Category Archives: QRM

Kostas presents the NR-1 Noise Blanker!

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Many thanks to SWLing Post contributor, Kostas (SV3ORA), for sharing the following post which originally appeared on his website:

Update June 1, 2024: Kostas is not currently selling the NR-1 as a product but has, instead, made the entire project open and available for everyone to build their own. You may contact him for more information.

The NR-1, a revolutionary noise blanker that works directly on the antenna!

I designed my own noise blanker because:

    • I was tired of that HF noise that could not be beaten otherwise.
    • I wanted to remove it before it gets into my transceiver.
    • I could not install a separate “noise” antenna/coaxial for diversity.
    • I wanted to remove noise interference from any direction.

NR-1 is a revolutionary Noise Blanker which is the result of two-years of development and extensive testing by Kostas sv3ora.

NR-1 works directly at the antenna. This has significant advantages over the classic noise blankers which work at the intermediate stages of the receivers. It does not require a second “noise” antenna for its operation.

Furthermore, it is not based on cutting-off of amplifiers, unlike common noise blankers
do.

Because of these, the NR-1 is superior, compared tocommon internal Noise blankers of radios:

    • NR-1 removes noise before it even reaches the receiver. Thus, the front-end RF
      stages of the receiver are unaffected by noise, unlike a common noise blanker
      which removes the noise after it has first passed through the internal circuits
      of the receiver.
    • NR-1 removes high-level, high-repetition-rate noises that common noise blankers
      usually cannot cope with.
    • NR-1 is not affected by strong near-by signals. Instead, common noise blankers
      perform poorly when there are strong near-by signals and they distort the signal of the station we want to listen.
    • NR-1 can be used by many radios. Because it is an external device, it can be
      connected to various radios/receivers without the need to modify them.
    • NR-1 has a built-in 8-band preselector and helps eliminate intermodulation (birdies)
      caused by strong local medium and shortwave stations, on RF direct sampling
      radios (eg IC-7300). The preselector is relatively wideband and does not affect
      the sensitivity or the waterfall spectrum in the amateur radio bands.
    • NR-1 has built-in variable gain preamplifier and variable attenuator. Preamplification is
      particularly useful in the high frequency bands, where some radios have limited
      sensitivity. Variable attenuation helps to reduce band noise for more
      comfortable listening to mid/high strength stations.

Comparison of the NR-1 with other noise removal systems (eg. QRM eliminator, X-phase etc):

    • NR-1 does not require a second (noise) antenna/coaxial-line to operate. Unlike QRM
      eliminators, NR-1 does not require an additional “noise” antenna and
      therefore no second coaxial cable out of the shack. The main transmit and
      receive antenna you are already using is sufficient.
    • NR-1 is easy to set up. In contrast, QRM eliminators require systematic testing of
      various noise antennas in different locations to perform satisfactorily.
    • NR-1 removes noise from every direction simultaneously. In contrast, QRM
      eliminators, depending on the noise antenna setup and their configuration,
      remove noise from one direction only each time. If the noise originates or
      “travels” through cables and reaches the antenna from different
      directions, QRM eliminators do not perform well.
    • NR-1 removes more than one noise source simultaneously because its principle of
      operation is not related to the phase of the noise.
    • NR-1 does not require constant adjustment. Once set for one band, it usually does not need to be reset. In contrast, QRM eliminators require resetting every few tens of KHz or so.

Kostas has documented all the details of the NR-1 for his own future reference in his page.

He has also created some YOUTUBE videos as demonstrations of the operation and the effectiveness of this antenna noise blanker.

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Frans experiments with the MFJ-1026 Noise Canceling Signal Enhancer

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Many thanks to SWLing Post contributor, Frans Goddijn, who writes:

“Last week I purchased the MFJ-1026 ‘noise canceling signal enhancer’ and I posted two blogs with video about it. Initially the device seemed as useless as it is good looking but then I found a configuration where the device is not only pleasant to have but also useful for radio listening.”

Here are Frans’ reports which he kindly shares from these two posts originally published on his blog, Kostverlorenvaart:

Part 1: MFJ-1026 deluxe noise canceling signal enhancer

Using a GRAHN antenna, (a VENHORST wire antenna for noise reference), the iCOM R8600 radio and optional bhi DSP audio noise canceling, trying to see what’s the best way to cancel noise — on the antenna entry point of the radio or at the speaker output end.

