DIY DM /CM Seperator for EMC - LISN Mate - Page 1
Forum section: electronics / projects

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 03, 2020, 09:55:18 am
content: Hi Group,I am going to share the analysis and design of device to separate Differential Mode, DM, and Common Mode, CM, conducted emissions from two LISNs.If you Google this subject this device is often called a 'LISN Mate' I believe the term was invented by M.J. Nave.These devices are available commercially, one device is the Tekbox TBLM1.Not all of the information on the internet and the designs of some of the commercial designs are correct.After I have analyzed some of the solutions that can be found on the web, I will present the design and construction of a device that works properly.We will start with an analysis of the issue, so that we understand the requirements.AnalysisI am going to start with the analysis of the LISN.The name LISN, stands for Line Impedance Stabilization Network. It presents a defined impedance to the device under test.Common LISNs are 5uH and 50uH.The impedance is defined by the parallel combination of the inductor and the resistor.LISN ModelThis model can be used to measure the impedance of the LISN.This is the impedance it is 50decreasing at low frequencies.2 LISNs and CM and DM ImpedancesTwo LISNs are used in most EMC measurements to capture CM and DM emissions.DM ImpedanceWhen two LISNs are used:The result is:It should not be a surprise, but the impedance for DM signals is 100CM ImpedanceSimilarly for CM:The resulting impedance:The answer 25should not be a surprise.Target SpecificationWhen the LISN Mate is introduced to separate DM and CM emissions these Impedances should not change.The DM impedance should be 100The CM impedance should be 25To be continued …Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 03, 2020, 10:37:44 am
content: Hi group,Mark Nave presents his LISN Mate design in this Video:The circuit is:This is often implemented like this:To be continued …Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 03, 2020, 10:49:12 am
content: Hi Group,I will continue with an analysis of Mark Nave's circuit.CM ImpedanceModelModeling ResultsThe results show that the CM impedance is 25This is the correct valueDM ImpedanceModelModeling ResultThe modeling result show that the DM impedance is 25The circuit is flawedThe desired DM impedance, as explained earlier in the thread, is 100\$\Omega\$To be continued …Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 03, 2020, 11:54:02 am
content: Hi group,I will continue by looking at the circuit proposed by Sanjaya Maniktala in this EDN article:https://www.edn.com/measurements-and-limits-of-conducted-emi/In this design the transformer is specified as 2:1. Most power supply designers would think of the turns ratio being 2:1.RF engineers would think of this a being the impedance ratio of 2:1 or 100to 50This is a turns ratio of 1.412:1Assuming the turns ratio is the impedance ratio.DM ImpedanceModeling ResultsThis has the correct DM Impedance of 100CM ImpedanceThe input impedance for CM signals is 50This is flawedThe target value for CM impedance is 25This can be fixed by placing a 50in parallel with the CM output port.The impedance ratio of 2:1 is challenging to achieve in practice because it requires a turns ratio of root 2, 1.412, to 1Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 03, 2020, 03:08:39 pm
content: Hi Group,The next product that I am going to look at is the Tekbox TBLM1.A friend of mine sent me a couple of photographs of the PCB inside the TBLM1. The schematic is the same as the circuit used by Sanjaya Manitala in the EDN article. The transformer is a Mini-Circuits ADT1-6T+.The datasheet can be found here:https://www.minicircuits.com/WebStore/dashboard.html?model=ADT1-6TThis is a 1:1 transformer with a center tap.Based on the -3dB point (30kHz) I am assuming an inductance of around 200uH.There are no other components in the box.CM ImpedanceThe TBLM1 has a CM Impedance of 50This is a flaw. The CM Impedance should be 25\$\Omega\$DM ImpedanceThe differential mode impedance is 50This is a flaw. The DM impedance should be 100The TBLM1 has the wrong impedances for both CM and DM signals.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 03, 2020, 03:43:51 pm
content: Hi Group,So far I have shown a few circuits that don't work properly. It is now time to show one that does work properly. I found this information published by Virginia Tech CPES.This circuit is a little more complicated. It uses two transformer and two resistors. The transformers are both 1:1 which makes them easier to wind.CM ImpedanceResultsThis circuit gives the correct result which is 25DM ImpedanceThis circuit gives the correct result which is 100We have found a circuit that works !!It give both correct impedance for DM and CM signal paths.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 03, 2020, 04:09:33 pm
content: Hi Group,Now that we have a schematic that looks promising, it is time to design and construct a prototype.KICAD SchematicBoard Artwork50Coplanar waveguide over a ground plane is used to control the impedance on the board. The design is kept a symmetrical as possible.Board DesignMechanical PackagingFusion 360 was used for the mechanical design. The housing is a piece of extruded aluminium.Regards,Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: July 03, 2020, 05:24:41 pm
content: This looks great. What about ready made RF 1:1 transformer such as CoilcraftPWB1010L_? It has 780 uH instead of 330 uH, but looks equal in simulation (attached)?

