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- Опубліковано 20 сер 2024
- How to make your own magnetic H-field EMC probe out of semi-rigid coax for $10 that performs identically to a $300 commercial probe!
Search for "Low noise amplifier" and "semi-rigid rg402" on ebay.
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Now build a additional spectrum analyzer for 10 bucks and every one is happy ;-)
Would a SDR make a decent spectrum analyzer? I guess most have a more limited range though.
It would definitely work, although you'd have to be careful about the input signal level as they saturate easily, it also takes a good amount of time to sweep a large bandwidth.
Yes a HackRF would have more than enough frequency range although slow sweep (but then do we care?). They are a bit 'deaf' though. Can't hurt to try though can it?
Test it with RTLSDR for 10$
Dave should probably do a video with $165 handheld spectrum Analysers from rfexplorer.com
One of the best videos in a while!
@qashqai q Spot on. I'd rather have Dave post rarer, but higher effort content.
I don't watch the mailbags anymore, they seem to become a chore for him. Teardowns are a hit or miss really. Dave sometimes does too little research. Though that correlates with "off-the-cuff" slogan.
RicoElectrico Correct, I do practically zero research, that's the way I've always done videos and have built my channel from nothing doing that.
@@EEVblog How about more DIY expensive tools that work as well as the professional ones. Stickin' it to the man. How about an active oscilloscope probe next? Or a DIY Hewlett Packard 547a current tracer? I could probably use one but not enough to justify $200 on ebay
Totally agree .. high quality content .. stick it to the fat cats Dave .. maybe build a differential probe next from Ebay parts .. there are a ton of broke engineers and hobbyists out there
Yes sir. An RF probe came to mind from an old set of computer external speakers... that'd be about as cost effective. SDR ideas don't seem bad for cheap spectrum analyzers especially if there is an oscilloscope plugin... though I've figured a set of attenuators for the range and profiling the SDR well to know its range of performance to characterize the limitations so you don't blow it up. Probably a current limiting input thingamajiggy too. Normalizer dohicky would be impressive. Least that's what comes to mind. I was also wondering about making a leveling head for the cheapo signal generators since they're so cost effective. Trips me out how cheap some of the modules are and how like this detailed video demonstrates using the hardline or rigid or I guess it's called semi-rigid cable... can be used to make decent kit alone basically or with a or some modules. So much, I just ordered a range of modules, plus some, to make an Antenna Analyzer or looks like is going to be a VNA using Erik's latest modularized version he notes on the SoftwareControlledHamRadio groups.io post on Analyzer Comparison since seems impressive: github.com/erikkaashoek/Tapr-VNA
Another solution for your rubber coating: buy ABS filament for 3d printers and solve it in acetone. Then you can use a brush to apply it. The acetone vaporizes on its own at >20°C and only the ABS is left
That faint thudding at the end of the video is Tekbox executives jumping out of the windows.
I'm looking forward to next video "Build a $100 DIY Spectrum Analyzer"
It might not be $10, but the W7ZOI homebrew SA was a good design/project from the '90's, rebooted here:
hfsignals.blogspot.com/p/specan-reboot-of-w7zoi.html
I have done that (500 MHz) , is a lot of work, by the time it was finished I had a few real SA's. www.pa4tim.nl/?p=1643 , it is a while back so the page is in Dutch, newer projects etc are in English.
You had time to build it to scale and to paint it!!!
Only two coats!
@@EEVblog I believe this would do a better job coating it than the spray-can version: www.amazon.com/Performix-11602-6-075815116024-Plasti-Dip/dp/B000ZN1T16/ref=sr_1_9?keywords=plastidip&qid=1549645102&sr=8-9
@@altersami9660 yeah... I saw the name Plasti-DIP ... and a spray can, and I was like... what? Plasti-Dip is supposed to be a thing you *_DIP_* into, not spray on.... silly people, giving them a market for this.... (I mean, I suppose there are probably use cases where dipping is impossible and the spray is useful. But for this use case? Dipping seems entirely appropriate. Ah well.)
I came here to say this is one of your best videos in a while and am amazed to see how many others are saying the same thing. I couldn't believe you peeled back that Tekbox cover; thanks for doing that!
