Build your own EMC Probes  - Page 1
Forum section: electronics / projects

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 28, 2020, 01:34:03 pm
content: Hi,EMC probes are useful for locating sources of EMC on PCBs. They are available at a moderate cost fromBeehive Electronicshttps://beehive-electronics.com/probes.htmlandTekboxhttps://www.tekbox.com/product/tekbox-tbps01-emc-near-field-probes/Dave made a series of videos on using these probes and making your own H-field probe:In EEVBlog 1178 Dave constructs an H-Field probe using semi-rigid coax and coating in Plasti Dip.H-Field ProbesThese are simply single turn coils that used to detect varying magnetic fields. They are shielded from the E-Field using coaxial construction.E-Field ProbesThese are simply a short conductor that is capacitively coupled to the noise source.3-D Printed constructionI decided to use a 3-D printed construction to provide the mechanical support and insulation.The probes are constructed from three parts:The body of the probe, two pieces, is made from PLA.The strain relief for the coax is made from TPU.All the electrical connections where made with RG316 coax.PhotographRegards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 28, 2020, 01:51:01 pm
content: Hi,Here are some of the detailsFusion 360 DesignH-ProbeE-ProbeConstructionThis shows how the coil is constructed.SMA Strain ReliefA matching strain relief was made for the SMA connector using TPU filament.The E-Field probe is constructed by removing the outer jacket and braid shield from the 12mm at the end of the cable and gluing the cable in the probe body.Regards,Jay_Diddy_B

author: David Hess
author_rank: Super Contributor
timestamp: June 28, 2020, 09:37:37 pm
content: Appendix J of Linear Technology application note 70 shows the design of a magnetic EMI sniffer probe which can be used for much more precise applications:https://www.analog.com/media/en/technical-documentation/application-notes/an70.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 28, 2020, 09:48:56 pm
content: Here's a lower profile one, though lacking shielding:Two turns #24 hookup wire, soldered to a length of RG-174. I forget if I put a termination resistor on it or not... (Huh, just checking, it measure 26 ohms at the connector end. Now Ireallydon't know what I did...)The effect of no shielding, is some E-field sensitivity. This can be somewhat inconvenient in practice, but when understood, can also be kind of useful.It could also be made with a balun, turning the balanced loop into coax. This would perform about as well as the coax loop type above.I've also tried the slotted cylinder shield; it has lower sensitivity, and an off-center axis (because the slot acts like an angled end). The coil inside is still a dipole, you literally just can't put anything on the other end of it, mechanically or electrically. I don't think this is all that helpful. I prefer the open loop style.Tim

author: floobydust
author_rank: Super Contributor
timestamp: June 28, 2020, 11:57:32 pm
content: Bozo engineer broke aRohde & Schwarz near-field EMI probethey are excellent, compact, flat response and work quite well. But did not purchase probe "extended warranty"and they wanted over $800 for a replacement... so I took it apart and was surprised to seethe wand is actually a ball point pen, nicely dip-coated and the connector just fits in the end.The Beehive ones I find inexpensive and big and clunky. With compact PCB designs you can't get a fat probe near things.