author: floobydust
author_rank: Super Contributor
timestamp: July 03, 2020, 05:46:42 pm
content: I looked into making transformers for one back herehttps://www.eevblog.com/forum/rf-microwave/help-making-a-wideband-transformerbut couldn't decide on a core material or stack.Schematic taken from Electromagnetic Compatibility Engineering by Henry W. Ott pg. 707 that usesRFMD Sirenza Microdevices LF-428excellent but obsolete and super expensive.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 03, 2020, 07:01:12 pm
content: Hi Prasimix, Floobydust and the group,I haveasolution for the transformers. I wound it myself. I have finished the DM/CM separator and tested it. I am getting good results.I am writing in installments so you can follow the journey.The journey has been modified from the journey I took, but the segments are being strung together so they are easy to follow.Quote from: prasimix on July 03, 2020, 05:24:41 pmThe simulation is for two 100% coupled ideal inductors. The model doesn't include parasitic capacitance, self-resonance, core loss, copper loss, coupling, skin depth permeability versus frequency etc. etc.In the model the requirement is that the inductance is 'large' compared to the LISN inductance.In the next segment I will talk about the transformer.After that I will talk about the measured results.I was looking for certain properties in the transformer beyond turns ratio and all the usual stuff. If you want to think about this, think about the 'NVT' that was discussed in this thread:https://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/msg1662917/#msg1662917Regards,Jay_Diddy_B

author: hugo
author_rank: Regular Contributor
timestamp: July 04, 2020, 03:58:28 am
content: The KICAD Schematic is missing ...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 04, 2020, 05:38:46 am
content: Heh, the winding schedule will be more important.Though not too troublesome at these frequencies (<=30MHz ish).Tim