It's funny that I don't have any use for the probe but found it so entertaining.
For all those wondering the weird round package is a type 86 plastic package, and the amplifier, which has only GND, IN, OUT, is a MSA0486.
Need more of these typ of videos
I may actually join the discussion over on the forum. We have billions of these DIY H-field probes in our lab of varying qualities. Might be rather entertaining to post a picture of all of them.
Please do!
You don't need plasti-dip for probe coating, use electrical tape. It almost looks like the cheaper one could be prototyped in strip board if the need was urgent enough. For a cheap spectrum analyzer, attach a 10 MSPS SPI ADC to a raspberry pi, write some code to perform FFT on the data using the GPU and pipe the output to a graphing utility to get an approximation of a spectrum analyzer.
Not sure why you have a few thumbs down. A huge money saver that will give the same performance. This is great Dave. Thank you yet again
The thumbs down will be from the company that makes the probes or from people who bought the probes and now feel like they wasted their money.
I got loads of those RF amps sitting around, they're handy because you can use a buck converter and set the output voltage to calibrate gain with them, no need to use an attenuator.
That coax looks like they just dipped normal braided shielding and dipped it in some solder.
That is exactly what they did.
Thats how many places make semi-rigid in the smaller coax styles. Very common.
Welcome to the world of radio frequency hobbyists / radio amateurs!
We knew this all the time. I made such a probe years ago and used it many times, it is also useful to tap off some signal from an oscillator coil to measure the frequency using a counter, to tune a transmitter amplifier while constructing/experimenting, etc etc.
Yes, they are quite common.
Is it also usefull for making measurements in Audio circuits? I'm thinking off finding noise sources in the 1khz to 40khz range.
Afaik RF is much higher then what interferes with audio ...
For that I have a different probe that has a coil with some more turns at the end.
Just a length of RG58 with a BNC at one end (for the scope) and a coil made from .5mm enamelled wire that I threaded through a length of insulation tube (4-5cm), ends pulled together so it forms a small loop.
Finished with some heatshrink to cover the solder joint to the end of the cable.
Experiment with the number of turns depending on the signal pickup level you need and the high-frequency response. For this region it should not be a problem to have like 20-40 turns, but of course it will no longer work so well in the MHz range.
We knew this all the time, I made one years ago. Well why didn’t you take the time and effort and put it up on UA-cam and not wait for other people. With your sort of attitude no wonder the young people are not coming into amateur electronics. Why are your sort so protective of knowledge?
@@KidCe. Just use a normal flat coil for that and either a cheap oscilloscope or a cheap audio amplifier. Or search for "superprobe".
Use the PastiDip in the non-aerosol can or liquid electrical tape and you will be much happier.
Also, you can make the very small loops from very small diameter coax. The coax does not need to be rigid, and if you put some steel wires or small fiberglass/carbon-fiber rods along side the coax for the small loop, it will add the needed rigidity. Use heat shrink over the coax and stiffener for the straight part and dip/paint on the liquid tape over the loop.
The small loop can be even more finicky to cut and solder, so short the end of it back over the coax before bending it into the loop, then solder the whole end back to the shield to make the loop. To cut the gap in the middle, you only need to make a single slice, and when you dip it or brush on the tape, it will fill that slot and Robert is your mother’s brother.
You know you need to take this to the next level right?
First you use a 3d printer as x/y scanning platform for the board (printer can be fed gcode for movements from pc via usb) and then record the data from the oscilloscope via for example python integration with scope (usb again). Recording the spectrum on each position in a grid and display everything in a nice overlay on a photo of the board. User could then either see a sum/max of all the emissions or scroll through the spectrum and visualize a frequency slice in the overlay. Now that's sexy!
Yes, I said that in the previous video.
There is a product out there that is an array of loops in a paper sheet size bed. Its multiplexed and scanned into an analyser. You can put an image of the pcb layout over the scan data to give you an RF 'heat' image. Think its made by Emscan.com from memory.
@@simonbaxter8001 I know. I've used one. This is cheaper and more fun...
Good noise floor for the couple dollar pre-amp.
