How to find the direction of target in complex environment?

sk001 said:

Hi!

I am trying to make a device that can find the direction of the target. My idea is to set a signal transmitter on the target, and use a microcontroller to control the motor to rotate the signal receiver so that I can find the direction with the highest signal intensity.

But I don't know much about antennas, is this method feasible? Or is there better way?

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Papabravo said:

The answer is a bit complex. It depends on the frequency of the transmitter/receiver. Higher frequencies mean a smaller lighter antenna, but more difficult to design electronics. Lower frequencies mean simpler electronics but larger, more difficult to articulate antennas. I'm not sure there is a happy medium where you can do this legally without a license.

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rjenkinsgb said:

With a single antenna it's often easier to have a screen behind it and find a null, rathe than try and find the peak.

With four antennas and diode switching, you can use doppler principles - sequentially switch each antenna to an FM receiver and you get and audio tone at the "rotation" frequency. The phase of that relative to the switching phase tells you the direction of the transmitter.

An example design:

Version 2.3 Doppler RDF

By the end of the year 2011 I started the development of the PA8W Doppler Radio Direction Finder. Wherever possible I used available knowledge found on the internet. I studied, filtered, adapted an…

radiodirectionfinding.wordpress.com

(If you have ever noticed that some police cars have a cluster of four identical antenna on the roof - that's a similar setup using the same basic concept, for locating stolen vehicles with "Lojack" style transmitters fitted to them).

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sk001 said:

Thank you!
I'm a student, and this is a little thing I'd like to make. Maybe don't need to worry about liscence. I just want to make sure this method works and then I can start to learn antennas and build it myself.

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Papabravo said:

I would not be so cavalier about doing RF experiments without a license, unless you have somebody willing to take the rap for you. Believe me when I tell you do not want to be called in front of a federal judge to defend yourself against a potential charge. At least familiarize yourself with the requirements for operating in the frequency band you intend to use. As a student YOU are responsible for your actions, and your professor is probably not.

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