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 04, 2020, 12:34:52 pm
content: Quote from: hugo on July 04, 2020, 03:58:28 amSomething is happening with the forum. It is very difficult to get the right pictures to stay in the right place.Here is the schematic:Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 05, 2020, 02:11:46 am
content: Hi,I am going to continue with the construction of the transformers.There are two transformers:They are both transmission line transformers and have a turns ratio of 1:1 but they have different transmission line impedances.Both transformer were wound on TDK H5C2 T16-4-8E cores. These cores may be hard to get. If there is enough interest I can try some other cores that are more readily available.H5C2 is a high permeability (10K). The datasheet says it is suitable for low frequency (50KHz) applications. But who reads the datasheet?Transformer T1This has a low impedance transmission line. It was made by winding twisted pair of 0.4mm diameter enameled wire around the core.Transformer T2This should have a transmission line impedance of 100.I used a twisted pair pulled from CAT5 ethernet cable.I measured the transmission line impedance using my Tektronix 11801 with an SD24.The measured impedance of the transmission line was 106.5For this measurement the transformer was connected to the TDR with 50and terminated with a 100resistor.The first part of the TDR waveform is the 50coax. The step is the transmission line wrapped around the ferrite core.The magnetizing inductance of these transformers at 20kHz is around 800uH.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 05, 2020, 02:32:03 am
content: Hi group,now I am going to share the test results.All the measurements were made with an HP8714C Network Analyzer. The data is from 300kHz to 200MHz.All unused ports on the LISN Mate were terminated with 50terminations.OSL port CAL was performed for reflection measurements.Thru CAL (Normalization) was used for transmission measurements.The Ports are called:LISN_1LISN_2These are the LISN inputsCMDMThese are the output ports for the Common Mode and Differential Mode signals.LISN 1An Ideal result would be an SWR = 1The measured SWR is close to better than 1.1 of most the range 0 - 200MHz.An Ideal result would be 50at all frequencies.The input impedance is close to 50\$\Omega\$.To be continued ...Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 05, 2020, 02:41:53 am
content: Hi,LISN_2The SWR is better than 1.1 over most of the frequency range.The impedance is close to 50over the frequency range.This is the same data presented on a Smith chart. Ideally the impedance should be a dot on the 50, the center of the chart.To be continued ...Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 05, 2020, 02:54:39 am
content: Hi,I am going to share the transmission measurements.LISN_1 to the Differential Mode Output.The nominal insertion loss is 6dB.There is additional insertion loss of 0.4dB up to 100MHz.At 200MHz there is 1.5dB loss beyond the 6dB nominal loss.LISN_2 to the Differential Mode Output.This path has insignificant insertion loss beyond the nominal 6dB to 100MHz.The path has an additional 1.5dB of loss at 200MHz.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 05, 2020, 03:07:05 am
content: Hi group,continuing with the Common Mode Rejection Ratio.A resistive power splitter was placed on the on the output of the network analyzer. The outputs of the power splitter were connected to the LISN_1 and LISN_2 inputs.Both inputs are being fed with the same signal.The Differential Mode output was connected to the input of the network analyzer.This is areally goodresult more than 30dB of CMRR over the range 0-200 MHzCommon Mode to CM OutputThis should be nominal 6dB.Almost no insertion loss to 50MHz and very acceptable results to 200MHz.Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: July 06, 2020, 04:43:29 pm
content: Thanks for all of your efforts. I am currently using the LISN Mate (resistive circuit) and have previously used the Sanjaya Maniktala circuit. They seemed to work reasonable well differentiating the signals. But, we only did some rudimentary testing to characterize the performance.From my introductory e-mag courses in college, I know that poorly matched transmission lines lead to power loss, reflections, and standing waves...but typically we talked about it in the context of a fast rise time square wave signal.What are some typical effects of mis-matched impedances in this case? Frequency shifts? Resonant peaking? Wrong amplitdues?Thanks.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 06, 2020, 08:42:31 pm
content: Quote from: TimNJ on July 06, 2020, 04:43:29 pmThe biggest problem is that the LISN no longer conforms to the standard that are published by the regulatory bodies.The limits for a 5uH LISN, as found in CISPR16-1-2 are +/- 20% about the nominal value:If you used the Tekbox TBLM1 the resistance is 25instead of 50.The errors you get depend on the impedance of the noise source, the length of the cables between the LISN and DM/CM separator and the frequency.Errors in the range of 6dB are possible.LISNs are used in other tests, such as bulk current injection.The real question is why not use a LISN Mate that is designed correctly?Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: July 07, 2020, 03:11:28 pm
content: Quote from: Jay_Diddy_B on July 06, 2020, 08:42:31 pmThanks. Makes sense. I suppose I'm saying that once you run a "normal" EMI scan (without separator box), you will see the "true" results anyway. Maybe my EMI work is not as detailed as yours, but typically I just use a separator box to check which peaks are DM and which are CM. It seems that even the LISN mate can do this.However, maybe I've been fooled by the existing designs and haven't even noticed. Maybe I've even wasted some time. It makes sense to get it right.So, one question about your transformer construction. Both appears to be 10 turns, bi-filar, with the main difference (that I can see) being the gauge/stranding of the wire. What's the effect of the different construction? Different winding to core capacitance? Different inter-winding capacitance? I guess more directly, what are you trying to accomplish by changing the construction slightly?Also, if I build this, I'll probably try jamming it in this enclosure:https://www.pomonaelectronics.com/products/boxes/shielded-box-size-b-225-x-138-x-113-4-bnc-f-blue-enamel-coverIt might be convenient for other people to use this enclosure too since it already has 4 BNCs, solder terminals etc.Thanks!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 07, 2020, 04:04:09 pm
content: Quote from: TimNJ on July 07, 2020, 03:11:28 pmHi TimNJ and the Group,The 'danger' of only using the LISN for DM/CM separation is that you forget and leave it in circuit for other tests. If the LISN Mate presents the right impedances it doesn't matter if you leave it in the setup all the time.For me it was interesting to see the differences between the schematics other people had used. If I was going to build one, I might as well get it right.To get good high frequency response, these transformer are transmission line transformers. The capacitive coupling cancels the leakage inductance.One of the transformers was wound with wire harvested from CAT5. This has a nominal impedance of 110 Ohms. This should be fairly easily to find.The other transformer is wound with magnet wire about 0.4mm in diameter. The two wires are twisted first. This transformer should be wound with a 50 Ohm transmission line.If you wind them differently, it will work but the separation will not be as good.The core is more challenging. I have had the cores that I used a long time. They may be obsolete, they are hard to buy in small quantities.A similar sized core in EPCOS T38 materialmightwork. I will add some cores to my next Digikey order.If you want to avoid the metal work the Pomona Box will be fine.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 08, 2020, 03:10:18 am
content: Hi group,I spent most of the day designing and building a clone of the HP35676A Reflection/Transmission Test Set. This work with the HP3577A Network Analyzer. I will described the design and construction of the RT Test Set in another thread.I have the S-parameter Test set, but this has a lower frequency limit of 100kHz.The RT Test Set will work down to 5Hz.DM Impedance MeasurementsThe target impedance is 100The measure impedance was 97-3dB point isCM Input ImpedanceThe target impedance is 25And at low frequenciesThe theoretical number should 12.5The measured impedance for DM and CM signals is very close to the values expected.The low frequency corner is sufficiently low, so it will not impact EMC measurements.Regards,Jay_Diddy_B

