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There is a similar question to mine already asked, but it does not address completely what I want to know, so I am going to create a new question.

I am using long-range RF69 900MHz radios in an Arduino project of mine. I'm trying to keep this as low cost as possible. I have noticed that high-gain SMA antennas are quite expensive (about $5) as compared to just regular wire. It makes sense that I would want something specialized to transmit data. My question is if I need such an expensive antenna for receiving, or if a few centimeters of regular wire will be roughly equivalent.

The data sheet for my RFM69HCW radio specifies that with line-of-sight communications and fancy SMA antennas a theoretical range of 3 or more miles is possible. If I only utilized a 900MHz SMA antenna for the transmitter, kept the transmission strength up at around 20db, and used just a wire antenna for the receiver could I still get this range? Or is the SMA antenna just fundamentally better at receiving these radio waves as well. Thanks!

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It makes sense that I would want something specialized to transmit data. My question is if I need such an expensive antenna for receiving,

The transmit and receive antennas are equally important for determining the signal amplitude delivered to the receiver electronics.

I have noticed that high-gain SMA antennas are quite expensive (about $5) as compared to just regular wire.

In the world of antennas, "high gain" means that the antenna has a highly directional emission profile. It does not mean that the antenna is able to deliver more power into the transmission than it is provided by the amplifier that drives it.

If you want to be able to transmit or receive signals without knowing which direction the other station is in, you do not want a high gain antenna.

If you know what direction the other station is in, and can point the antenna toward it, then you want a high-gain antenna.

More likely you want to find an antenna with good electrical efficiency at the frequency you will be using. Again, the transmit antenna and receive antenna contribute equally to the overall efficiency of the link.

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