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I want to work with amateur, low power, and/or pico satellites. I would like to use an Eggbeater or Turnstile antenna with my UHF 433 MHz radio, since those antennas are very cheap and easy to build and I don't have to care about yagi rotors. The space for the antennas is also limited.

I would also like to use an LNA next to the antenna, but I don't know how to bypass the LNA when transmitting. I know I need some sort of switch or relay, but I can't seem to find something useful in Google. I don't mind soldering something and building some filters!

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    $\begingroup$ I don't have an answer for you, but in case it helps your research, that type of switching is called a "T/R switch" or "T-R switch", standing for “transmit/receive”. (It can be done either from a control line from your radio, or by sensing the RF power; the latter is simpler to hook up but requires the LNA output to survive the reverse power until the switch activates.) $\endgroup$ – Kevin Reid AG6YO Apr 6 '16 at 16:44
  • $\begingroup$ Google for Bias Tee and you'll see that putting a DC offset on the transmission line can be used to switch a relay out in the field. This is how we use switching between two beverage antennas that are at least 50m away from the shack. $\endgroup$ – captcha Apr 7 '16 at 22:18
  • $\begingroup$ Scratch around the EME / moonbounce websites. They all have pre-amplifiers and high power transmit amplifiers, and they describe the switching systems to make this work. $\endgroup$ – tomnexus Apr 29 '16 at 4:50
  • $\begingroup$ Some hams at stationproject.wordpress.com/2014/05/16/… have described the switched LNA system used for their satellite communication systems. $\endgroup$ – user2943160 Jun 6 '16 at 2:25
  • $\begingroup$ yu1cf.com/Cheap-High-Power-50-144MHz-Relay $\endgroup$ – Phil Frost - W8II Sep 20 '16 at 22:50
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If the antennas are cheap and easy to build, why not build two and use one for TX and one for RX, then use a common RF sense antenna switch such as MFJ-1707 to switch between the two. This allows you to have one coax to your transceiver and two antennas. Control lines for switching are also accommodated in many of these types of antenna switches. Typical of these types of switches is to also have auxilliary "switch to ground" ports which you can use for other fun stuff, such as isolating your LNB by de-powering it, assuming the LNB is at the antenna and not at the radio.

Additionally, if you enjoy antenna experimentation like I do, it's a nice way to compare different RX and TX antennas for their suitability/gain/performance, etc.

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