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I have a project where I need to run stepper motors within a few centimeters of wireless RF transmitters and receivers. On the breadboard I have experienced some strong interference. I am purchasing shielded wire so that I can avoid it but I am concerned about how effective my shielding will be.

I will have fully shielded wire running from the stepper to the driver but I am concerned about the open soldered connections to the board. Will this also cause interference?

I also will have to attach this shielded wire to the unshielded wire coming out the the stepper. I will make sure I do this as close to the stepper as possible but there will inevitably be some un shielded wire.

Is there anything I can do to further avoid interference at these connection points or am I being nitpicky and it won't matter to much?

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    \$\begingroup\$ Show us your driver circuitry. What speeds are you commutating the motor at.... \$\endgroup\$ – Trevor_G Mar 9 '17 at 20:31
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The radios will perform well as long as you do not overload the first transistor amplifier (the LNA). That means run lots of current through that transistor. Also, do not share GROUNDS with the motors or power drivers, even inadvertently; thus avoid Efields and Hfields coupling into Radio VDD or Radio Ground. Another trick is to use LOW Data Rates, so motor transients are short compared to a radio data-symbol duration.

The shielding effectiveness of cable strongly depends on the percent-coverage of the cable-shield; thus a foil-shield should capture more of the electric field.

For magnetic shielding, you need the magnetic fluxes to CANCEL; that means the stepper-motor current must have NO OTHER PATH than the cable. Since there will be parasitic capacitances inside your motors, there will be currents/charges flowing through wiring-insulation to the CASE of the motor. You need to capture that current. I suggest you evaluate attaching the CASE to the cable shield, while electrically isolating the CASE; in a plastic drone, that may be simple.

EDIT Standard PCB foil is 35 microns thick (0.035 millimeters, or 1.4 mils) and weighs 1 ounce/foot^2. Frequencies at 4MHz (125 nanosecond Trise, Tfall) will be somewhat attenuated; frequencies at 16MHz (30nanosecond Trise, Tfall) should be attenuated by 2 Nepers (2 * 8.6dB); that atten of 17.2dB is not much to protect your RF Receiver front end circuits from the overloading magnetic flux of 1 amp being switched in 30 nanoseconds. PI matching circuits should be chosen to provide High Pass Filter behavior, not Low Pass Filter behavior. That means the components both before and after the PI matching are contributing to reduction of induced Magnetic field overload energy of that first RX amplifier. Thus capacitors into the PI and Out of the PI are guaranteeing High Pass Filtering; if you see a DC path from antenna to the LNA base or gate, you have failed.

One of you questions is "the open connections soldered to the board". Yes, those matter, because the distance and area from RTN to HOT wire are the loop area creating a flux that will overload the radios. Make that area as small as possible. Something like this is good:

schematic

simulate this circuit – Schematic created using CircuitLab

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Use twisted pair shielded cable. Connect each coil with respective pair conductor and connect shield to earth/ground. I would be more concerned about the EMI in your PSU that can interfere with power supply of the RF receiver/transmitter .

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  • \$\begingroup\$ Thanks for the response. I haven't had any interference with the PSU. The stepper motors are small 5V motors so the PSU is not big at all. I have definitely experiences significant interference coming from the driver to stepper wires. \$\endgroup\$ – Shawn Volpe Mar 9 '17 at 21:40
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    \$\begingroup\$ @ShawnVolpe, you need to show us how you are driving the stepper and how fast. There are ways to limit the motor noise. Best way to prevent noise problems is not to make any in the first place.... or make as little as you can. \$\endgroup\$ – Trevor_G Mar 9 '17 at 21:43
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A stepper motor and its drivers do not generate RF nor sense it. The intelligence behind the driver transistors, on the other hand, might be sensitive. A common-mode choke (one of those big ferrite bead things) with the stepper drive wiring shoved through it can be put next to the drive transistors. That keeps the motor and wiring from being an antenna.

If the cable to the stepper is loose wires (not twisted) there can be some differential pickup, so keep the wires together (or fit them into a flexible metal conduit, available at hardware stores). Ground the conduit, of course.

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