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I've seen a lot of videos and tutorials on using the Quadrifilar Helix Antenna for receiving signals, but I haven't seen any material for transmitters.

I'm just starting right now, but can a QFH antenna be used to transmit? Will it make sense for me to make one right now for receiving and then transmit from the same once I have my license?

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  • $\begingroup$ I am curious why you chose the QHA. Would you, please, tell us your application so we can learn about the uses of this interesting antenna? $\endgroup$ – Brian K1LI Aug 9 at 23:57
  • $\begingroup$ @BrianK1LI so, the QFH is supposedly an excellent antenna for satellite reception since it's truly omnidirectional for 180 degrees. I was thinking of using it to listen to 2m sats, and later when I get my license, use it to tx as well. $\endgroup$ – Amin Shah Gilani Aug 10 at 14:51
  • $\begingroup$ I understand, thanks for the info. The tradeoffs between cost of antenna, TX power, pointing system, etc. to meet the satellite's link budget are very interesting. $\endgroup$ – Brian K1LI Aug 10 at 15:08
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A key characteristic of antennas is that they are reciprocal.

That means it does not matter if you consider them in receive or transmit mode because both have the same characteristics. Changing that view often helps when wrapping your head around antenna topics.

That also means you can use any (passive) antenna for both, receiving and transmitting.

Some boundary conditions to keep in mind:

  • At circular polarized antennas when they are used in the receive as well as the transmit path that the polarization is aligned (otherwise there are considerable losses), see e.g. answer from jcoppens
    When one of them is linear polarized you get the advantage of not bothering with orientation.
  • "Some receive antennas can't be used for transmit because they can't handle the power or their SWR is poor (which is not as important for receiving)." - contributed by user10489 in the comments.
  • High gain antennas may yield to exceed the allowed EIRP in transmit mode (when the amplification is not aligned accordingly), whereas at receiving they can be used legally.
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    $\begingroup$ Reciprocity is important, but some receive antennas can't be used for transmit because they can't handle the power or their SWR is poor (which is not as important for receiving). $\endgroup$ – user10489 Aug 10 at 0:04

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