Ever since we switched from incandescent lamps to LED lighting, from linear power supplies to switch-mode power supplies, EMI on the power cord began to become a problem, especially for AM radio stations and amateurs who still like medium wave and medium wave bands. For the people on the radio. HF spectrum (0.54 to 30 MHz). Coupled with faulty electric utility transmission lines arcing and corona, many amateur radio enthusiasts and military operators simply cannot receive national and international radio stations through the hash generated on the receiver.

I wrote an article in 2015 on how the police used AM radios to find a "growing business", about how people who illegally grow cannabis buy poorly filtered power sources ("ballasts") from Asia for lighting. The EMI generated by these power supplies has a wide range, up to 1 mile, and the police in Oakland, California realized that they could hear the hashing sound through AM radio, which allowed them to zero these growth operations.

Because this kind of broadband high-frequency electromagnetic interference is conducted and radiated, it is difficult to eliminate at this point in time; the unexpected consequence of the desire for more efficient power supplies. At the same time, those who use these frequencies are suffering the consequences.

OnFILTER recently released a power line EMI adapter that can be used with a spectrum analyzer or oscilloscope to evaluate conducted power line EMI (Figure 1). Their devices can be plugged directly into wall sockets or sockets with test leads. I was able to evaluate it with the test line because it seemed more versatile. The test leads and accessories are of high quality and manufactured by Pomona.

Figure 1 OnFILTER's new MSN15 power cord EMI adapter and test leads can be used to evaluate conducted power cord EMI.

When used with a spectrum analyzer, they recommend inserting a 20-dB attenuator in the input port. For use with an oscilloscope, they provide a BNC T-type adapter with a 50 Ω load. I suspect that if your oscilloscope is set to 50 Ω, you don’t need the latter, as most people do.

Since the device is galvanically isolated from the AC power source, the input lead can be connected between any two connections without worrying about the ground reference. The maximum rated voltage is 250 VAC, and the frequency response of the adapter is 30 kHz to 200 MHz. It can display most power line communication (PLC) records, such as Homeplug AV and AV2, G.hn Wave 2, CENELEC EN50065 (all frequency bands), IEEE 1902.2 and ARIB (Japan).

Although most usage modes can be performed with an oscilloscope, I would like to try it with a spectrum analyzer. I also have a Solar 7032-1 isolation transformer and an OnFILTER AFN515FG CleanSweep power line filter to see how they can effectively reduce the conducted EMI from my own power line (Figure 2).

Figure 2 This is used to compare and test the settings of Solar 7032-1 isolation transformer and OnFILTER AFN515FG CleanSweep EMI filter.

The results are very interesting (Figure 3). On the one hand, I didn't realize how "dirty" my own power cord was. Adding an isolation transformer helps a lot, but the CleanSweep filter reduces most of the EMI to the analyzer's noise floor, at least 12 MHz (this is the upper specification limit).

Figure 3 The frequency domain scan from 100 kHz to 100 MHz shows my power cord (purple), Solar 7032-1 isolation transformer (blue), and OnFILTER AFN515FG EMI filter (green).

The broad peak of approximately 15 to 80 MHz is likely to be an environmental factor and may be directly coupled into the long test lead. I haven't investigated this yet. Placing a ferrite choke around the two test leads did knock them down. Figure 4 shows an example Homeplug-AV2 spectrum on the power cord.

Figure 4 This is an example of the Homeplug-AV2 spectrum on the power cord. Source: OnFILTER

Now turning to time domain capture, let's look at the old X10 remote controller using the MSN515 adapter and extend the time extension (Figure 5). PLC is easy to view.

Figure 5 This is a time domain capture of one of the old X10 remote controls using MSN515. Source: OnFILTER

This is another example of servo motor EMI in an industrial environment (Figure 6).

Figure 6 This figure shows the EMI of the servo motor on the power line in an industrial environment. Source: OnFILTER

In general, I am very impressed with the EMI adapter and CleanSweep filter that I can try. In addition to power line EMI monitoring and evaluation, I am still considering its use. I suspect that it can also be used to measure different "grounding" points in large industrial systems, or even to measure EMI on ground loop planes or power distribution networks.

Of course, using one of OnFILTER's CleanSweep filters can well reduce or eliminate transient EMI pollution from power lines from welding stations or industrial machines that use servo or variable speed drives.

Due to the proliferation of switch-mode power supplies, I do hope that some measures can be taken to solve the general increase in EMI on power lines. Maybe I should start replacing all switch-mode power supplies with linear power supplies, as a friend did to improve the background EMI of his long-range radio astronomy observatory!

—Kenneth Wyatt is the President and Chief Consultant of Wyatt Technical Services.

How to mark the price?

Sorry, it should be included. MSN15 (with test leads, reviewed) is 485 USD. MSN17 plugged into a wall outlet is $425.

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