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I want to use a low cost 433Mhz module for low distance domestic usage, but I need to solder an antenna , (there is a place for that on the reception module), to get a better signal across my walls. how to choose its length ?

I guess a simple wire of X% of wave length ?? or another calculation ? or is this more complex & I need something more like an old radio antenna ?

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  • \$\begingroup\$ If you can choose a different radio type, you may have more luck with your project. The crude SAW transmitter and regenerative receiver 433 MHz solutions are tricky to work with as the receivers are so noisy, while the better SPI-interfaced data radios for 433 MHz cost several times what the comparably featured nRF24-compatible 2.4 GHz modules do. Also in many places use of the 433 MHz has substantially more limiting regulations, especially with regard to allowed purpose. \$\endgroup\$ Commented Oct 25, 2018 at 16:26

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I guess a simple wire of X% of wave length ?? or another calculation ? or is this more complex & I need something more like an old radio antenna ?

Start with a quarter wave wire (circa 17 cm long) and if you get adequate reception you may experiment by shortening it a little bit but you'll find certain things if you shorten it too much: -

  • The signal level received rapidly falls away with moderate shortenings from one-quarter wavelength
  • The impedance becomes capacitive and this can be somewhat alleviated with base loading with an inductor to series tune out the capacitance.
  • You will start to make an antenna that is more optimized for higher frequencies and these may overload your receiver circuit if they are present in your area.
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    \$\begingroup\$ depending on the antenna types, their relative orientation is important, for simple wire antennas you generally want them to parallel to each other to get the best coupling with vertical orientation to earth preferred. For way more info than you probably need you can google "1/4 wave antenna pattern". Most of the stuff said is accurate, and the people who tend to have the most practical experience are going to be Amateur Radio operators, you may be able to find a local one for advice on your requirements. \$\endgroup\$
    – user201365
    Commented Oct 25, 2018 at 12:17
  • \$\begingroup\$ Thank you all I'll do that soon, wit a 17cm long antenna :) \$\endgroup\$
    – user201301
    Commented Oct 25, 2018 at 15:49

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