In this case the MFJ-1026 seems ineffective. The DSP at the audio output end works well and easy.

I have also tried two GRAHN antennas on the MFJ-1026, one for MAIN and one for AUX but that was also not noticeably effective yet.

I will also try the little whip antenna that MFJ supplied with the box. Further tweaking may turn out to be helpful on some other frequencies / signals.

Before installing the MFJ i used the little TECSUN H-501x to scan the room for any devices producing radio noise. It turned out that the two Apple Homepods sit in a dense cloud of radio noise, the Macbook Pro also radiates noise, EVE smart plugs controlling lights also produce radio noise, two little label printers s well and the HP printer/scanner too. So I moved those to the other end of the toom or to another room. Continue reading →

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Radio Waves: BBC License Fee Frozen, Battling RFI, Warning to RTL-SDR Users in Ukraine, and WRD Special Broadcast

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Radio Waves:  Stories Making Waves in the World of Radio

Because I keep my ear to the waves, as well as receive many tips from others who do the same, I find myself privy to radio-related stories that might interest SWLing Post readers.  To that end: Welcome to the SWLing Post’s Radio Waves, a collection of links to interesting stories making waves in the world of radio. Enjoy!

BBC’s funding system under fire (Marketplace)

In the United Kingdom, you need a license to drive a car, fly a plane, practice medicine and watch TV.

The “TV license” is what Brits call their system for funding their world-famous broadcaster, the BBC. Currently, it costs the equivalent of $216 a year and is compulsory. Anyone in the U.K. caught watching or recording programs broadcast on any television channel or livestreamed on an online platform without a license is likely to be prosecuted.

The BBC — the Beeb, as it’s known — derives around $5 billion a year from this source. That’s 75% of the total revenue it needs to run a vast media empire, comprising 10 national TV channels and 10 national and 40 local radio stations as well as its World Service broadcasts and a global news website.

Full disclosure: The Beeb is a content partner for Marketplace.

But the license fee is under attack. The government just announced that it’s freezing the fee at the current level for two years and not increasing it in line with inflation — a decision that could cost the corporation nearly $400 million. The government has also hinted that it would like to eventually scrap the license fee altogether. [Continue reading at Marketplace…]

RF Interference (Nuts and Volts)

It’s everywhere! It’s everywhere! Fortunately, you can take a bite out of RFI.

RF interference — is it interference to you? Is it interference by you? Possibly both! What does this interference consist of? And how can you tell what type is present? A topic that starts off with so many questions is bound to cover a lot of ground, so let’s get started. Continue reading →

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Radio Waves: Broadcast v Ham Radio, Marjorie Stetson’s Secret Wartime Work, Czech Republic MW Switch-Off, and PV RFI

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Radio Waves:  Stories Making Waves in the World of Radio

Because I keep my ear to the waves, as well as receive many tips from others who do the same, I find myself privy to radio-related stories that might interest SWLing Post readers.  To that end: Welcome to the SWLing Post’s Radio Waves, a collection of links to interesting stories making waves in the world of radio. Enjoy!

Alike, but Not Alike: Broadcast vs. Ham Radio (Radio World)

Experience in amateur radio can be a boon to the radio engineer

Starting in the 1920s and through the ’60s, almost every broadcast engineer was a licensed amateur radio operator. That has changed a bit, but the importance of being a ham has not.

Both environments involve getting an RF signal from Point A to Point B. But it is interesting to note that radio broadcast and amateur radio are similar and yet so different.

For those who don’t know much about ham radio, I’ll tell you that communicating locally or internationally, via licensed amateur radio, can be a fascinating and challenging hobby. There are about 700,000 hams in the U.S. and an equal number worldwide.

Physics

Broadcast and amateur radio operate under the same laws of science. Transmitters, transmission lines, antennas and receivers make up an RF path to convey a message.

Broadcast engineers know that signal propagation on AM and FM bands is dramatically different. It is because our FM band is roughly 100 times the frequency and 1/100th the RF wavelength of that on the AM band. Engineers also know that 950 MHz STL signals are line-of-sight and roughly a 10-times jump in frequency from FM broadcast frequencies. Each band has its own challenges in getting a useable signal through. [Continue reading…]

A Canadian opens up about her secret wartime work — eavesdropping on Japan (CBC)

Retired sergeant remembers what it was like on the ‘front line of the radio war’

At age 97, Marjorie Stetson has never told anyone her secret code number — until now.

