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Is it possible to have two antennas connected to the antenna port of an RF transceiver through some sort of mux? I want to be able to switch to a different antenna if the signal is weak on one. I would just use two of the RF modules but they are somewhat expensive.

ant2-----------------------------                          |---------|
                                 \________|2:1MUX|_________|RF module|
ant1-----------------------------/                         |---------| 

edit: this will be for a 500-900Mhz system and both antennas are oriented differently, the case isn't that one antenna is high gain and the other not.

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    \$\begingroup\$ Knowing the frequency of interest would go a long way in getting a relevant answer. Some things that work great at HF and below ( < 30MHz ) don't work well at UHF and microwave ranges ( > 300 MHz ). \$\endgroup\$
    – W5VO
    Commented Apr 1, 2010 at 3:06
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    \$\begingroup\$ Some RF modules will automatically control the antenna choice in per-packet real-time for you! The feature is called "antenna diversity" and the switching part is called a "diversity switch". \$\endgroup\$ Commented Sep 22, 2012 at 9:41

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What you're probably looking for is a SPDT RF switch of some sort. You can find RF relays that are designed for low loss and good isolation. These are usually a few hundred dollars, but you may be able to find one on ebay or surplussed for cheap. The driving of a relay is very straightforward, but may require higher voltages than anything else in your system. Another option is using PIN diodes to act as RF switches. I'm not familiar with actual applications, but it may be easier or cheaper to try and make a switch.

At the frequencies you're interested in, a simple mechanical relay may give you issues with loss and isolation. I'm also guessing you couldn't manually swap out the antennas either. Good luck.

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  • \$\begingroup\$ the SPDT RF switch seems to be what I am looking for. Here is a great app note I found: AVR2021: AT86RF231 Antenna Diversity www.atmel.com/dyn/resources/prod_documents/doc8158.pdf \$\endgroup\$
    – stbtra
    Commented Apr 8, 2010 at 5:56
  • \$\begingroup\$ I would not use a mechanical switch, but I do suggest the SPDT RF switch, I have used them before, they are easy to have running in very little time. Like all things, match your impedance. \$\endgroup\$
    – Kortuk
    Commented Apr 19, 2010 at 9:50
  • \$\begingroup\$ For a receive-only application, diode switching is probably sufficient and far less expensive. \$\endgroup\$ Commented Nov 29, 2012 at 22:31
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If you don't specifically need the different reception patterns provided by the different antennas it may be an option to use the single high gain antenna and a switched attenuator.

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Why wouldn't you just have the high gain antenna connected all the time?

There are some reference designs for Chipcon (now TI) radios that have a co-ax connector and a PCB F antenna on them. The design is meant to be used with one or the other. IIRC you install jumper resistors or replace a balun. These designs are hardwired not meant to be switched based on signal strength.

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    \$\begingroup\$ I meant two identical antennas oriented differently so one would be better suited to certain polarizations. \$\endgroup\$
    – stbtra
    Commented Apr 1, 2010 at 6:00
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I've used an RF switch from Skyworks for these purposes. The following is a nice app note from TI about doing it that explains a lot:

http://www.ti.com/lit/an/swra317/swra317.pdf
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