waveguide near field probe vs loop probe - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: August 28, 2017, 02:12:18 am
content: I see some manufacturers sell waveguide to coaxial adapters to function as a NF probe.What are the merits to doing this vs using a coaxial loop?

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: August 28, 2017, 09:59:00 pm
content: Could you provide an example?

author: CopperCone
author_rank: Super Contributor
timestamp: August 29, 2017, 05:23:34 am
content: https://www.nsi-mi.com/products/antenna-products/waveguide-probeslooks like a waveguide with some rf blocking stuff around it

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: August 29, 2017, 10:22:15 pm
content: Ok, they are intended for a totally different application. The near field of antennas (see Fresnel zone -> several wavelengths) is far larger than the distance and spatial resolution involved in EMC troubleshooting. I don't think that those products are applicable to this area. But interesting..

author: CopperCone
author_rank: Super Contributor
timestamp: August 29, 2017, 10:53:04 pm
content: well i mean if your in an installation and trying to find out whats radiating, they seem like the right tool for the job, just walk around next to diff boxes and point the waveguide at them, or for bug searchingI don't see why it would matter the wavelenght so long the waveguide is the right size, right? especially for stuff <1ghz. I don't see how the hell I am going to be walking around with a TV antenna or something.. or be able to afford something like a rhode swhortz antenaLoop probe does not seem like the right tool for the job but idk

author: tautech
author_rank: Super Contributor
timestamp: August 29, 2017, 11:05:44 pm
content: Quote from: CopperCone on August 29, 2017, 10:53:04 pmIf you're serious about this member Fraser found these a few months back:https://www.eevblog.com/forum/testgear/new-affordable-emc-probe-set-at-a-bargain-price-from-ariel-rocholl's-lab/

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: August 29, 2017, 11:20:56 pm
content: I would say that you are correct. The question came across as coming from the side of typical loop probe applications.For what you have in mind give them a try.

author: CopperCone
author_rank: Super Contributor
timestamp: August 30, 2017, 03:41:58 am
content: Quote from: tautech on August 29, 2017, 11:05:44 pmI made a bunch of my own loop probes

author: tautech
author_rank: Super Contributor
timestamp: August 30, 2017, 04:14:07 am
content: Quote from: CopperCone on August 30, 2017, 03:41:58 amAnd they might work fine but will they have the directivity of commercially made sniffer probes ?In some applications you might need fine resolution (SMD) to determine where exactly emissions are originating.Just my 2c.

author: CopperCone
author_rank: Super Contributor
timestamp: August 30, 2017, 06:19:42 am
content: Ah, I am more interested in environmental use and measurements, not so much on PCB/chassis inspection level.Would be nice if someone provided blueprints for that thing.. hint hint.. *cough*

author: DaJMasta
author_rank: Super Contributor
timestamp: August 30, 2017, 06:46:11 am
content: After looking at the little blurb about it, maybe that's the reason for the difference: these are minimally invasive for near field applications. Normal near field stuff operates close enough to effect the system being probed and as such it couples into it, but something like this would give you a very narrow, high sensitivity antenna that will work at a distance so as not to interfere as much as a standard probe, but still give you the detailed feedback you get from normal probes in close proximity.While they'd probably work fine as very directional antennae, why not just look for a normal horn or other directional antenna for environmental measurements? If you want omnidirectional, there's a whole slew of E field probes around.

author: CopperCone
author_rank: Super Contributor
timestamp: August 30, 2017, 09:57:35 am
content: a horn that goes down to 200 MHz is not available, it costs like 5g. I have horns that can do it (but not in their spec), but I would prefer something inherantly narrow band so you don't get possibly confused by IMD, mixing, gain compression. Always better to have a filter, and the least invasive type of filter is the antenna itself.And, its light, and cheap, if you make it out of thin sheet metal.And you can make alot of them and network it to a switching box if you wanna monitor a buncha stuff at the same time. Doing that with regular equipment will drain the bank real fast vs some thing made of sheet metal, a N connector and some metal rod.I feel like it blows all the options out of the water because of cost, so long you manufacuter it yourself and solder or braze them yourself. Or even rivets for the lower frequencies.I guess you can make your own horns, but its alot more work,, this consists of 1 piece of sheet metal cut out like a box shape, or 2 pieces if you want to save materialI guess making standard gain horns is an option.. but still for like 400MHz its alot smaller just to have the waveguide section.. if you flare it out its going to be truely massive.

author: tautech
author_rank: Super Contributor
timestamp: August 30, 2017, 10:01:29 am
content: Quote from: CopperCone on August 30, 2017, 09:57:35 am200 milli Hertz is very low. You didn't mean Megahertz did you ?

author: CopperCone
author_rank: Super Contributor
timestamp: August 30, 2017, 10:02:36 am
content: Quote from: tautech on August 30, 2017, 10:01:29 amuntil I have some von numan machines to turn the moon into an antenna, yes.

author: tautech
author_rank: Super Contributor
timestamp: August 30, 2017, 10:07:51 am
content: Quote from: CopperCone on August 30, 2017, 10:02:36 amPlease use the correct unit abbreviations, this is an engineering forum.

author: DaJMasta
author_rank: Super Contributor
timestamp: August 30, 2017, 04:29:32 pm
content: If I was more of an RF and metal work guy, making a horn out of a school bus would be a fun project, don't think it could make it down to a Hertz, though, we'd have to go bigger.

author: CopperCone
author_rank: Super Contributor
timestamp: August 31, 2017, 06:14:22 pm
content: lol, for some reason I thought of the old kids show with the magic school bus that went to mars and stuff