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 08, 2020, 04:12:37 am
content: Another option for getting close to 50 ohms is a twisted pair-plus. Twist three wires, say wire-wrap or CAT-5 stuff (peeled apart if needed), and connect two of the strands in parallel. This gives an unbalanced E-field, which doesn't really matter for such a short winding (the effect will be poor DMRR, but at very high frequencies where it doesn't matter).It's not easy to calculate or look up transmission line geometries like this; it's easier to get an estimate with a 2D calculator. ATLC2 comes to mind, particularly being easy to use, just feed it a BMP of adequate size and the right colors, and it calculates the quasi-static field distribution, and the impedance, for one or two conductors with respect to ground. (So, it can't take into account skin effect and dielectric loss, but for well-behaved materials, those should amount to small adjustments.)Tim

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 08, 2020, 11:17:25 pm
content: Quote from: T3sl4co1l on July 08, 2020, 04:12:37 amHi Tim and the group,I did a little experiment using my HP3577A VNA and my clone of the 35676A R/T Test Set.If you are interested in the 35676A clone have a look here:https://www.eevblog.com/forum/testgear/cloning-the-hp35676a-reflection-transmission-test-set-for-the-3577ab-vna/msg3126330/#msg3126330ExperimentThe transmission line transformer was connected to a small 200trim pot. The other end of the transformer was connected to the T/R test set.SOL calibration was performed at the point where the 50 coax was connected to the transmission line.The Smith chart was observed while adjusting the variable resistor.The variable resistor was adjusted until the circle displayed on the Smith Chart was a small as possible.At this point the resistance of the variable resistor is equal to the transmission line impedance, Z0.The dot on the Smith chart is close to 2, indicating 2x the nominal impedance, 2x 50.I then disconnected the RT Test Set and measured the resistance with a DMM. The resistance was 110.This is the same value I got using TDR and the characteristic impedance of the twisted pair in CAT5.Two transmission lines in parallelI then tried measuring two twisted pairs, about 1m long, connected in parallel. I twisted the twisted pairs together. I measured the Z0as 50. This is probably a good result because there is a little extra capacitance from twisting the two 110pairs together.Two pairs from the ethernet cable will not fit on the small cores.I can use the technique with magnet wire to measure the impedance of the transformer.It is probably easier to measure than modeling impedance.Regards,Jay_Diddy_B

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 08, 2020, 11:47:18 pm
content: Another good way to measure it.Yeah, two twisted pairs in parallel will do; and, it won't matter for short windings like these, but long windings like the injection transformer, may want to be aware of something: the pairs in Ethernet cable are intentionally twisted at different rates, which gives them slightly different velocities. It may be desirable to use just one pair for all windings, take a length, cut it in half, wind those in parallel.For very low impedances, there is a particular pattern: star quad. Take four strands and twist them together; looking at the bundle end-on, going around the circle: connect the strands alternately to + and -. This gives a quadrupole arrangement which gives about half the impedance again -- i.e. about 25 ohms for this type of wire!(A pretty handy tip, when you need transformers with an impedance give or take a factor of 2 from 50 ohms -- 25 and 100 ohms are common needs.)(For even lower, I would suggest parallel-plate transmission line, built with flex or tape. Or use lots of pairs/quads wired in parallel.)Tim

author: TimNJ
author_rank: Super Contributor
timestamp: August 20, 2020, 02:01:02 am
content: @Jay_Diddy_BDue to the whacked out image attachment situation, can you attach the functional schematic (with inductors shown) one more time? Maybe just try a regular ol' attachment, and no inline image.Thanks!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 20, 2020, 02:33:10 am
content: TimNJ,Let me try again:Have also attached a pdf version.Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: August 20, 2020, 11:07:46 pm
content: @Jay_Diddy_B..The Virginia Tech circuit, as far as I can tell, uses a 3rd transformer for impedance matching 25 ohm to 50 ohm, hence the sqrt(2): 1 turns ratio. But, in your circuit, seems you terminate the Zo = 100R transmission line transformers into 50R.Also, I have no idea what I'm talking about.Just wondering what's going on there.Thanks.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 20, 2020, 11:59:49 pm
content: TimNJ and the group,In this circuit:The function of T1 is the same as in the one I built. Rintis 50so when the spectrum analyzer is connected the common mode impedance is 25. This is Rint// Spectrum analyzer.T3 in this design is a common mode choke. It references the differential signal between A-B to ground. So it is a balun, balanced to unbalanced. The differential impedance between A and B should be 100. T3 should be built with a 100transmission line.T2, with a turns ratio of 1.41 : 1, has an impedance ratio of 2:1 matching the 100to the 50of the spectrum analyzer.The transformer would have to be approximated to 3 : 2 or 7 : 5In the one I built R2 and the 50load, the spectrum analyzer are essentially in series, making a 100differential load. There is a 6dB reduction in the signal, half the signal on R2 the other half on the spectrum analyzer. But I don't need the third transformer. There is also better symmetry.Does that help?Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: August 21, 2020, 12:39:32 am
content: Thanks for your explanation and clarification. So, the DM output signal is attenuated by 6dB, but the CM output signal is ~0dB? If that's the case, I'd almost prefer to put a 6dB pad on the CM signal.Just thinking about how I typically approach EMI debugging...I might want the signals to at least be scaled to each other. (Perhaps in situations where you have CM and DM overlapping.)Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 21, 2020, 02:28:17 am
content: Rint is 25 ohms, so if you use 50 ohms in parallel with the receiver's 50 ohms, you lose 3dB (power) to that, but 0dB voltage, and 6dB current.Same for DM: it's down by 3dB (power), but 6dB voltage, and 0dB current.So, depends on which mode and impedance you're calibrating to, and if you're more interested in voltage/current or power.Tim

