Author Topic: Raspberry Pi 3 radiated emissions test  (Read 3362 times)

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Raspberry Pi 3 radiated emissions test
« on: March 21, 2017, 07:11:20 am »

I run an open source project that is based on the Raspberry Pi.

Some of our RPi3 users report interference on VHF radio frequencies. The interference issue seems software related. The Pi3 does cause some radiated emissions issues that appear in the FCC testing report, but we believe that we're able to create further emissions depending on the software configuration (CPU clock frequency).

We don't have access to the RF equipment that I know that others may have here.
We'd like a test performed on one RPi3 in two different configurations (I'll send you two different Raspbian images). We do not need full compliance-style tests performed, just two tests that help us answer the question of whether or not we have solved an emissions problem via software configuration.

Have not had this sort of work done before, but hoping to keep the costs low - maybe less than a few hundred dollars if possible. This is a test that can be done with your own RPi3 if you have one on hand.

Offline Christopher

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Re: Raspberry Pi 3 radiated emissions test
« Reply #1 on: March 22, 2017, 06:58:53 am »
I could do conducted emissions testing, if needed.

Offline jashugan

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Re: Raspberry Pi 3 radiated emissions test
« Reply #2 on: March 30, 2017, 06:03:51 pm »
Hello, I will send a PM.

Offline AndyC_772

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Re: Raspberry Pi 3 radiated emissions test
« Reply #3 on: March 30, 2017, 06:23:26 pm »
Radiated emissions from a board the size of a Pi are generally about 10% down to the board, and 90% down to the cables connected to it. The VHF band uses and requires an antenna in the order of a metre or two long, and there's nothing on a Pi big enough to be an efficient radiator.

So, make sure that when you test the Pi in your configuration, you have a combination of PSU, enclosure (if any) and cables which closely mirror those of the customers who are reporting interference problems. Pay particular attention to whether or not any cables are shielded, and if they are, exactly where and how the shields are connected at each end.

Without replicating the cable set-up, you won't get anything which even vaguely approximates the amount of RF interference that your customers are seeing. You will see the frequencies that are being generated, but have no way to tell whether the amount of interference at those frequencies will be (a) insignificant, or (b) overwhelming.

In practical terms, the way to work around the problem might be to provide affected users with some good, accurate information about EMC, and how to modify their equipment to improve performance. A screened cable, properly grounded in the correct way, might work wonders.
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Offline wraper

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Re: Raspberry Pi 3 radiated emissions test
« Reply #4 on: March 30, 2017, 06:46:17 pm »
Sounds like crappy HDMI cables.

Offline tatus1969

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Re: Raspberry Pi 3 radiated emissions test
« Reply #5 on: March 30, 2017, 07:02:27 pm »
My guess would be a crappy power supply. The RPI's code execution modulates its current consumption, which in turn modulates radiated spectrum from the supply.
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