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Thread: Tap into the OEM radio antenna for WiFi?

  1. #1
    Newbie Wilco's Avatar
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    Question Tap into the OEM radio antenna for WiFi?

    It seems like something that would work, but I'm not familiar with the nuances of wireless communication. I'm guessing that the design of the antenna may not be optimized for the spectrum that WiFi uses (especially for transmission), but aside from that are there any other implications? Better yet, has anyone actually done/tried this?

    Or am I completely off-base with this even being possible?

  2. #2
    Newbie Wilco's Avatar
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    I ran across this on wifihorizon.com which seems to suggest that antenna length would be a factor:

    Wavelength and antenna length go together.To oversimplify, the longer the antenna, the more of the signal it can grab out of the air. Also, antenna length should be in whole, halves, quarters, eighths, and so on of the intended wavelength for best signal reception. The highest reception qualities come from a full wavelength antenna.
    I wonder if this goes both ways (can an antenna be too long?) or if this simply means there's a minimal length depending on the application and/or wavelength? Obviously I'm stumbling around in the dark on this one, so feel free to set me straight if I'm missing something.

  3. #3
    FLAC SNOtwistR's Avatar
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    Completely different frequencies. The shark fin does a few different things but not am/fm SNO

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    Confusion Master
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    Car aerial lengths are usually tuned for the specific frequencies they would expect to pick p, ie FM.


    WiFi would require totally different frequencies and hence a different length.

  5. #5
    FLAC SNOtwistR's Avatar
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    I remember in the old days the optimum length for the mast of am/fm was 35" or close to it

  6. #6
    Constant Bitrate
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    The 1/4 wave length of a fm antenna is around 20 inches. Wifi is much shorter but there are other things to consider. WiFi transmits and receives and antennas need to be tuned properly, if not standing waves can reduce the efficiency of the system and reduce performance.

  7. #7
    Variable Bitrate Wayne613's Avatar
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    I did it for a time on mine, I bought solderable female motorola ends to adapt to it. As suggested, not worth it. I ultimately just ran a cable to my drivers side molding to mount an 7db d-link antenna internally, which is still choked out as it's internal to the car now, but still better than trying to use the FM mast.

    The SWR(Signal to Wave Ratio) with this way off setup, relfects a massive amount of the signal needed to make a decent connection to anything not practically right next to the car using something like this. If you could get an FM antenna that was close to some usable deriviative of the 2.4ghz band used, then it might not be super-crap. In nearly any case, without it being truly setup for it, this will be a serious strain on the wifi chip/card/stick since having it be that far off reflecting that much of the TX signal translates to heat, as well as crappy connecting ability.

    In nearly any setup I'd say an internal one hidden somewhere would work better.

    You could do this "well", if you were willing to yank the entire FM mast and cabling out to replace it. As not only is the antenna wrong, but the cabling is also wrong (RG-50something I think). Which I comtemplated, but I instead hooked up an FM/SECAM TV card, and made the adapter for that. Which again, works fine for FM, but the TV band is a bit further up, so it's mediocre at best, but I still get the channels that I want when stationary, and there is nothing trying to actually transmit on it out of band now.
    Last edited by Wayne613; 07-29-2011 at 04:37 PM.
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    Newbie Wilco's Avatar
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    What about a satellite radio antenna? I've seen a lot of antennas for sale that are marked as both satellite radio, GSM, and WiFi capable. Do these just have multiple integrated antennas, or do they have enough in common that a single antenna is possible? I only ask because rumor has it that my vehicle has the sat antenna installed but not connected to anything.

    I'll have to research what frequencies sat radio and GSM use, but if anyone happens to know already feel free to set me straight.

  9. #9
    MySQL Error soundman98's Avatar
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    i believe they have 3 different antenna's in them.

  10. #10
    Variable Bitrate Wayne613's Avatar
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    Quote Originally Posted by soundman98 View Post
    i believe they have 3 different antenna's in them.
    Yes, all separate line connections.

    If you have a factory satellite antenna, again it's only really usable for that. BUT, likely the hole made for it will fit one of the after-markets that can do what you're after. I did consider doing this for mine as well, since I have a now dufunct Sirrus factory box in my trunk wall, tied to a mounted antenna drilled through the trunk lid.
    Last edited by Wayne613; 08-16-2011 at 10:35 AM.
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