Category Archives: QRM

Taming the Noise: Don Moore’s Simple, Cheap Filter Solution for Traveling DXers

Many thanks to SWLing Post contributor Don Moore–noted author, traveler, and DXer–who shares the following post:

A Cheap and Simple Noise Filter

By Don Moore

Don’s traveling DX stories can be found in his book Tales of a Vagabond DXer [SWLing Post affiliate link]. If you’ve already read his book and enjoyed it, do Don a favor and leave a review on Amazon.

My DXing career started over fifty years ago in an upstairs bedroom in tiny Milesburg, Pennsylvania. I had a consumer-grade multi-band radio and some copper wire strung from the roof to a nearby tree. It was a simple setup but it worked very well. Do you know what I didn’t have? A noise problem. The only time I remember noise ruining my DX was when my mother was using the electric mixer and that meant she was making cookies or a cake. I never complained.

Times have changed, haven’t they? What DXer doesn’t complain about noise these days? I know people who have left the hobby because the place they lived at and DXed at for decades gradually became so noisy they couldn’t DX anymore.

Unsurprisingly, a lot has been written about how to find and eliminate noise in your home. However, most of my DXing is done as I wander the globe. I try to find places to stay at that should be good for DXing. But no matter how good a place looks beforehand, there’s no way of knowing what the noise level will be until I get there.

As a traveling DXer, I need quick, easy, and compact noise solutions. The best solution I’ve found are these CCTV distortion filters (ground loop isolators) that Brett Saylor recommended to me several years ago.

No, these weren’t designed for radio use. And they aren’t a miracle solution that will eliminate all the noise that plagues DXers. Sometimes they’re no use at all. But I’ve DXed in dozens of locations over the past ten years and there have been multiple occasions where one of these filters has turned what would have been a disappointing stay into a good DX session. I don’t go anywhere without two of these packed in my mobile DX shack.

But let me show you some results. All of these SDR screenshots were made with SDR-Console using an Airspy HF+ Discovery SDR connected to a PA0RDT mini-whip antenna.

I spent last summer in the north suburbs of Chicago and several times went to a park to test my DX equipment. Around midday, the lower shortwave frequencies were filled with noise peaks. On this first image, it’s hard to pick out WWV on 5 MHz from all the noise peaks. In the second image the filter hasn’t totally eliminated the noise, but WWV’s signal is now strong and clear.

The noise was nearly as strong on 49 meters but the filter almost totally eliminated it. CFRX’s signal on 6070 kHz was slightly weaker with the filter, but it was significantly more listenable without the noise.

Which frequencies noise affects can vary between locations. At that park the noise was gone above about 11 MHz. While traveling across the US in mid-October, I stopped at a park just west of Kansas City to do some more DXing and equipment tests. The noise there was bad in the middle shortwave bands, such as in the 25 meter band.

But the filter did a good job cleaning it up.

Finally, about two years ago when I was DXing in Rafina, Greece, the noise was bad on the higher bands. Here are before and after screen shots on the 16-meter band.

These filters should work with any coax-fed antenna. I’ve used them with beverages, Wellbrook loops, the PA0RDT, and the MLA-30+ loop. If the antenna has an interface, such as the last three mentioned, the filter goes between the interface and your receiver (and not between the interface and the antenna). I’m not sure what the impedance on these is, but I’ve used them with both 50- and 75-ohm coax cable.

Sources of the Filters

An Internet search for “CCTV Ground Loop Isolator” brings up all kinds of products. They are probably all the same but I have no way of knowing that. So I recommend getting the exact ones that I have purchased. Just compare the product to the pictures of mine.

Here are links to three current sources for these exact ones on Amazon. They can also be found on eBay and other sites. [Note that all of these links are affilliate links that support the SWLing Post at no cost to you.]

A Few More Ideas

At just a couple dollars each, every DXer should have a few of these filters in their shack. But types of noise vary and at several places I’ve DXed from using one of these filters made no difference at all. When that happens I have a few other solutions to try.

The first thing I try is to either move the antenna or, if it’s directional, to point it in a different direction. On several occasions that’s all it has taken to totally eliminate what at first seemed like an impossible noise problem.

If the noise is coming in through the power lines, unplugging the laptop and DXing off of battery power might do it. (I only use SDRs powered off the USB connections on my laptop.) If you do that, be sure to unplug the cord from the outlet and move it away from the wall. If you unplug the cord from the laptop and leave the other end plugged into the outlet, it may act as an antenna and radiate the noise from the power lines into your SDR. And, yes, I learned that lesson the hard way!

Do you have any interesting experiences or solutions to the DX noise problem? Please leave them in the comments section.

Radio World: John Kean Examines Modern AM Interference Challenges

Noise-Reduction Ideas via Hackaday & Electronics Unmessed

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Many thanks to SWLing Post contributor Dennis Dura for sharing this excellent Hackaday feature: Quieting That Radio. If you’ve ever struggled to hear weak signals through modern RFI, this piece, featuring content from Electronics Unmessed, is well worth checking out. It explores the hidden interference SDR setups often face and offers simple, practical/inexpensive fixes—like adding a counterpoise or ferrite choke—that can make all the difference in pulling in those hard-to-hear stations. This is advice we’ve recommended in past articles, but it’s brilliant to see demonstrated improvement.

Click here to read on Hackaday.

Radio World: NRSC Studies RF Noise on Various Roadway Types

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Many thanks to SWLing Post contributor, Dennis Dure, who shares the following item from Radio World:

NRSC Studies RF Noise on Various Roadway Types (Radio World)

Radio World asked Cris Alexander to read the report and comment

The National Radio Systems Committee recently published the results of a study on AM band noise.

The report, principally authored by John Kean, is titled NRSC-R102, “Measurement of AM Band RF Noise Levels and Station Signal Attenuation.” It was released in January.

The study consisted of several measurement series conducted along roadways both in urban and rural areas, measuring the signal strength of three different Baltimore/Washington 50 kW AM stations as well as the RF noise on three different unoccupied AM band frequencies.

Measurements were made across five environments: rural, rural-suburban, suburban, urban and dense urban. The results were mostly as one would expect, but there were a few surprises. [Continue reading…]

Click here to download the NRSC PDF report.

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 (19 Dec 2024): ELISYS now sells Kostas’ NR-1 noise blanker and ships worldwide. Check it out by clicking here.

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.

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 →

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 →