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I need to know the approximate direction of the radio signal coming to my module, and I have to use very simple hardware and software for this. (Just a microcontroller and one module)

What came up to my mind was using more than one directional antenna with the module, each looking at a different direction, and have a rough idea of where the signal is coming from, by comparing the RSSI of the arriving signal for different antennas.

Is this possible? If so, how can the module switch between different antennas without using mechanical means?

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  • \$\begingroup\$ Instead of depending on RSSI. You should depend on phase shift which corresponds to a time delay. Then you will be able to narrow it down with much higher precision. \$\endgroup\$
    – Harry Svensson
    Oct 7, 2018 at 12:19
  • \$\begingroup\$ What is your goal? what signals and why 2 antenna \$\endgroup\$
    – Tony Stewart EE75
    Oct 7, 2018 at 14:13
  • \$\begingroup\$ WHy use simple hardware when sophisticated dual channel digital tuners exist that are low cost? \$\endgroup\$
    – Tony Stewart EE75
    Oct 8, 2018 at 15:36
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    \$\begingroup\$ @TonyEErocketscientist, for two reasons; first because I didn't know these products, second, my project is kind of IoT project and may not justify the cost and size of such products. \$\endgroup\$
    – Eesan Hzmi
    Oct 8, 2018 at 19:35

2 Answers 2

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Forget RSSI, I don't know why anyone thinks it is a sane idea for this sort of thing, but it keeps coming up.

Instead, use 4 aerials, an FM receiver module and 4 pin diode switches (Or the equivalent packaged up by someone like skyworks), you drive the switches in quadrature and thereby cause the effective antenna position to move in a circle, this produces Doppler shift which the FM recever demodulates as a sine wave, the phase between the recovered sine and the antenna switch drive gives you bearing.

This is sensitive to multipath, but much less so then RSSI based sillyness.

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    \$\begingroup\$ I have searched the internet in the meanwhile, and couldn't find a practical example doing that (a diagram of a 4 aerial/diode antenna circuit and a software calculating the doppler shift), other than theoretical explanations, which was the first reason I was going the simpler RSSI way rather than the phase shift I am not knowledgeable about. Secondly I don't know if my project can justify the cost and size/power requirement of a Doppler shift, and RSSI seemed possible because I have more than one radio sources which I thought can compensate for the positioning errors of each other from RSSI. \$\endgroup\$
    – Eesan Hzmi
    Oct 8, 2018 at 19:29
  • \$\begingroup\$ @EesanHzmi I have seen several designs in the Ham radio literature. \$\endgroup\$
    – Dan Mills
    Oct 8, 2018 at 19:45
  • \$\begingroup\$ @DanMills Do you mind.. showing at least one of them? \$\endgroup\$
    – Harry Svensson
    Oct 9, 2018 at 7:13
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    \$\begingroup\$ @HarrySvensson Here is some stuff, and more importantly links to some of the classic designs (SDR NOT required), you would need to play some games to use the frequency error data from that RFM69, but it might be workable. wiki.spench.net/wiki/SDRDF \$\endgroup\$
    – Dan Mills
    Oct 9, 2018 at 10:52
  • \$\begingroup\$ Found some drawings as you have suggested: link link This guy has written an arduino code : link The link is not working however. Generally it looks simple, but I am having difficulty in understanding what is going on I guess because I am not familiar with the subject. \$\endgroup\$
    – Eesan Hzmi
    Oct 9, 2018 at 19:46
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Rev B

An active RF switch, often used for Diversity ( direction) or Rx/Tx or SP2T , SP3T, SP4T etc. comes in all sizes, shapes, BW, power levels and performance specs.

enter image description here e.g. Infinion: BGS12PL6 General purpose RF CMOS power SPDT Switch in ultra small package with 0.77mm 2 footprint < $0.20 (10kpc)

With the right tools: hardware, software, you can test any radio on a turntable, a good Test Engineer can get plots like this using your RSSI signal with its calibration formula from the OEM of the Radio Chip or chipset.

enter image description here

IoT product selector

Thus you can get the best gain from multiple antenna.

Or you can spend a little more $4 (@ 450 pc) and get something almost omnidirectional from guys like Linx with a compromise in diversity gain reduction. enter image description here

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  • \$\begingroup\$ Is this better @DanMills ? \$\endgroup\$
    – Tony Stewart EE75
    Oct 8, 2018 at 21:32
  • \$\begingroup\$ It seems there is a ratchet effect on votes @W5VO . why? \$\endgroup\$
    – Tony Stewart EE75
    Oct 9, 2018 at 16:53
  • \$\begingroup\$ Thank you very much. Found out that direction finding, based on RSSI is a topic of academic research, and theoretically it can even be done by a single fixed antenna : arxiv.org/pdf/1706.09690.pdf . Must learn what this multi-mode antenna is however. \$\endgroup\$
    – Eesan Hzmi
    Oct 9, 2018 at 19:50

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