I've seen worse from decent commercial jobs.
You can also make a quick and dirty e-field probe by cutting away some shield leaving a very short stub of the solid core conductor then insulating against shorts.
Even if you don't have a specan these tools are useful with an oscilloscope (you will need the preamp). If it has fft like most dso do then that is a bonus.
Home made H-felds are great, beat the old emco kit any day of the week
we've always called that soldered braid stuff "semi-rigid" coax. Solid copper outer shield was called "rigid" ..
Yes, it's semi-rigid.
Actually the right term for this stuff is "handflex." Examples of semi-rigid coax would include the 0.086" and 0.141" cables with the solid tinned-copper shield that you see in commercial spectrum analyzers and other RF gear. It is not meant to be formed by hand and often breaks when you try.
We always made our own probes like this. You can make them more selectable by adjusting the size of the loop.
I built an EMC probe for less than $8, using a toraial core coil and soic op amp. I needed to measure current WITHOUT physically touching the current-carrying conductor. Torrid core coil to the rescue! You can see it, and the printed circuit board CAD files that I offer as "open source", on my MeWe page @ Esp and IoT
Great, now I just need a Spectrum analyzer :|
You scope likely has FFT
@@EEVblog or cheap RTL dongle or HackRf will work.
As SpecA’s go, you can likely get the Rigel jobbie that Dave was using for ~1500 $USD or less. That’s serious coin, but WAY cheaper than an equivalent unit a decade ago...
Yeah about $20 for the RTL SDR + Spektrum (free)
www.rtl-sdr.com/poor-mans-spectrum-analyzer-with-an-rtl-sdr-and-noise-source/
@@samuelcomeau Install it with Pothosware. Dead easy.
That piece of coax is beautiful.
I think you might be slightly wrong about the commercial probe coating. I feel like they did a grippy gritty transparent conformal coating to help adhesion of the blue shmoo.
Possibly
The guys at tekbox spent houndres of hours on r&d for this thing to work properly.
Dave botches something together in 10 minutes and it works just as fine if not better than the pro kit. :D
R&D, or D&M (design & marketing)? :P
Research & Development
Getting those curves that are individual, and that are a true reflection on the device, as opposed to lucky try and it worked. Plus the whole repeatable manufacture thing that means you can interchange probes, and not have to run a calibration on each new one you get, just use the curve supplied, which is well within a specified tolerance spread.
That's the kinds of videos we are here for. Thank you!
13:29 It looks like a tool handle dip to me 4:14 the surface finish is rough, bumpy, and full of holes.
It's likely the same thing you used Plastidip and that shade of blue is one of the three shades they sell. It also comes in a can so you can dunk the part rather than spray it.
Just just dunk the PCB into the container, pull it out, and let it drip dry. Repeat the process to thicken the coat.
Bushougoma Looks like they also used some primer coating to make rough surface layer on PCB and make it stick.
Well, that came in handy! Things ordered, now the waiting begins. Thanks a lot!
Looking forward to the E-field probe.
Great video Dave! The blue coating on the outside of the TekBox probes is likely a low-pressure overmold, which is the same material used on strain reliefs for cables, etc.
love all your videos, but i have a preference on EMC/EMI things, keep it up
You can make the H-field loop solder connection and shield cutting in many ways. There will be very little performance difference if you make it unsymmetric and just solder the center conductor to the shield on one side. Yeah, it won't be geometrically symmetric, but it will be electrically almost the same as the more complicated construction.
Nice video, one has to question why the commercial one’s are so expensive. It reminds me of when companies rub off chip numbers to hide how they are made. Probably also would reveal the company’s mark up vs actual part costs
Very instructive - thank you!
Great video! This is the kind of content that I really like, this is definitely worth the patreon subscription.
Thanks again Dave. Way cheaper and super easy. You’re the man!!! Gonna build my own.
In my book, this is a proper tear down.
Great work.
Dave's videos are really fun to watch. Few other channels can do the same.
Great video as always, Dave. We’re dealing with an EMC issue on a project right now..
them cheap amps are perfect to use for RTL-SDRs aswell..infact you can use this probe on a SDR and find the same results!