author: TimNJ
author_rank: Super Contributor
timestamp: August 21, 2020, 04:35:24 am
content: Quote from: T3sl4co1l on August 21, 2020, 02:28:17 amThanks much. I still don't have an intuitive grasp on a lot of these fundamentals...clearly. For CM, I'm a bit perplexed that the voltage at the receiver wouldn't drop by 6dB if the equivalent resistance across the receiver is 25R as opposed to 50R.The receiver measures in dBuV since the EMI limits are specified as such. It would be nice if you could get the actual level (maybe with the exception of -0.5-1dB insertion loss).I'd like to re-iterate that I punching above my weight, but is this vaguely what the matching circuit would need to look like? Could Coilcraft PWB (https://www.coilcraft.com/getmedia/2623c26b-542e-49f8-90ee-c7b1fe27d34b/pwb.pdf) work if using the 1:2 part?I appreciate all of your guidance (and patience with me).

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 21, 2020, 05:32:14 am
content: Hi TimNJ,If you don't use a DM / CM Separator and you connectoneof the LISN directly to the spectrum analyzer you will measure half the DM mode noise.So you read -6dB down.This is because the other LISN is terminated in a dummy load.So being -6dB isn't necessarily a bad thing.Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 21, 2020, 06:02:28 am
content: Quote from: T3sl4co1l on August 21, 2020, 02:28:17 amTim,Rintis not 25Rintin parallel with the spectrum analyzer = 25.The CM impedance should be impedance of two LISNs in parallel.Similarly the DM impedance is two LISNs in series.It is how the EMC specifications are written. The EMC specifications specify that you use two LISN and you measure them individually. The EMC specifications do not distinguish between CM and DM noise.There are several schematics published by VPEC, this one from the patent application, I believe to be correct:The patent has expired:(BTWI agree that Z0on T2 is 100.I don't agree that Z0on T1 should be 50. The reason I don't agree is because the signal is flowing in opposite directions in the transformer windings. The impedance of the transformer looks a shorted transmission line, half the electrical length of the winding. The transformer should be as small as possible, while achieving enough inductance. This minimizes the length of the line.)Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: August 21, 2020, 06:06:31 am
content: Ah! Well now it sounds so obvious. So, the output of the separator’s DM port is 6dB from the actual level, but that’s no different than the normal measurement...so actually no problem at all.Now it’s time to get on with building it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 21, 2020, 06:18:43 am
content: I was referring to this one,(Which in the CM-DM separator, Rint is 50R || spec.)Tim

author: TimNJ
author_rank: Super Contributor
timestamp: November 06, 2020, 09:34:44 pm
content: Hi,I'm testing my version of the separator. Does it make sense that I'm getting -6dB insertion loss from LISN1 (or LISN 2) toCM Out, when I apply a signal to LISN1 OR LISN2 (not simultaneously)? The result from LISN1 (or LISN2) to CM Out is actually the same as the result from LISN 1 (or LISN2) to DM Out. My intuition says that very little signal should arrive at CM out...but that doesn't seem to be the case. On the other hand, when testing with a resistive splitter (to inject a common-mode signal), I see -30dB at the DM Out port, and -6dB at CM out...which makes sense in my mind.All unused BNCs capped with 50-ohm terminators.What gives?Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 06, 2020, 09:45:18 pm
content: Normal mode (just one port) divides evenly between CM and DM, so both should be -6dB each.Tim

author: TimNJ
author_rank: Super Contributor
timestamp: November 06, 2020, 09:58:27 pm
content: Thank you, Tim. I think I understand. If you wanted to directly test the rejection of DM at the CM Output port, would you need to drive both inputs, but one 180 degrees out of phase? Maybe with a 180 degree splitter?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 07, 2020, 03:52:06 am
content: Exactly.Well, depending on which one you're measuring and rejecting. I'm not sure I understand which one you're talking about. But driving them in-phase is common mode and rejects differential; opposite-phase is differential mode and rejects common.Can also do it the other way, drive the DM or CM port and check the balance (amplitude and phase) on the ports.Tim

