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Thread: wireless antenna array?

  1. #1
    MySQL Error soundman98's Avatar
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    wireless antenna array?

    i searched for a while and couldn't fine anything-- is it feasable to setup a array of more than one antenna for a single wireless port on a wireless card?

    if it would work, would it help at all over a single antenna setup?

    i have a convertible, so mounting the antenna in the rear windows is not a option, and it seems that the best reception area for the wireless antenna is blocking my view in the middle of the windshield...

    i currently have it mounted inside the dash, and get decent reception, but it can always be improved..

  2. #2
    Maximum Bitrate SjLucky's Avatar
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    I just got a PowerMac G4 MDD and it has a wireless b/g card in it. I am no way shape or form a mac guy. I got it cause it looked cool back to the point Upon taking it apart, (i do this for some reason I cant explain) I noticed that when I followed the wireless lead out, It connects to a little board and then splits off to two metal box looking antenna that are on both sides of the case. I'm not at the house or I would post pictures. I wonder if you could use that? I will do some snooping around.

    Whats a good wireless benchmarking program? I'll do some testing with it.
    Quote Originally Posted by menudude View Post
    thank you all for your help minus the useless post by sjlucky...

  3. #3
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    I could be wrong about this, but splitting the antenna may be a double-edged sword. My theory is that you may increase the diversity (though I don't know if it's possible since the adapter only has one antenna input), at the expense of range. The card is only able to output x amount of mW. Attaching two antennas will probably halve the output to each antenna. Best way to make the most of what you have would be using a directional antenna, but this is probably not ideal as you'd have to know where the AP is. Not so bad in your driveway, but pretty much a hassle anywhere else.

    Attacking this in the other direction would be to get a higher power adapter.

    As you already mentioned moving it outside of the dash will help also. Being so close to all those other electronics and wiring doesn't help. What kind of adpter is it? if it's USB, it's easy to move around without having to use a long, range-robbing pigtail. Since you don't have a rear parcel shelf to mount it on, what about on one the headrests (front or rear). Depending on whether you're up to some tasteful mutalation, you can mount it inside with the antenna sticking out (or completely inside), or mount it to one of the up/down shafts.

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    look up cophasing antennas. ham radio guys do it on up through vhf and uhf i think. i work with rf stuff and 50 ohm cable is what we work with. cophasing in that regard requires 50 ohm cable from the source with a double female T connector and splits two antennas with 75 ohm cable acting as an impedance transformer. the result is a gain of 3dB (double) the sensitivity of the reciever. in some instances with multiple cophasing you can actually hear farther than you can transmit. but with just two antennas and your high frequency band I don't see this being an issue. how all this applies specificically to the world of wifi I don't know. but your theory has been succesfully done by 2 way radio guys. but blackmamba is right, your effective transmit will be reduced by 3dB as well since your splitting your power into two resonante antennas. if you can somehow amplify your signal to compensate for the loss you might be in business. not that this has anything to do with your application but cophasing for recieve generally makes you more susceptible to more "noise" due to increase sensitivity.

  5. #5
    MySQL Error soundman98's Avatar
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    Hmm good to know...

    Since posting this thread, I got a different motherboard that included a USB dongle(it has a via chipset) and has 2 wifi antenna ports on the card, but only included one antenna port, so I picked up another port adapter, but haven't gotten a chance to try much-- so far, I just plugged it in and let the 2nd antenna hang out under the passenger seat with the rest of the carputer--so far it does not seem to have helped, or hurt my signal strenth in any way(though it is posible that there are 2 powered ports on this dongle)

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    to test any improvement from your second antenna, the placement is very crucial (for any antenna) i know this sounds like a simple assumption but again, you more than double your gain by moving your antenna from the floorboard of the car to the top of the car. i know no one wants to do this but i say it just for a frame of reference. next to the back window is a much more practical and useful spot.

  7. #7
    MySQL Error soundman98's Avatar
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    you might have missed this-- i have a convertible, so, while i realise that the rear window is a very good location, it is nonexistant in my car.

    i forgot to mention that i installed a 6 meter, reverse-sma extension cable for the original wifi port, and currently mounted the antenna with some velcro on the center of the inside of the front window. currently, i am getting about 5mb @ 30ft from my house network-- which pretty good for the cheap little wireless router i use. i haven't tried this setup on any other networks, and my old setup, using a wifi dongle under the dash w/ 3db antenna got just as good reception...

    i plan to eventually get another one of the extension cables, and a pair of similar 3db gain antennas(i think that it is better to have matching antenna lenths-even if it is just for my ocd), and then mount a antenna on both a-pillars. the theory is that i will be turning each antenna into a more-directionsal antenna(because the a-pillar is going to be shielding/blocking parts of it.), but using 2, can get a little broader reception.

  8. #8
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    Wow! A 6 M extenstion equals a lot of loss. I don't remember how they calculate the loss, but even with a low-loss cable and in a car enviroment, you may be looking at close to a 50% loss. I would ditch the borad's dongle, unless you can extend the usb connector for it. I would use something like this and extend it using usb. Keeping the antenna as close to the adapter as possible to minimize loss. It's small enough that you can put it pretty much anywhere. The antenna is also detachable if you want to run a short pigtail and just have the antenna sticking out.

  9. #9
    MySQL Error soundman98's Avatar
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    didn't think of the loss of the cable--then i might move the dongle to the dash, and get a much smaller extension cable.

    my carputer is under the passenger seat, and a 6' passive usb extension will reach to teh top of the dash, but the best reception spot seems to be towards the top of the windshield...

  10. #10
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    Well if there's enough room at the top of your windshield then you can go longer without any problems. Usb's max length is 15' before you need to use repeaters.

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