Tag Archives: Switching Power Supply Noise

Guest Post: Indoor Noise and Ferrites, Part1

Many thanks to SWLing Post contributor, TomL, who shares the following guest post:


Indoor Noise and Ferrites, Part 1

by TomL

My magnet wire loop antenna on the porch reminded me to revisit aspects about my noisy Condo that I still needed to understand.  Some RF noise I could control if I could find the right kind of information that is understandable to a non-engineer like me.  There is a lot written about the general problem of noise and radio listening, for instance this ARRL article with web links to research – www.arrl.org/radio-frequency-interference-rfi, but I needed to get more specific about my particular environment.

I had tried some common clamp-on TDK ferrites I had obtained from eBay a long time ago but they only seemed to work a little bit.  I have since found out these are probably the ones which are widely used on home stereo system connections used to reduce noise on those systems.  There must be a better way.

The more I researched topics, like a portable “Loop on Ground” antenna, or, using RF chokes on the magnet wire loop, it dawned on my feeble, misguided brain that I was wrongly thinking about how to use ferrite material.  For one thing, the material used to suppress RF noise is made with a certain “mix” of elements, like Manganese-Zinc, that electrically “resists” a specified frequency range.  Fair-Rite has a useful Material Data Sheets web page which lists the Types of ferrite material.  For dealing with noise (at the Source causing the problem), I needed to use the right kind of “Suppression” materials and proper placement.  So, it (partly) made sense why the TDK snap-on ferrites might not fully work to reduce certain noise coming from my computer screens, LED lights, USB devices, and cheap Chinese-made power adapters.

A very good  paper is by Jim Brown (K9YC) of Audio Systems Group entitled, “Understanding How Ferrites Can Prevent and Eliminate RF Interference to Audio Systems [PDF]”.  There is a longer paper speaking directly to Amateur Radio folks, but the Audio version is simpler and it uses some of the same  graphs and ideas.  I was drawn to the very detailed Impedance measurements of many different “Types” of ferrite material used for different noise mitigation.  I remember the traumatic pain of my college experience trying mightily to understand the Van Vlack Materials Science text book to no avail.  But Jim’s paper reminded me of the importance of using the correct type of ferrite material and in an optimal way that reacts favorably in the target frequency range to solve a particular noise problem.  So, what are my problem areas?

Shortwave Noise

Loop antennas have been what I have experimented with the most.  They do not pick up as much man-made noise (QRM) and they have a space saving footprint.  Fortunately, there is a wooden porch where these things have been tried.  I had successfully built a broadband amplified “ferrite sleeve loop” (FSL) in the past.  It was useful for a while but it fell into disrepair and also the Condo building has steadily increased in noise output.  The amplifier was just amplifying the noise after a while.  I also tried phasing two antennas but found the ever increasing noise cloud was coming from all directions and I could not null it out.  I even tried a “mini-whip” from eBay but that just produced a wall of noise.

I recently tested AirSpy’s YouLoop written about before, and the results were good.  However, it seemed obvious to me that it was too small as a passive loop to capture shortwave signals strongly enough without resorting to another amplifier attached at the antenna and would not improve the signal/noise ratio.  My current solution is a unamplified stealth magnet wire loop about 32 feet in circumference.  In that article, I mention things like common mode RF chokes at both ends of the antenna connection, horizontal polarization, and basically accepting that only the stronger shortwave signals will be received in a predictable manner.  I think for now, this is about all I can do for shortwave and mediumwave noise, as far as my own Condo-generated noise. Neighborhood noise is a different topic.

VHF Noise

I then started to isolate which devices caused which kind of noise when listening to my outside amplified antennas for FM/VHF and UHF-TV transmissions.  Many consumer Power adapters make a lot of noise from VLF up into UHF ranges.  One thing I did right was to try a 10 pack of these little miracle “Wall Wart” toroids from Palomar Engineers.  One by one, I put one of these small toroids (19mm inside diameter) on my home AC adapters as shown in the pictures, and the noises started disappearing.  It does not explicitly say, but I believe it is Type 75 material which suppresses the noise generating AC adapter (at very low frequencies) when wrapped 8 – 12 times.

Most egregious of these was my CCrane FM2 transmitter.  A strangled warbling sound kept emanating from the monitor closest to my laptop. Installing ferrites on the laptop and back of the monitor were not working.  I moved the FM Transmitter and noticed a reduction in noise.  So, I put one of these little toroids on the power input of the device and the noise disappeared.  Apparently, it was picking up noise from the monitor (as well as its own power adapter) and rebroadcasting it to all my other radios!  The strangled warbler is no more, I choked it (HaHa, sick bird joke).

