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My USB WiFi adapter has two antenna connectors, I have a lack of knowledge of these connectors, few questinos:

  • how to check which connector is 2.4/5 GHz or both are 2.4/5 GHz at the same time?
  • comes with these two antena, as I see its a 2.4 GHz antenna, then why vendor gives me two 2.4 GHz antennas without 5 GHz antenna?
  • I could connect to one connector 2.4 GHz antenna and to the second connector 5 GHz antenna?
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    \$\begingroup\$ Can we have the specs for the USB WiFi adapter? There is no useful context here... \$\endgroup\$
    – mhaselup
    Nov 2 '20 at 0:50
  • \$\begingroup\$ for example this one \$\endgroup\$ Nov 2 '20 at 0:52
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    \$\begingroup\$ Both antennas do both frequencies. \$\endgroup\$ Nov 2 '20 at 1:01
  • \$\begingroup\$ Since 5 GHz is 2 x 2.5 GHz, a 2.5 GHz antenna can work well enough on both frequency bands. \$\endgroup\$ Nov 2 '20 at 8:02
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    \$\begingroup\$ @Bimpelrekkie: Actually 2.4 and 5.8 GHz for 802.11ac, not exactly an harmonic, and the antennas probably don't work in λ/4 or λ/2. \$\endgroup\$
    – mins
    Nov 2 '20 at 11:39
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The USB Wifi adapter you mentioned has two antennas. Each of these operates on both 2.4 and 5GHz bands per the specification-"2.4G/5GHz Dual-Band 5dBi dipole antenna".

The reason you have 2 antennas is to enable the MIMO/beamforming/multiple concurrent transmissions capabilities as defined by 802.11ac

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In antenna deisgn, you have something called standing wavelengths where you have a zero crossing at each wavelength. 2.4Ghz is close to 2.5 or half of 5Ghz and an antenna can be tuned to operate at both frequencies. There are many antennas though that can't do both so I'd look at the datasheet to make sure. From what you showed that antenna should be able to work on both 2.4 and 5 GHz channels, do you have two different connectors that are labeled 2.5 and 5Ghz?

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  • \$\begingroup\$ there is some disassembled pictures, connectors are not labeled as 2.5 or 5Ghz \$\endgroup\$ Nov 2 '20 at 1:03
  • \$\begingroup\$ Here is alfa 2.4 GHz antenna. Specs: Frequency 2400 ~ 2500MHz, then this can be tunned to operate on 5 GHz? \$\endgroup\$ Nov 2 '20 at 1:11
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    \$\begingroup\$ @TheAnotherWise why don't you pick one of the antennas explicitly spec'ed as dual-band? alfa.com.tw/products_detail/136.htm for example? \$\endgroup\$
    – the-wabbit
    Nov 3 '20 at 15:29

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