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I have some LoRa SX1278 433 MHz modules:
LoRa SX1278

However, I don't have an antenna. My question is: what would be a good antenna option for longest range? I don't really care that much about transfer speed, I will only be sending commands and numbers.

Is it possible to build an effective antenna from inexpensive materials? For example, can I just solder a 34.5 cm (1/2 wavelength) wire to the "ANT" pin on the module? Or is there an easy way to make a dipole?

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    $\begingroup$ "best" is still in your question. There is no "best" antenna for range. There might be several good ones for a specific geometry and situation, but your question is too vague even for that. $\endgroup$ – user10489 Jun 27 at 23:59
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    $\begingroup$ You'll probably find a recommended antenna that can be printed on a PCB in the datasheet. $\endgroup$ – Phil Frost - W8II Jun 28 at 2:04
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    $\begingroup$ The simplest antenna would be a dipole (quarter wave on each side of the coax) or a j-pole. Both could easily be printed on the pcb or made out of a wire. j-pole is end fed with a simple matching section. Both of these need both sides of the connector, neither have advantages for range. $\endgroup$ – user10489 Jun 28 at 11:23
  • $\begingroup$ @tomnexus Thank you, your editing was very much appreciated! I was kind of burned out from a lot of other mod work yesterday. :-) $\endgroup$ – Mike Waters Jun 28 at 20:49
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    $\begingroup$ Note the u.fl connector in the corner. You can buy antennas that connect there. $\endgroup$ – tomnexus Jun 28 at 21:57
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You can build an effective antenna with a quarter wave of wire sticking out from the PCB. This is called a monopole antenna.

At 433 MHz, ${1\over4}\lambda$ is about 17 cm.

The wire should be oriented straight up, so that it radiates all around it.

Monopoles require a ground plane. Your PCB and its wiring harnesses will function as a ground plane if they're fairly large - say a total of 30 cm diameter. If the board is very compact, then it will be better to build a dipole antenna instead.

A dipole can be made by soldering a 17 cm wire to the ANT pin, and another 17 cm wire to the associated GND pin, with the ANT wire going straight up, and the GND wire going straight down.

An antenna like this, monopole or dipole, will give you pretty good performance.

You should package your antenna in a way that no-one can accidentally touch the ANT wire - the module could easily be damaged by electrostatic discharge.

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