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Topic: EMI issue from Arduino (Read 1 time) previous topic - next topic


I have an Arduino Uno that I have running that's fading a color RGB.  I noticed that when it's running my scanner picks up stray signals at times in the 70 cm band. Any suggestions on how to eliminate/reduce the interference?  I've also experienced the issue with even the blink example running.

James C4S

Put the Arduino in a box.

What frequency range is that?
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com


It's in the 420-450 MHz range.


I also experience the issue on my Mega 2650 (sainsmart clone).


Yes any digital processor will radiate. While the arduino is only 16MHz it is the harmonics in the edges of these signals go right up. The same goes for PWM. You can try putting a very small cap of about 100pF to take the edge off the PWM signal.
de G8HBR


Feb 04, 2013, 08:55 pm Last Edit: Feb 04, 2013, 09:01 pm by Nicknml Reason: 1
Thanks for the suggestion, will get some of those caps. Stupid question, should those caps be placed in parallel or in series?


Feb 04, 2013, 08:58 pm Last Edit: Feb 04, 2013, 09:08 pm by pito Reason: 1
An MCU is always a pain when combined with receivers circuits, as it generates a broad range of spectra, from zero to GHz.. The best way to learn how to tackle that is to download a service manual of a receiver or transceiver (ie. Icom, Yeasu, Kenwood) and simply have a look at the schematics.

Usually the main clock frequency is chosen such it does not fit into any filters, and, it does not mix with other oscillators used. Mind a traditional scanner might have 3-5mixers and several IF stages. So you have to tune the mcu main clock thus any spurious mixing products (all sums and differences of all frequencies with all their harmonics) inside the radio will not fit into any filter and in any band/channel used. That is very difficult.

Of course any digital signal with sharp edges generates a broad spectra by default, so low-pass filtering of any signal coming from the MCU is a must, where applicable.. And good shielding, grounding and decoupling helps as well.


Thanks for the suggestion, will get some of those caps. Stupid question, should those caps be placed in parallel or in series?

In parallel, across the LEDs

You are better off trying to remove the source of the interference that trying to modify the receiver.

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