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Thread: Antenna comparison: 2dBi and 5dBi

  1. #1
    Join Date
    Nov 2010
    Location
    Miami, Florida
    Posts
    16

    Post Antenna comparison: 2dBi and 5dBi

    I just wanted to post some recordings I've made after purchasing a replacement 2 dBi antenna after it was lost. I also got a 5 dBi dual-band antenna, just out of curiousity to see how it would affect the readings.
    So this is a comparison of a recording in the exact same location, one after the other (I only have one Wi-Spy so I couldn't do simultaneous). I also ran the same test on 5ghz, but the results were near identical.

    2 dBi antenna

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    5 dBi antenna

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    The most obvious difference I can see is the 5 dBi antenna picks up weaker signals at a higher amplitude than the 2 dBi. The strongest signals have higher peaks on the 5 dBi, and there seems to be a lot more peaks. It looks like the 5 dBi might have a higher resolution, but I think it just picks up individual peaks more clearly, while the 2 dBi shows more of an average.

    I didn't expect the 2 dBi showing more background noise, though. I expected a lot more noise on the 5 dBi. But like I mentioned earlier, it could just be that the 5 dBi picks up the source of the background noise more clearly so they look like peaks instead. Also, the 2 dBi picked up more noise near 2.5 ghz.

    The two or three lines that seem to be moving sideways is the same source on both recordings. While I do not know exactly the source (assuming wireless camera), it is a signal that has many peaks which are constantly moving from left to right, like a treadmill or spiral. The 5 dBi antenna shows it as a much stronger signal, at about -45 dBm. The smaller antenna reads it at only -60 dBm. I don't know why the 5 dBi antenna has three of these lines, except that it's probably be the start/end of one of the waves moving left to right.

    So, to summarize, I believe the stronger 5 dbi antenna is better suited for picking up weaker signals at a higher resolution, but trends or averages are not as obvious, because they show as individual peaks.
    The default 2 dbi antenna shows a better overview of the mid to strong signals by showing an average rather than each individual peak.

    That's my take on it, but I'd love to hear from others
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    Last edited by Soylent; 03-28-2012 at 01:18 PM.

  2. #2
    Join Date
    Sep 2011
    Location
    Boise, ID
    Posts
    188

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    Soylent,

    Thanks for posting this. Let's look at antennas like a balloon. The way in which antennas are measured (in dBi) is talking about antenna gain. This is obvious as higher dBi, the further it can go right?

    Well, if you think of an antenna like a balloon, think of it this way. The air in the balloon is the same as the power being delivered to the antenna.

    Since you are mounting the antennas to the same product, the power being put out to the antenna is the same. So, the air in the balloon is the same.

    Since both the balloons have the same amount of air, the only way to get them to reach further (have a higher gain/higher dBi) you have to squeeze the balloon right?

    The more you squeeze the balloon, the further it can reach, but the less total area it covers right? So, you increase the dBi, you increase the antenna's range, but you lose the amount of total area it covers.

    This is the trade off with antennas. If you increase the total gain, you decrease the total area covered. It doesn't matter how much power you put into it either. If you have a balloon and another balloon that is squeezed, adding air only adds to the distance the balloon covers right? So, more power equals more gain, but doesn't affect the total coverage at all.

    So with that long analogy out of the way. The 2dBi antenna will be better at covering a wider amount of total area, but won't pick up on those weaker signals; whereas, the 5dBi antenna will have less total area coverage, but will be able to reach those weaker signals.

    I hope that makes sense haha.

    Stephen

    P.S. I gave you some rep for this. This is a good post.

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