author: uski
author_rank: Frequent Contributor
timestamp: November 07, 2020, 07:07:27 am
content: Hi !Soafter having success with Jay_Diddy_B's LISN design, I find this topic... and I would love to try to build myself one of these "LISN mate"!Quote from: Jay_Diddy_B on July 05, 2020, 02:11:46 amAs expected this core is nowhere to be found. Is there a more readily available core I could use ?Something like this maybe ? But I can't even find the specs of the original cores used so I don't know if this is correct either magnetically or physicallyhttps://www.digikey.com/en/products/detail/ferroxcube/TX29-19-7-6-3E6/8021257

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 07, 2020, 02:12:25 pm
content: Hi,The TDK Part No H5C2 T16-4-8ECan be decoded:H5C2is the materialTis the shape, toroid16is the outside diameter in mm4is the thickness mm8is the inside diameter mmEis the coating, epoxyThe 3E6 materialmightwork.T38 is another material thatmightwork.I bought some T38 cores B64290L0044X038.I haven't tried them.Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: November 07, 2020, 03:04:06 pm
content: Quote from: T3sl4co1l on November 07, 2020, 03:52:06 amThanks again! I may try both ways. We’ll see.Quote from: uski on November 07, 2020, 07:07:27 amI have built my own version with JDB’s recommended core. I’ve also purchased alternate cores from TDK and Ferroxcube. I will test them soon and leave an update here. I also have a PCB design I can share.

author: bluesky1688
author_rank: Newbie
timestamp: December 01, 2020, 04:26:47 pm
content: Hi All,I'm not a transformer or an EMC person but tasked to understand the FCC conducted and radiated emission test. So, any help with this task would be greatly appreciated. Fortunately I stumbled upon this excellent site with so many subject matter experts.I first started looking for the now obsoleted LF-428 transformer with no luck then found this site. Is the TEKBOX setup cited in the following EDN article the, post LF-428, modern way to go?https://www.edn.com/review-tekbox-lisn-mate-is-valuable-for-evaluating-filter-circuits/Thanks,William

author: Noy
author_rank: Frequent Contributor
timestamp: December 23, 2020, 01:05:26 am
content: QuoteWould you like to share your pcb files here? Are they kicad? Would like to build this "lisn mate" but i will use a 1590B case.

author: TimNJ
author_rank: Super Contributor
timestamp: December 29, 2020, 03:07:06 am
content: Greetings. Sorry for the delay on this. I've been so busy with many things that this got sidelined. However, I have tested my PCB design with a VNA, using the original prescribed TDK H5C2 cores, and the performance is on par with JDB's measurements. I've measured impedance, DM rejection, and CM rejection. Sorry I don't have the plots right now, but I can assure you it looked good. I will get the plots for H5C2 and the other core materials soon.I've already designed it for Hammond 1590G. I'd recommend to just use the 'G' version. The size is a little smaller than the 'B' version with I think is a good thing.Please see the attached zip.The BOM is very simple:(Qty. 1) 10 turns twisted pair 0.4mm enameled copper wire on H5C2 T16-4-8E core(Qty. 1) 10 turns twisted pair from CAT5 cable on H5C2 T16-4-8E core(Qty. 4) TE/AMP 5-1634513-1 (PCB mount BNC jack)(Qty. 2) 49.9Ohm 0603 resistor (I used MCT0603PD4999DP500, 0.5%, 25ppm, 1/4W)I used JLC black soldermask. It looks nice with the black version of Hammond 1590G.I built mine on my R01 version PCB. Works fine, but I made the holes for the 4 posts (for each BNC shell->PCB connection) too large. It made the alignment tricky during soldering. I've fixed that in the R02 PCB file, attached.

author: coppercone2
author_rank: Super Contributor
timestamp: December 29, 2020, 09:03:35 am
content: the torroid outline with the transformer symbol nearby it reminds me of something

author: Noy
author_rank: Frequent Contributor
timestamp: December 29, 2020, 11:32:06 pm
content: Hi, unfortunally i couldn't get the suggested: H5C2 T16-4-8E ones.I bought the "maybe" ones (B64290L0044X038) from Mouser and hope they are useable.I already have 1590B cases (pretty cheap on aliexpress (1,60€ for one..)) so i will use it and have to do a new board / modify yours.I will use SMA connectors, have only a very small amount of BNC cables here ...How critical are these:10 turns twisted pair 0.4mm enameled copper wire ?Are 0.4mm a "have to"? Can i use other cables?How do you tighten the cores to the PCB? So that they aren't flapping around? Maybe 3 soldertabs and "desolder braid" to fix them onto the pcb?I will use cherrypicked (4 wire measured) 0805 49.9 Ohm resistors (have them already here..)