Yes, they advertise them for that
Now start mass production and sell it on Ebay for $50 and bundle it with calibration certificate "Calibrated by Dave".
A cal cert on a post-it note...
Brilliant dialogue, very entertaining and informative. Many thanks for sharing
Awesome video, I like how you show that doing EMI measurements is easy. And in my electronics courses they said I'd never do that unless I go to university, yeah... Right.
Great Video. Top marks for peeling back the rubber.
Great video! Waiting for Part 2 with a little EMI pre-testing howto!
excellent video. I hope you make the follow up videos as you mentioned. I would also love to see a differential version of this instead of single ended. I think high end EMC probes must be differential to suppress common mode noise and enhance sensitivity. In the end it can be converted to single ended using a balun or something.
Someone asked if this can be used in audio frequencies, I think the voltage induced in that loop must be proportional to frequency as well as the loop area, so at audio frequency, the picked up voltage will be way below noise level
Excellent! Thank you Dave. Videos like this are why I subscribe to EEVblog.
I love RG402. Nothing better for DIY antennas
That was ace, enjoyed that. I was thinking u could 3D print a mould for the coating.
When I play our video at 2x speed you become an electronic squeaky madman!
Play it backward... Dave is dead...
Thanks, Dave! Very good.
As someone else said on the comments, I'd like to see how an oscilloscope FFT using this probe compares to the spectrum analyzer, for the ultimate thrifty EMI measurements!
Great idea! I just happen to have a box of surplus semi-rigid SMA jumpers (and some with 1 end off,) and 3 or 4 of those little amps, AND some ferrite cable clams, but no EMC probe! I'll do it!
BTW, that is braid on the coax cables, but it is saturated with something much like solder, ensuring 100% coverage.
Frigging amazing hack! Everyone is going to build one. Thank you Dave, really
Great video Dave! Could you do a similar frequency domain analysis with an oscilloscope's FFT? Just to make it a lot cheaper and accesible, since it's a more common tool.
I would love a video on using FFT function to make these measurements. I think building one of these probes would be a lot of fun for $10. A spectrum analyzer is out of the question for me, and probably a lot of hobbyist, but I do got a scope with FFT.
You could potentially use fft on a scope, if you had a scope with 1+Ghz bandwith. A new 1Ghz scope is in the $10k vicinity. A hacked to 3.2Ghz Siglent spectrum analyzer is about $1700. A HackRF SDR is about $250, and I believe with the correct firmware sweeps 6Ghz rapidly. The lower cost devices would not be calibrated or have features like like tracking generator, so the hacked spectrum analyzer has some significant attractions. There are also PC based vector network analyzers, which add a lot of additional functionality, as they measure phase shift in addition to amplitude. A full duplex SDR + a ebay reflection bridge might be a usable vna with the right software.
Love the enthusiasm. How about doing the E field probe next ?
Great video. In the pre-compliance process right now for an IVD device with the cheapest company on the planet.. I seriously hope it doesn't come down to me building one of these. Thanks.
39 dislikes are from EMC probe manufacturers lol
Excellent idea!
You can buy the cans of plasti dip, probably works better than the spray. Also, using a spray paint primer first might help it stick better.
Great video and the answer to my needs for a cheaper and accurate way to measure fields. I enjoyed the 2 layer/four layer computer boards comparison you did recently but shuddered at the $300.00 Tek probe kit price. I used to make sniffer probes for use in troubleshooting radio xmtrs and receivers which were of course uncalibrated. I consider what you taught us to do here to be close to calibrated. Thanks for the unselfishness.
Should be pretty close to the performance of the professional Tekbox one. I can do some more detailed measurements and comparison, but it's looks as close as you can get. Although with near field probes you aren't really dealing with absolute quantitative measurements.
Dave, thank you and here is a project request: Would you design, build and test the efficiency of a
a Joule Thief circuit. There have been many offerings but I have never see any commercial products. I recall you commented in the past about the LED in a similar circuit not having a current limiting resistor. Some of the offerings have run a long time on a battery. I have designed my own 1.5VDC non Joule Thief LED "flyback circuit that generates a sine wave that I thought might recharge the battery but did not even though LTSpice indicated that it might. I also have a LTSpice design that uses very little 1.5VDC battery current to drive a LED but I can't get it to run in the real world. Still trying........
