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Thread: Question about interference

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    To stop interference you really have to design it out in the first place. If you are having problems at the end of the build it is unlikely youll be able to help it much with spray on screens, or by earthing a cable or two.

    Have a look at my EMC page at http://homepages.which.net/~paul.hills/Emc/Emc.html
    http://homepages.which.net/~paul.hills/Emc/Emc.html, and also some info on the radio page here: http://homepages.which.net/~paul.hills/Radio/Radio.htmlhttp://homepages.which.net/~paul.hills/Radio/Radio.html. Theres also a good document here: http://www.technobots.co.uk/technical/guidance/EMI%20and%20how%20to%20deal%20with%20it.pdfhttp://www.technobots.co.uk/technica...o%20deal%20wit h%20it.pdf

    In short, here are the main points, in order of importance (most first):

    1. Isolate the radio & low power electronics from the power stuff. That means use separate batteries for each, and make sure the drive signals to the speed controller use opto-isolators. Dont use Battery Eliminator Circuits (BECs).

    2. Make sure the antenna is the right length, and is properly connected to the receiver using the correct cable. Dont use any old wire, make sure the antenna is as far as possible away from other metallic parts of the robot. Dont shield the antenna under the metal armour!

    3. Keep the antenna and receiver away from cables carrying large currents, and the motors.

    4. All the other tips in the documents identified above!

    Cheers & good luck!
    paul

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    To Answer your question you should connect the Earth screen to the chasis at both ends and also connect your Rx battery earth to chasis but dont connect the main battery to chasis. At least thats the way we did it. In effect the Rx & Rx battery is also in a metal box so that the Rx circuit is completely enclosed with a screen from the rest of the wiring, less the wires to the speedos through opto-isolators.

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    Ah, now I remember, thats what I was told as well.

    Only reason why its earthed at both ends is because the rx Areial is connected through a SMB connector to a coax cable to bring it out of the metal box and hence the box is earthed through this connector. The coax then winds its way past the removable link and all the power wires through the middle of a moving sprocket into the arm. To create a 1/4 wave Dipole Areial the earth must be connected to a ground plate (chasis) at the point where the Areial leaves the coax cable. It would have been better if the ground plane was not already earth but connecting the areial to the rx with 50ohm coax to this areial gives approx (If I remember my areial theory) 50ohm also giving the best matching without additional components. The problem comes from not knowing the impedance of the Rx which is probably not 50ohms so there is a mismatch there with could casue problems.

    The Rx after all is designed for a single wire areial. There are many possibilities and basically I used the old EMC trick, guessed, and it worked for us.

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