author: TimNJ
author_rank: Super Contributor
timestamp: December 30, 2020, 12:02:19 am
content: Quote from: Noy on December 29, 2020, 11:32:06 pmRegarding the 0.4mm diameter wire, hmmm, I'll have to let Jay_Diddy_B or T3sl4co1l (et. al.) answer that one definitively. They are designed as "transmission line transformers", that is, maintaining some characteristic impedance that depends on wire to wire spacing, twists per unit length, etc. If I had to guess, you can deviate a little, but I'll let them answer..Regarding fixing the cores, I too considered implementing some sort of "proper" way to fix the cores to the PCB. I considered adding slots for zip-ties, even small hole for nylon screw + nut. But, I opted just for regular old non-corrosive RTV silicone (can also use some decent hot melt glue). The cores are light enough that I don't think it's really worth doing anything elaborate.I would be hesitant to recommend adding something conductive/magnetic to fix the core to the PCB, as I can't be certain the effects it may have on high frequency performance.Does your LISN have SMA connectors? Just thinking that the reason this is designed with BNC is that the vast majority of LISNs with RF output ports use BNC anyway.

author: Noy
author_rank: Frequent Contributor
timestamp: December 30, 2020, 12:15:01 am
content: My LISN has ;-)Reworked Jay_Diddy_B's LISN:https://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/75/You are right, will use hot glue to mount the cores.And with the 0.4mm wire i will check if i have something here, else i have to purchase one from aliexpress / mouser.Can you post a picture from your winding?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 30, 2020, 11:44:06 am
content: As long as the wire length is short, and the turns fit through the core, you're fine.Wire-wrap wire, pairs from Ethernet cable, etc. are also good candidates -- give or take exact impedance required of course. I think... one of them should be lower and the other should be about that impedance (insulated twisted pair)? But if you use magnet wire or insulated for both it's not going to be too far out.Tim

author: Noy
author_rank: Frequent Contributor
timestamp: January 18, 2021, 12:52:03 pm
content: Here are my design files, hasn't build it up completely yet. Still missing the copper wire (on its way from china)..Also for china Hammond 1590B cases

author: Knuddel
author_rank: Contributor
timestamp: January 18, 2021, 08:40:17 pm
content: Hi Noy,if you do not heasitate ordering from the big "a" you can serch for "Block Kupferlackdraht Basteldraht Schmuckdraht Kupfer-lackdraht Kupferdraht Wickeldraht Kupfer Draht Cul 100/0.40".Unfortunately I have ordered the PCBs with BNC-jacks, now.This fits in a 1590G case that is smaller but straight BNC print jacks are not easy to buy and I need to get some adapter cables to attach it to your LISN design with SMA, that I preferred.I should have waited for your final data from your last post #52. That comes for the larger 1590B case but has SMA-jacks...

author: Noy
author_rank: Frequent Contributor
timestamp: January 29, 2021, 12:55:09 am
content: My 0.4mm Cooper wire arrived.Would somebody share a picture of their working wire wound?10x twisted 0.4copper and the other 10x twisted cat5 cable? Or cat5e?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 29, 2021, 02:21:38 am
content: Quote from: Noy on January 29, 2021, 12:55:09 amNoy and the group,Pictures of the transformers can be found in this message:https://www.eevblog.com/forum/projects/diy-dm-cm-seperator-for-emc-lisn-mate/msg3120176/#msg3120176I will reproduce them here:Jay_Diddy_B

author: Noy
author_rank: Frequent Contributor
timestamp: February 06, 2021, 03:14:29 pm
content: THX, wire arrived. Completed the build but measurment are still not done yet..I think the cores are smaller than yours was a bit thightly to get the 10 windings of cat5 wire onto the core but it fits.Unfortunally i cannot do TDR measurments.. Would Luke to have a sampling scope but too expensive currently..Have to find out how i can do it with the VNA..

author: TimNJ
author_rank: Super Contributor
timestamp: February 17, 2021, 05:23:00 pm
content: With a VNA, you can make these measurements:1. Impedance and SWR of each LISN port2. Common-mode rejection3. Differential-mode rejectionFor all measurements, if you are not directly using a port (SMA or BNC), it should be terminated with a 50 ohm termination.Ideally, when LISN 1 and 2 are driven with a purely common-mode signal, there should be almost no signal at the differential-mode output, over the entire frequency range. You can drive both inputs with an in-phase signal by connecting the output of the VNA to a resistive power splitter, i.e. Mini-Circuits ZFRSC-42-S+.And, when LISN 1 and 2 are driven with a purely differential-mode signal, there should be almost no signal at the common-mode output, over the entire frequency range. You can drive both inputs with a 180-degree out-of-phase signal by using a hybrid power splitter, i.e. ZFSCJ-2-2-S.

