Tag Archives: QRM

How to replace a noisy wall power supply

Regarding 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)

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.

Tip/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.

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.

Sangean blames AM interference on power supply and government regulation

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After 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.

Video: How to fight radio noise in urban areas

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London Shortwave, a regular contributor to the SWLing Post, lives in London, England and copes with serious amounts of radio noise (QRM) at his home. Unlike many urban radio listeners, the QRM didn’t chase him away from the hobby, rather he looked at it as a challenge. Besides taking his radio kit outdoors to escape the noise, he also has a noise mitigation set-up at his home which has been refined over the years.

London Shortwave shared this video demonstration earlier this year on his YouTube channel. Here’s his description:

In this video I demonstrate an improvement to indoor radio reception quality, which is possible to achieve in an urban environment.

I compare using a Tecsun PL-390 portable receiver to a radio set-up that combines Lowe HF-150’s sync detector, the Wellbrook active loop antenna and real-time noise reduction software.

I recently told London Shortwave that he’s a QRM-fighting Samurai; I believe he certainly deserves the title!

Any other QRM Samurai’s out there?

Living in a National Radio Quiet Zone

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The Green Bank Telescope: An impressive parabolic dish covering 2.3 acres, the GBT has the largest collecting area of any fully-steerable telescope in the world. (Photo: R. Creager, NRAO/AUI/NSF)

Many thanks to SWLing Post reader, Paul, who shares this National Geographic video about Green Bank, West Virginia, USA–home of the National Radio Astronomy Observatory (NRAO):

My wife and I took a camping trip to Green Bank in the late 1990s when the massive Green Bank Telescope was about 80% complete. The NRAO site is inspiring and you (of course) will find no better place on the east coast for RF quiet conditions.

The staff at the NRAO give daily tours throughout the year–click here to view the schedule and costs.

I’m overdue for another visit.

WSJ: “FCC Agents Trace Radio Interference”

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Poorly engineered fluorescent ballasts are oftern culprits of broad spectrum radio interference. (Image: HowStuffWorks.com)

Poorly engineered fluorescent ballasts are often culprits of broad spectrum radio interference. (Image: HowStuffWorks.com)

I’m happy to see RFI being mentioned in the Wall Street Journal.

Many thanks to SWLing Post reader, Ulis, for the tip:

(Source: Wall Street Journal)

A federal agent who shows up unannounced at a building along a Texas highway might be looking for any number of things: illicit drugs or immigration violations, say, or illegal firearms.

Or fluorescent lights.

Which was what the agent had in mind who walked into the Perfect Cuts salon in San Antonio last July. The lights were violating communications regulations.

The agent had used signal-tracking equipment to home in on the offenders and told the owner, Ronald Bethany, that his lights emitted radio signals that interfered with an AT&T cellphone tower.

[…]The mixed signals aren’t always so weighty. In recent years, the FCC has issued warning letters directing people to stop operating cordless phones, television sets and wireless cameras.

[…]The FCC can demand fines up to $16,000 a day or $112,500 an incident from people who aren’t FCC licensees. Offenders usually rectify problems, the FCC says, often working them out with whomever is complaining.

Managing the radio spectrum “has been part of our core mission since the inception of the FCC in 1934,” says Julius Knapp, head of the agency’s Office of Engineering and Technology.

[…]The government doesn’t much care why interference happens. To the FCC, noise is noise.

In a 2013 letter, the FCC wrote to the owner of a plasma TV set after a ham-radio operator complained to the agency of interference. “Continued operation of the television,” warned the letter, from which the TV owner’s identification is redacted, “is not legal under FCC rules.”

[…]Ham-radio operators are a frequent source of complaints. A 2012 FCC letter told a Pomona Park, Fla., resident to stop using a well pump that conflicted with amateur-radio frequencies.

[…]Radio hobbyist Tom Thompson of Boulder, Colo., last year tracked a signal using a homemade contraption. After knocking on the suspect’s door, he traced it to ballasts on marijuana grow-room lights. He says he built a filter that the grower agreed to use.

Ballasts are frequent offenders. Makers of the components, which regulate electricity to bulbs, test them for FCC compliance. Some interfere anyway.[…]

Read the full article on the Wall Street Journal online.

Document radio interference via the Ofcom Spectrum Management Survey

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PLT devices can produce broad spectrum noise on the shortwave/amateur radio HF bands

Nige (G7CNF) recently contacted me regarding a survey he has created to help document and fight radio interference from power line technology and other sources.

If you live in the UK and can create an Ofcom case reference number, please consider contributing.

Nige writes:

I have created a new forum (or rather relaunched my old one but with some rebranding) […] dedicated to discussing and curing [radio] interference.

I was contacted recently on one of my PLT YT videos by a SWL who was suffering PLT interference and it reminded me that since 2010, SWLs have had no ‘right to complain’ in the UK after Ofcom delegated domestic broadcast interference to the BBC. Frankly I think that is unacceptable and I want to address that imbalance.

I have created a new survey, the ‘Ofcom Spectrum Management Survey.’ Unlike the previous incarnation which was aimed at radio amateurs alone, this time I have opened it up to all radio users, regardless of type; the only qualification needed to fill this survey is an Ofcom case reference number. […]

Like the RSGB noise floor monitoring campaign which has just been stepped up to incorporate the use of the Cross-Country-Wireless Sentinel SDR noise monitor, I believe that my Ofcom survey will offer insights into the regulator’s performance over over time – and highlight its deficiencies by placing Ofcom spectrum abuse cases in the public domain.

The survey can be found here:
http://interference.org.uk/survey/index.php/955793

The forum, here:
http://interference.org.uk

Many thanks for your time and the best of luck with the hobby.

Nige.G7CNF
http://interference.org.uk

Nige, thank you for organizing this survey and campaign–best of luck moving forward!

Ajit Pai is trying to save AM radio “before it’s lost in the static”

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Many thanks to Andrea Borgnino for pointing out this article in today’s New York Times regarding one man’s quest to save AM radio from impending noise (QRM):

The digital age is killing AM radio, an American institution that brought the nation fireside chats, Casey Kasem’s Top 40 and scratchy broadcasts of the World Series. Long surpassed by FM and more recently cast aside by satellite radio and Pandora, AM is now under siege from a new threat: rising interference from smartphones and consumer electronics that reduce many AM stations to little more than static. Its audience has sunk to historical lows.

But at least one man in Washington is tuning in.

Ajit Pai, the lone Republican on the Federal Communications Commission, is on a personal if quixotic quest to save AM. After a little more than a year in the job, he is urging the F.C.C. to undertake an overhaul of AM radio, which he calls “the audible core of our national culture.” He sees AM — largely the realm of local news, sports, conservative talk and religious broadcasters — as vital in emergencies and in rural areas.

“AM radio is localism, it is community,” Mr. Pai, 40, said in an interview.”[…]

Continue reading the full article on the New York Times website.