That’s the identity code — 225 — that she typed on every page of her highly classified work for the Canadian Armed Forces during the Second World War.

The retired sergeant’s wartime work was so covert, she said, she had to sign 15 separate copies of Canada’s Official Secrets Act.

“Nobody knew where I worked,” Stetson told CBC News from her home in Massachusetts ahead of Remembrance Day. “Nobody knew what we did. Even my parents never knew what I did in the service.”

Her husband, an American sailor she met at a celebration marking the end of the war, passed away a decade ago. She never told him what she really did during the war.

Today, Stetson herself is only now learning about the true scope of her role and the significance of all those sheets of white paper she filled with encrypted messages from Japan. [Continue reading…]

Czech Republic: MW Switch-Off by 2021 (Radio Reporter)

Czech public radio ‘?eský Rozhlas‘ is stepping up its information campaign for listeners receiving mediumwave programmes, ahead of the planned switch-off of transmitters by the end of 2021. Since 1 November, more announcements have been broadcast to warn users and a call centre has been set up to explain the possible listening alternatives (from FM to DAB). In the run-up to Christmas, public radio will launch an intensive advertising campaign in the print media and online magazines on 22 November to promote the purchase of digital DAB receivers to replace analogue radio. [Continue reading…]

The impact of photovoltaics (Southgate ARC)

Seamus Ei8EP reports on the IARU Region 1 website that the 358 page Final Report on the Study on the evaluation of the Electromagnetic Compatibility Directive has now been published.

It is publicly available, free of charge, from the Publications Office of the European Union. The Political Relations Committee of the IARU Region 1 responded recently to a European Commission Roadmap on the environmental impact of photovoltaics.

The radio spectrum is an important finite natural resource which must be protected. While PV technology of itself is to be welcomed, the IARU submission pointed out the inherent problems of non-compliant installations, particularly the installation or retro-fitting of optimisers which can produce significant spectrum pollution for very limited efficiency increase.

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Guest Post: Indoor Noise and Ferrites, Part1

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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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Jack finds that chokes have a huge impact on switching power supply noise

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These “Wall Wart” type adapters can create a lot of RFI

Many thanks to SWLing Post contributor, Jack Dully, who writes:

I was putting some things in my radio junk parts box and came across some chokes. So I tried a test with my Tecsun PL-880 on battery and the Tecsun supplied switching AC adapter, with and without chokes on the adapter.

WOW!

I tuned to a vacant station on battery power with headphones on. Then on AC power, the hash and static were incredible. Putting one large choke on the adapter power cord, wrapped about four times and it decreased considerably. So I attached a second choke and once again the static & hash decreased even more, almost to the point of sounding like I was running just on battery power.

Those chokes really do work well.

Thank you for sharing this, Jack. I almost never operate my portables while connected to a power supply, so I often forget about the importance of using a choke with inexpensive, lightweight radio power supplies. Thing is, so many things in our houses and shacks are powered by these QRM generators. In the shack, I’ve added chokes I’ve picked up at hamfests to a number of various power supplies. It does certainly help decrease the noise level. I’ve even used them on power cords for other appliances in the house that tend to spew RFI.

If you ever find a deal on chokes at a hamfest or electronics store, grab some. They can be an affordable solution for those noisy power supplies we still rely on.

Thank you for the reminder and  tip, Jack!

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Lemons into Lemonade: Nick is taking advantage of Texas power outage to play radio

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Many thanks to SWLing Post contributor, Nick Booras, who writes:

I am stuck in the house in Texas, bored and with no power. So I decided to make a couple videos with my phone. One nice thing about a power outage… no RFI [Radio Frequency Interference].

This Icom 705 is an awesome radio! Perhaps your viewers might like these.

https://youtu.be/NeqwTyI1Az4

Thank you for sharing these, Nick! Yes, as we’ve noted before, power outages are an ideal time to play radio and indulge in a low-noise environment! And I agree with you: the IC-705 is a superb shortwave broadcast receiver.

I hope our readers in Texas will have power restored soon–this has been a rough week for many.

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