author: Knuddel
author_rank: Contributor
timestamp: February 19, 2021, 05:44:08 pm
content: Hi! (What is the trick to get the pictures in line with the text? OK, thanks Tim! Is it possible to keep them at default tumbnail size and only load to full size by mouseclick?)in the meanwhile my BNC-sockets arrived from china as I missed to order the cheap TE 5-1634503-1 from Mouser when I ordered all other components for Mate and Lisn.I measured the transmission behavior with Scope Bode Plot function:When measuring it from Lisn2 In to CM Out it's like this: (result -6dB)Same but leaving DM-port unterminated: (result -9dB)When measuring from Lisn2 In to DM Out: (result -6dB)(seems there is some signed integer treated as unsigned somewhere in the MSO5000 Bode Plot script when phase flips over 180°)When measuring from Lisn1 In to CM out: (result -6dB)From Lisn1 to DM out: (result -6dB)(Why does it shows a higher edge frequency? Is there an impedance discontinuity because of too much twists in the copper ends near the solder pads? Or should I remove the last winding form CAT5 because it fills the hole in the core and coulpes in to the other side?)Seems that these cores are close to the TDK ones, are they?When measuring the whole path from DUT+ and DUT- throughthe forums final double Lisn with -10dB attenuators inside andthrough the Lisn-Mate to CM out I've got the following results:(I guess it is -6dB because the signal was divided by 2 when feeding it to DUT+ and DUT-,but why isn't it -10dB-10dB-6dB-6dB=-32dB)When measuring the whole path from DUT+ and DUT- to DM out: (-3dB ?)There first I thought something went wrong, but on the other hand it reflects somehow the overlay of both DM-plots above.P.S.: I had have only one BNC termination and used a 25cm BNC to SMA cable with a SMA termination at the end for second termination. For third termination I simply connected the Lisns SMA output to the port. You find the termination type in the file names for each plot.For noise measurements I am still wondering how I have to set my correction level in the spectrum analyzer with the different setups:1 Lisn with -10dB attenuator no mate +10dBµV (add 10dB noise)2 Lisn with -10dB attenuator no mate +16dBµV2 Lisn with -10dB attenuator mate DM out, CM terminated +3dBµV2 Lisn with -10dB attenuator mate CM out, DM terminated +6dBµVThis is what the scope plot tells me, but the scope shows a dB relation between two peak ac voltages, how does it fits to the absolute dBµV ?I guess as this is also relation of voltage to 1µV, it fits very well, right?But as the CISPR standard does not distinguishes between CM and DM and only measures with two Lisn the output of one of themdo I have to compensate anyhow or is the -6dB included into the standard?And as Jay_Diddi_B writes in post #21 that this Mate stuff is only for interest on the way to find the noise source but with correct design could stay in the setup,then I should have to compensate the SA in the same way as without Mate like this:1 Lisn with -10dB attenuator no mate +4dBµV2 Lisn with -10dB attenuator no mate +10dBµV2 Lisn with -10dB attenuator mate DM out, CM terminated +10dBµV2 Lisn with -10dB attenuator mate CM out, DM terminated +10dBµVPlease correct me if I am wrong!For me it's same: "Also, I have no idea what I'm talking about."And: "I appreciate all of your guidance (and patience with me)."Kind Regards,Hanno

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 19, 2021, 08:03:47 pm
content: After posting, right-click copy link address on an attachment (at default thumbnail size) and paste inside an img tag. The inline thing was, half ass disabled I guess, not just removed, because image cache was getting corrupted or something.Tim

author: HallWu
author_rank: Newbie
timestamp: February 17, 2022, 01:53:56 am
content: Quote from: Jay_Diddy_B on July 08, 2020, 03:10:18 amDear Jay_Diddy_B,Thanks for your excellent work on LISN Mate, that helps me a lot. If I want to move the corner frequency below 10kHz, should I increase the inductance of T1 and T2? To be more specific, should I increase the turns of T1 and T2 from 10 to 15? Dose the copper below the T1 will affect the CMRR of DM_out port? I have tested the CMRR of DM_out port based on the paper ‘Characterization, Evaluation, and Design of Noise Separator for Conducted EMI Noise Diagnosis’ , but it is only -30dB at 150kH~30MHz. What should I do to improve the performance of CMRR at DM_out port? I am looking forward to your reply.Best wish,Jerry.

author: Smokey
author_rank: Super Contributor
timestamp: April 15, 2023, 09:36:13 am
content: What did you guys decide about alternate cores that you can actually get? What are the best ones?