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I have a radio transmitter (for my quadcopter) and I wanted to improve its range. So for now I removed its integrated antenna and I soldered a male sma connector so I can plug in any antenna I want. I was thinking to add one more antenna. Keep in mind that the transmitter has only one antenna. So adding a second antenna will be something like this:

schematic

simulate this circuit – Schematic created using CircuitLab

Basically the second antenna will be connected to the first one. I would like to know if adding the second antenna will be better, worse or simply the same.

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    \$\begingroup\$ Depends on the impedance of the antennae AFAIK - can't tell without giving us some more info about the antennas (e.g. the length of the antenna and the frequency of the radio link). \$\endgroup\$ – Morten Jensen Mar 16 '17 at 15:03
  • \$\begingroup\$ @MortenJensen 2.4GHz \$\endgroup\$ – DimChtz Mar 16 '17 at 15:04
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    \$\begingroup\$ It is not easy to connect two antennas to one transmitter to get a better result. It is very likely that the result will be much worse. It is especially difficult for frequencies in the GHz area. Without very sophisticated equipment and a deep insight to antenna theory, it is impossible to get a better result. The insertion of a sma connector pair and additional may impair the matching of the antenna to the transmitter. \$\endgroup\$ – Uwe Mar 16 '17 at 15:30
  • \$\begingroup\$ A single antenna-with-gain will give increased apparent transmitted power but only if you point it at your 'copter. Otherwise, it will give less power. Too much to do (fly & point at the same time). \$\endgroup\$ – glen_geek Mar 16 '17 at 16:07
  • \$\begingroup\$ Need a spotter with Yagi antenna if you want longer range. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 16 '17 at 16:17
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An antenna's impedance is matched to the transmission circuit in order to produce the best output level (within regulatory rules). Putting two antenna's in parallel at best shares the power. At worst, they together get half the power and even worse they may produce fields that cancel each other's transmission and you get very little transmission distance.

You might get lucky with some antennas and get an improvement but that improvement will be more directional than with a single antenna. This may prove problematic in itself because you have to be facing the quadcopter more precisely than before (and it may still break regulatory rules).

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  • \$\begingroup\$ Does this mean that I shouldn't even remove the integrated antenna? \$\endgroup\$ – DimChtz Mar 16 '17 at 16:03
  • \$\begingroup\$ You can remove it but I wouldn't take the risk of trying to transmit without an antenna because this might destroy the output transistors in the power amplifier that feeds the antenna. \$\endgroup\$ – Andy aka Mar 16 '17 at 16:05
  • \$\begingroup\$ quadquestions.com/blog/2015/06/15/long-range-fpv-setup \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 16 '17 at 16:15
  • \$\begingroup\$ @Andyaka No, I removed the integrated antenna just to put an sma connector so I can use any antenna I want. Not to leave the transmitter without an antenna. \$\endgroup\$ – DimChtz Mar 16 '17 at 16:16

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