Over on the Hackaday YouTube channel a video by Alex Whittemore has been uploaded showing how to do some basic RF emissions debugging. When creating electronic products it's important to ensure that there is no unintentional RF leakage in excess of emissions standards, and there is often a need to debug a circuit board to determine exactly what part or areas are generating excessive RF noise. To do this expensive EMC analyzers and near field probes are typically used.
Alex's tutorial video shows us how we can create a low cost home made EMC probe using an RTL-SDR, LNA and home made near field probe made out of magnet wire. The video starts by explaining RF compliance, demonstrating some higher end equipment, then moves on to showing how to build a probe yourself, before finally demonstrating it being used on some circuit boards. For software, he uses SDRAngel and QSPectrumAnalzyer which are preinstalled on a DragonOS image.
The Hacakday.io project page has the tutorial in text and the video slides can be found here.
In the past we've also seen another post about home made EMC probes, and how to combine this idea with OpenCV to create noise heatmaps of circuit boards.
Basics of RF Emissions Debugging: Alex Whittemore
Over on YouTube and his blog user Charles Grassin has uploaded a short video and blog post showing how he's using an RTL-SDR EMI (electromagnetic interference) probe and OpenCV to create a visual EMI heatmap.
Earlier this month we posted about Dmitris' experiments in which he was able to create a home made EMI/EMC probe out of a loop of semi-rigid coax and an RTL-SDR V3. This type of probe is useful for determining what components or areas on a circuit board are emitting electromagnetic interference. EMI testing for PCBs may be critical for passing compliance tests.
Charles' project takes the RTL-SDR EMI probe idea a step further by combining it with OpenCV. OpenCV is an open source library of code for computer vision applications. With the EMI data generated by the RTL-SDR EMI probe, and a camera pointed at a PCB, Charles is able to overlay a heatmap on top of the visual image which reveals the EMI hot spots on a PCB.
The video below shows the EMI heatmap of an Arduino PCB being mapped out. His blog post shows some other examples like a keyboard and a hairpin RF filter. The code he's created is open source and available on his EMI_Mapper GitHub page.
EMI mapping (OpenCV and RTL-SDR)
Luis Colunga has posted an interesting tip on his blog on how he reduced broadcast FM interference in the rtl-sdr dongle. He writes
Many people have noticed that even if there is not an antenna connected to the RTL SDR FM Stations still come strong. This is not good at all because these are signals that are getting into the PCB via another way that is not the antenna.
He then goes on to explain a method he used to significantly reduce the interference, which involves removing the male USB connector from the dongle PCB, and fitting your own USB cable leaving the shield floating, which he then wraps with aluminium foil.
Check out the rest of his post here.