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...it has to do with the 'Magic' as you referred to it in another post.. the dimensions, are only part of the how an antenna works.. typically the antenna sold on Ebay, Amazon, BangGood or 'Other UAV' websites only spec out at around 1.7 to 2.0 VSWR and the the 'Tuning' varies
Wildly thats why one may work half @$$ whereas another doesn't or barely works at all and the reason they're sold and continue to sell is, like you also pointed out in another post is most people don't have the means to test or measure the antennas performance.. I am currently in development of an antenna system designed specifically for our drones and hope to have it out 1Q2017, proof of concept has has been very promising out to at least 6000ft over heavily WiFi congested areas and thats with Antennas Only.. my antennas and/or systems will include a spec sheet, detailing the Band-Width, Return Loss and VSWR.. some of the testing and nfo on this subject can be found on my website (Equip, Phantom Tab)...
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...also I've recently purchased a batch of antennas, I will Hand Tune Each of them, and sell them as a set included with a spectrum analysis data sheet, I'll have 6-8sets avail.. if anyone is interested you can use this Forum or use the following email address SAS (at) GasRecovery (dot) net...
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IIIDaemon
www.GasRecovery.net