While looking for the monitor noise, I put the eBay TDK ferrites on all the USB ports and HDMI ports.  This has helped greatly on VHF and confirms my suspicion that these cheap TDK ferrites are indeed a common type of ferrite material.  Some informative graphs can be seen in Jim Brown’s Audio paper mentioned before.  One example might be Figure 22, which shows the #61 Series Resistance which peaks around 100 MHz when using a toroid with three “Turns”.  More confused, I could not find a definition of a “Turn”.  Eventually, in his longer paper to Amateur Radio operators, he defines it, “…is one more than the number of turns external to the cores”.  Somewhere else he describes using many single snap-on ferrites being electrically equal to just one toroidal ferrite with multiple Turns.  And interestingly, more Turns shifts the peak impedance substantially lower in frequency.  So, using the graphs he supplies, one can target a noisy frequency range to try to suppress.

I then put 6 of the TDK ferrites on the VHF input to the AirSpy HF+.  Some FM grunge was reduced and was thankful for that.  The rest of the background noise truly seems to be coming from the outside picked up by the amplified antenna.

Also, I juggled a couple of the amplifiers around and now have separate VHF/FM and UHF/TV amplifiers which cleaned up the FM reception a little bit more – https://www.youtube.com/watch?v=zkDsy95et2w .

UHF TV Quality

On a whim, I put the balance of the TDK ferrites on the FM/TV splitter input cable, 10 in all.  The FM reception did not improve but the Over The Air UHF TV reception Quality improved noticeably.  My weakest TV station now has a stable Signal level and the Quality is pegged at 100%.  This is a nice surprise since it means that now all local TV stations on UHF will come in cleanly without dropouts and I can view all digital subchannels.  I was even able to rescan and added two more low-power stations never seen before. ?

LED lights

I have common LED lights hanging over a number of fish tanks and some grow lights over an indoor plant box and can hear this noise on upper shortwave and higher radio bands.  In a future article, I will explore RF noise from lights as its own special topic. For instance, why do some LED lights generate RFI and how to know before buying (I am using BR30 spot bulbs from name brands)?  Also, there is a new kind of LED “filament” light out now that uses much smaller LED’s on both sides of an aluminum strip, greatly reducing electromagnetic noise output (or do they??).  More questions than answers.

I will explore creating my own customized AC power cord attached to the AC power strips of the LED lights.  I will need to test this for safety and efficacy, so I will want to take some time to do this right.  The hope is that, using Jim’s info, I will be able to create a broad spectrum RFI suppression AC power cord and cost less than $30 each cord.  We’ll see.

Finally, I will look at “stacked” toroids using different mixes of ferrite Types, creating a custom RF suppression better than using just one Type of ferrite material, using AC cords as the main examples. For instance, the best set of graphs in Jim’s paper, in my opinion, are Figures 21 and 24 compared to each other.  Something I did not know before is that one can not only use multiple turns on a single toroid to get a lower, peaked frequency response, but also stack multiple toroids of the same Type to get a smoother frequency response.  Then on top of this, combine that set with other Types to create a customized frequency response curve.

Radios are quieter now.  Those pesky grow lights are still a problem as well as the upstairs neighbor’s lights which seem to be on a timer, making FM reception noisy again after 5pm!

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Dave says not all Jameco power supplies are linear and regulated

Note that not all power supplies are listed as "regulated linear"

Note that not all power supplies are listed as “regulated linear”

Many thanks to SWLing Post contributor, Dave Zantow (N9EWO), who replies to a post published yesterday regarding some of Jameco linear power supplies. Dave writes:

“A bit of a caveat on Jameco’s these so called Linear power supplies. This is based from my own experiences so is not fiction.

Bottom of this page : http://www.jameco.com/Jameco/catalogs/c151/P92.pdf

Over the years some of (but not all) these Jameco linear regulated power supplies are no longer clean for radio use.

Without changing the model number or description of the product, they have made changes with some (or much of ??) this “Linear Regulated” adapter line. Indeed they are still using a good old power transformer, but when it comes to the regulator part of the adapter, they have gone to switching type regulator device. So it produces a nice strong whine on a radio receiver just as a full fledged switching supply.

I had purchased a number of these so called linear supplies (sorry I no longer have the exact model number noted that I ordered) and experienced awful interference with any radio receiver. So I cracked open one of these to see what was up here and sure enough it was using a MC34063A inverting switching regulator .

Called Jameco and they flat out denied that they were using any switching devices in this Regulated LINEAR Jameco ReliaPro adapter. So I then sent a nasty gram email to the CEO of Jameco. I received an email back (was from the CEO too) and after some research they FINALLY did admit a change was made in some of the product line to use of a switching regulator . But he strongly made the point they would continue to still market these adapters as totally linear (yeah right ….nice guys).

I must add here that it does (or did not) NOT affect the entire line of these linear regulated adapters. About a year ago I ordered more (already had a few before) of the 12 volt 1 AMP model 170245 , and these are (or were anyway) totally clean and are excellent.

Also note that Jameco purchases up surplus “linear regulated” adapters from time to time. This 6 volt 500 ma one here is an example and is (or was anyway) nice clean one and uses no switching regulators. Our 2 tested samples of this adapter from about 5 years ago used a nice 7806 analog regulator. Perfect for use with many SW portables, (including the Sony ICF-SW7600GR with a plug change). But a warning again from experience , they are all subject to changes without any warning (and this one may have changed too for all we know ??)