Good job Dave!
Cat nail scissors are excellent for stripping braid off small coaxes.
I love this kind of videos comparations. More videos like that, please. Expensive VS Cheap. Who is gonna win?
Usually there is a performance difference, but in this case pretty identical!
@@EEVblog EEVblog I agree. But for a simple mortal like me and others learners, $10 to $300 makes a lot of difference.
Dave, you need an x-ray machine. Just saying :-)
Not possible to buy one here without a license.
@@EEVblog ugh. That sucks.
I like the type of x-ray machine bigclive uses ;)
@@zvpunry1971 Bigclive has an x-ray machine ?
Hahaha I have a lot of different x-ray models at home and didn't know it.... Hilarious
A good appropriate spray paint should do the same job nicely as the plastic dip here.
This Dave! This is why we subscribe. Now, can you show how to build a DSA 815 for those of us that can't afford one? Haha
Excellent video. This was quite interesting and useful. Please do the video in compliance.
Just another grand Video!
Very educative and interesting!
Keep it up! Good onya Dave :)
I just missed a DaveCad with EM fields around the probe, so we can understand better how the fields convert to Volts into the probe, for the signal analyser
Oh, nice. I saw the other EMC video and was thinking about 3d printing something and winding the head with the various reels of magnet wire I have here. I also have lots of rigid coax so winner, winner chicken dinner.
The clue is in the name; PlastiDIP. Always better dipped if possible rather than sprayed. Mix and let settle to allow bubbles to come out before dipping. Keep moving while drying for even coating. Buy Pastidip thinners (naphtha) at same time in order to vary thickness (let evaporate to thicken, add thinners to thin). Store in fully sealed container otherwise it will be solid when you come back to it in a few months time.
Those tiny amplifiers are the MAR series from minicircuits.com. They have been around since the late 1970's. This is the MAR-2 line.
www.minicircuits.com/WebStore/dashboard.html?model=MAR-2SM%2B
I'm sure it would be possible to build a $50 active probe that performs close to a $5000 keysight active probe. But the problem is, in order to do that, you need a very expensive spectrum analyzer and all related RF electronics gear. And once you have invested $100,000 dollars for all that gear, you wouldn't want to sell the product with just say a 100% margin, cause if you do, it would take decades to amortize your investment.
Awesome! Never knew there was just a trace and a plane to it
Nice little project that one. Thanks for an great video.
While the $10 option is VERY useful, the $300 kit has all sorts of calibration graphs and "reproducibility" when you get it. It might not be necessary in ALL instances, but if you are doing a nice funded project that HAS to meet specifications, you may need the $300 option. For me the $10 option will get me there for over 99% of the time.
The thing with near-field measurements is that you are not doing quantitative absolute measurements, so the point is a bit moot for most cases.
But wouldn't you use an anechoic RF test chamber for calibrated EMC tests?
Would the 300 dollar calibrated probe be the measurement antenna?
I NEVER found using this type of probe to find where the RE noise was coming from. The noise was everywhere, every component, every power rail. So trying to fix an RE compliance issue was not done with this sort of test gear.
We joked that what we needed was eye sight that could see the circuit board in the frequency of interest to find the component and power connections radiating.
What I did learn was how to design proper decoupling to each component, and paying special attention to components that drove wide processor bus (octal, 16) paths, as these are charging the circuit traces which is what causes the RE problem in the first place. Our PC design department was useless, as they would just place the decoupling components around the board. We figured out how to source the power for each IC on the PWB, so they were not directly connected to the power planes, but instead to multiple capacitors, which then had power connected to Vcc and such. The inductance of these traces had to be kept minimal. The idea is that the decoupling provided the high frequency currents for charging the board capacitance/inductance. It was tough, as we dealt with non technical board designers, that wanted to turn the autorouter on.
