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Thread: Wireless Range

  1. #41
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    Quote Originally Posted by SLK001 View Post
    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.

  2. #42
    Senior Member streaker69's Avatar
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    Quote Originally Posted by anathema View Post
    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.
    A third party security audit is the IT equivalent of a colonoscopy. It's long, intrusive, very uncomfortable, and when it's done, you'll have seen things you really didn't want to see, and you'll never forget that you've had one.

  3. #43
    Very good friend of the forum hhmatt's Avatar
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    Quote Originally Posted by streaker69 View Post
    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?

  4. #44
    My life is this forum Barry's Avatar
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    Quote Originally Posted by hhmatt81 View Post
    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.
    Of course, if you really wanted to have some fun, go to Wal-Mart late at night and ask the greeter if they could help you find trashbags, roll of carpet, rope, quicklime, clorox and a shovel. See if they give you any strange looks. --Streaker69

  5. #45

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    Quote Originally Posted by SLK001 View Post

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

  6. #46
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    Quote Originally Posted by radioraiders View Post
    ...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.

  7. #47
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    Quote Originally Posted by SLK001 View Post
    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.

  8. #48
    Very good friend of the forum drgr33n's Avatar
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    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

    Quote Originally Posted by ebay ad
    Low noise RX amplifier is used to pick up weak signal at optimal Signal-to-Noise Ratio (SNR).
    Quote Originally Posted by danets website

    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

  9. #49

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    Quote Originally Posted by balding_parrot View Post
    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.

  10. #50
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    Quote Originally Posted by SlingShot View Post
    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

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