They appear to stick the ReliaPro name as the manufacture on all adapters (if it was made by Jameco or not)

So Caveat Emptor.”

Duly noted, Dave! I’ve also noted that not all of the power supplies on their linear power supply page are listed as being a linear supply (see screen grab at top of page).

I may contact Jameco about this too and see if they can adjust their search results to properly reflect a selection of regulated linear supplies.

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How to replace a noisy wall power supply

JamecoWallPowerSupplyRegarding noisy switching power supplies, SWLing Post reader, Dan Lewis, comments:

“Google the following: “Jameco linear wall transformer”, and you’ll find a suitable non-switching replacement.

Jameco still has a number of linear transformers in their catalog at reasonable prices. I haven’t bought anything from them in many years but when I dealt with them frequently a number of years back they were always reputable.”

Many thanks for your suggestion, Dan! Jameco is a reliable company and I’ve also been a long-time customer. If you know how to pick the proper power supply for your radio (or any other electronic device) click here to view a list of regulated linear supplies on Jameco’s website. [Also note this follow-up post.]Otherwise, keep reading…

How to find a replacement AC adapter/power supply

When you purchase a replacement power supply, you must make sure that several properties match that of the device it will power, else you could cause damage.

There are four properties you need to match: voltage, rated current, polarity and tip size.

Voltage

Most consumer electronics are powered by and rated for 4.5, 5, 9, 12, or 13.8 volts DC. Of course, there are exceptions. It is important that you match the required voltage exactly. Most radios and electronic devices display their required voltage and voltage tolerance on the unit itself, on the supplied switching power supply, and/or in the owner’s manual.

Rated Current

Like voltage, rated current is usually displayed somewhere on the device, existing power supply or in the owner’s manual. Current is usually indicated in amps (A) or milliamps (mA). Unlike voltage, rated current on your power supply does not have to match the device exactly. You simply need to make sure the power supply meets or exceeds your radio’s required current.

For example, if your radio requires 800 mA (or .8 A) and you find a power supply rated for 500 mA, you should not use it. If you find a power supply rated for 2 amps (or 2000 mA), it exceeds the 800 mA rating, so you’re good to go!

Unlike voltage, your electronic device or radio will only draw the amount of current it needs from the power supply.

Polarity

Click here to read more about tip polarity. (Source: WikiPedia)

Click here to read more about tip polarity. (Source: WikiPedia)

You’ll need to determine if your radio requires a plug with a positive or negative tip (a.k.a. center conductor).

Fortunately, manufacturers have long used standard symbols to make polarity obvious (see image).

You’ll typically find a polarity symbol printed on the back of your radio, near the plug-in point, in the owner’s manual or on the back of the existing wall adapter.

Note: Be very careful matching polarity! Some radios and electronic devices are not properly protected against reverse polarity; damaged can occur immediately after supplying voltage with incorrect polarity.

TJamecoWallPowerSupplyip/plug size

You need to make sure that the inner diameter and outer diameter of a replacement wall adapter will match that of your existing adapter.

This can be the most difficult property to match.

Occasionally, radio manufacturers will actually specify the tip size in their owner’s manual, spec sheets, or on the product page of their website. I’ve even had luck calling manufacturers and asking a technician for the plug size.

ACAdapterTip

Specification sheets will typically indicate plug dimensions with an illustration.

Otherwise, you can always measure the existing power supply tip (both inner and outer dimensions) using calipers.

Once you have those dimensions, finding the appropriate replacement power supply is quite easy. Indeed, companies like Jameco provide specification sheets (click here for an example) that indicate dimensions for each power supply they sell.

Once you’ve matched the voltage, rated current, polarity and tip size, you can purchase a regulated linear power supply with confidence!

Keep in mind: there are most likely other devices in your home with noisy switching power supplies that could be causing radio interference. Check out my noise trouble shooting section of this article to help identify local sources of radio noise.

Update: check out this follow-up post regarding Jameco power supplies–not all are truly linear regulated.

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Sangean blames AM interference on power supply and government regulation

Sangean-AMFM-RadioAfter the Sangean WR-15 received low marks for AM reception in an Amazon review, Bob of Sangean America replied that poor reception is due to the radio’s switching power supply–a design that is federally mandated.

Many thanks to Jeff over at the Herculodge for posting this (click here to read the full response).

It’s a shame the WR-15 can’t accommodate internal batteries as battery operation this would solve the problem.

If I owned the WR-15, I would simply replace the switching type power supply with a regulated power supply.

Looking at the back of the WR-15 (below), it appears it requires 12 volts DC, 1.2 amps and an adapter with a positive center tip. Though I’m judging this only from the image, the plug looks to be a common size.WR-15-back I bet I have a power supply that would fit the bill in my junk drawer.

Bob, at Sangean America, claims moving the radio at least one foot from the power supply should help. In truth, I believe much of the noise may be conveyed by the power cord itself, though I may be wrong.

It’s a shame Sangean engineers couldn’t compensate somehow for the noisy power supply as it seems this radio was actually marketed to AM radio enthusiasts.

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