It takes a smaller loop - which will provide higher spatial resolution. 2 turns of 32awg (or so) enameled wire on 2-3mm dia (wire wrap wire also works), 50-ohm resistor in series and coax. Preamp required. Works well.
@@milantrcka121 I never found any ability to find the source of the emission as any quantitative measurements were "noise here, and more noise there". The circuit boards were 150mm X 250mm. In 1988 the processor frequencies were 6-10MHz, but this morphed to 32MHz, to 128Mhz. The lab had multiple HP brand probes. When I was still green starting out, the technicians just laughed, as they knew the root cause of the emission was not found by this method. The RE plot would show which processor frequencies were the source of emission limit exceeded. So we would try to bandaid the boards with capacitors and such.
In the end, these original designs were ultra crap, and the fix was a new board layout. My job was to integrate a card cage of 19 microprocessors and make it pass the environmental requirements. This was avionics, the test methods were from RTCA DO-160 (version G when I retired). There were very deep notches to the RE bode plot at the comm radios, and nav radio frequencies. And super position of the emissions from these processors was a challenge.
Well if the emissions are everywhere, then the design has a major problem as described. Been there, fixed that.
Seems to me that Tekbox is not at all pleased with this video :-)
Would be cool to create a heat map showing how much is radiated as a function of the probe position. What would be the best way to realize that?
I have several idea, from modding a 3D printer, to a line scanner, to a full array scanner.
EEVblog Would be especially cool to create a volumetric scan for discerning between near and far field. But anyway, just saying. :)
Well done
I die a little on the inside every time Dave does anything RF related. Just a little.
That's pretty ridiculous. Cool video Dave!
Was hoping you might go into this a bit deeper. Thanks!
In what way?
EEVblog not the poster but I loved the video but I would also love, maybe in a follow-up, how/why the probe is designed that way, why the symmetry and impedance matching are so important.
In any case, I'm loving the EMI/EMC series!
@@EEVblog I'd guess he meant it as "after watching the previous video, I was hoping you would dig deeper. Thanks for doing it! “ as that's what I feel too. And please keep them coming! :)
Please do a Rogowski Current Probe next!
*semi-rigid. You can't bend rigid coax without destroying it
Yeah, correct.
@@EEVblog This cable is actually called "conformable" coax cable. Meant to be shaped for final application, but not for repeated flexing/bending. Good video. Thanks!
Yes you can. Like a plumber. Just not by hand.
Martin Krehl Yeah you could even bend it by hand if you're careful and keep your bend radius large enough. You could use a 10mm pipe/rod/drillbit shaft and bend it around there for example.. Depends on how big it is obviously, you're not gonna bend the 50mm (or so) stuff at the TV station
Rigid coax often use air dielectric. If you bend them, you will change the impedance and risk the inner conductor touching the outer conductor.
There are specific L-pieces for rigid coax, but often they are custom made anyway (soldered/welded). Rigid is really not meant to be bent.
Dave has a nice video from a TV transmitter site where they had rigid coax pipes.
You can use a 1 gallon of bed liner and dip it
Excellent video, more diy stuff. The difference in price is shocking, electrons spontaneously felt off if they had any notice of value.
Thank You .
I built one too. Works fine!
Dave thank you for this video really useful video so many applications, looking forward to an official diy PCB.
Why not get in touch with an institute or university to test it?
Our RF professor would certainly be interested in testing such a thing, even just for the lols.
Oh shit! Just when I thought I am going to make a killing with my $300 probe set, Dave got one under $100
Steve Irwin of the electronic jungle.
You could characterize the two amps for frequency response, that might be the only tech difference.?
There are some cheep pcb emc probes on aliexpress, maybe test those? Just search for EMC EMI Probe. 50$ for a set of 3 h -field and 1-e field.
So I can use this to get the signal from the speaker wire on my Panasonic SA-PM46 Self Stereo (which I purchased from JB-HI-FI Woden in Canberra in 2007/08) amplify it so I can use it as line in for my TDK S60 Tremor Subwoofer!
Very useful. Thank you.!!!
Plasti Dip recommends a primer coating first, I don't know if it has to be there's or if any primer will do.
@EEVblog can you do a tutorial with using an SDR and an EMC probe?