: 2.422
ch4: 2.427
ch5: 2.432
ch6: 2.437
ch7: 2.442
ch8: 2.447
ch9: 2.452
ch10: 2.457
ch11: 2.462
ch12: 2.467
ch13: 2.472
ch14: 2.484

Though I think we'd only be talking about a milimeter or so probably not worth it ;) .

Absolutely, positively, NOT true (well, the frequencies and the channel numbers appear to be true).

[ShadowKill]

Absolutely, positively, NOT true (well, the frequencies and the channel numbers appear to be true).

An explanation of why not would be beneficial to those that don't know any better....

[Thorn]

An explanation of why not would be beneficial to those that don't know any better....Short answer, without going into the physics of antenna design: You use wave fractionals. Quarter-wavelength and half-wavelength antennas are very common. As long as the antenna's radiating element resonates to the wavelength it should work.

[ShadowKill]

Short answer, without going into the physics of antenna design: You use wave fractionals. Quarter-wavelength and half-wavelength antennas are very common. As long as the antenna's radiating element resonates to the wavelength it should work.

Oh no, I understand fully brother, I was speaking on behalf of those less informed and too shy/nervous/whatever to speak up.

[Thorn]

Oh no, I understand fully brother, I was speaking on behalf of those less informed and too shy/nervous/whatever to speak up.Yeah, I understood why you asked. In the same vein, I give the KISS answer, but just quoted you for the sake of continuity.

[ShadowKill]

Yeah, I understood why you asked. In the same vein, I give the KISS answer, but just quoted you for the sake of continuity.

Oh continuity, the bane of many an auditee.... Speaking of which, I need to update my continuity binder, thanks ;)

[radioraiders]

I'll add that there is one more thing. MIMO.

MIMO enhances NLOS (Non-line-of-sight) propagation and cancels reflections.
Good to mention MIMO, but that's not a necessary part of a radio link budget ("the Prez" covered the basic parts nicely in the original post). MIMO more of an "extra feature"...and remember it must be on both receiving and transmitting sides to work. If your laptop card has MIMO, but not the Access Point, it won't work. And may not always be needed (ex: in LOS links MIMO won't really give any additional benefit)

MIMO isn't required in 802.11g, but has been used in some proprietary equipment, not just to increase the range, but thruput as well since they use it to transmit/receive on 2 channels instead of just one (ie: jumping from the standard 54Mbps to 108Mbps). With 802.11n MIMO will be standard. MIMO is also being incorporated in furute releases of HSPA and is used in WiMAX.


PS- WiFi has also had a built in feature to help overcome multi-path propogation losses since it was officially released in 1999 called OFDM.

http://www.radioraiders.com/wlan-datarates.html

Since wifi channels are quite large (20Mhz) it can take advantage of that wide bandwidth by breaking the signal down and spreading the signal over the full 20Mhz. This makes it less prone to multipath fading compared to narrowband signals (like say GSM which transmits in 200khz channels).

[madferret]

I was only going of what I know about radio waves with regard to FM transmission, I figured it might apply to wifi too - obviously not. Don't be too harsh, I'm only trying to add to the discusion.

[Thorn]

I was only going of what I know about radio waves with regard to FM transmission, I figured it might apply to wifi too - obviously not. It doesn't apply to FM either. The fact that it was based upon your experience with pirate radio though, doesn't surprise me. Based on my experience, what the average pirate radio moron don't know about RF could fill several books. The real shame is that there isn't a bounty on such 'pirates'.

Don't be too harsh, I'm only trying to add to the discusion.SLK001's answer wasn't harsh. SLK001 was just stating the truth. I was being harsh above, and I admit it.

I'm only trying to add to the discusion.
You probably shouldn't add to a technical discussion if you don't know the technology. While you at least understand wavelengths, you might want to learn more on antenna design. I would suggest the ARRL Antenna Book as a good starting place.

[madferret]

You probably shouldn't add to a technical discussion if you don't know the technology. While you at least understand wavelengths, you might want to learn more on antenna design. I would suggest the ARRL Antenna Book as a good starting place.

Point taken.

[bb_EcKo]

Lots of great info on antennas here guys but I've found out the hard way during a brief stint in pirate radio that to get the best signal strength (ie. best propagation) you need to make sure that your aerial is at least 1 wave length off the ground and should be 1 wavelength long.

Since 802.11 is 2.4 GHZ and wavelength = speed of light / frequency

Wavelength = 299,792,458 / 2,400,000,000 = 0.12491352416666666 meters

12.49 cm = 4.9 inches

So if you want best results from your antennas make sure they're at least 4.9 inches away from the walls or desktop they're sat on (how many of us have them sat in a corner?) and ideally they should be 4.9 inches long.

Of course since each wifi channel has a slightly different frequency we could tailor an antenna to a channel:

ch1: 2.412
ch2: 2.417
ch3: 2.422
ch4: 2.427
ch5: 2.432
ch6: 2.437
ch7: 2.442
ch8: 2.447
ch9: 2.452
ch10: 2.457
ch11: 2.462
ch12: 2.467
ch13: 2.472
ch14: 2.484

Though I think we'd only be talking about a milimeter or so probably not worth it ;) .

I can't say that all the info you gave is correct, some of it might be. For example the height of the antenna to the ground.

http://en.wikipedia.org/wiki/Fresnel_zone