RAN Technology

Beware of the LED Noisemaker!

Technical 0 Comments 01/02/2021 

MR-16 lamps have no home in the hamshack!

Posted By: Robert Nickels (ranickels)

Halogen type MR-16 lamps are commonly used in track lights and other spot lighting applications so what would be cooler than to drop in LED replacements!   

A lot, as it turns out.   The LED replacements are HORRIBLE RFI emitters that totally trashed several ham bands when I unknowingly installed them.

Halogen spot lights are 12 volt devices so it's long been common practice to supply switch mode power supplies with them rather than heavy transformers.   Fine, as far a it goes but those SMPS supplies are notorious RFI/EMI emitters and the once that came with my IKEA tracklights went in the garbage the first time I tried it.   Having things like 12 volt transformers on hand I just ran the lamps on 12 VAC and all was well - until the "upgrade to LED".

I have to say I thought it was great to be able to buy plug-in LED replacments at an affordable price.  I tried one and it worked from my AC supply and I liked the light so I bought a handful more.   All seemed well until I noticed a terribly strong blanket of broadband noise that completely wiped out the 75 meter band - only the strongest signals could be heard above the solid S9 noise level.  The SDR said it was at least 30-40 dB higher than normal.

The problem is the MR-16 replacement LEDs are designed to provide that convenient plug-in compatibility with existing 12 volt lighting systems.  That means that however many LEDs are needed internally - connected in series and parallel to get the desired output and color - they must run from a 12 volt source.  That means each MR-16 LED lamp has a little switch mode power supply inside!   And they put a high amount of RF on the 12 volt line which is then re-radiated by the wiring just like a little transmitter!    In fact, when multiple LEDs are used in the same lighting fixture their noise patterns combine and overlap to make the noise even worse.    On the bench I measured several volts of RF superimposed on the 12 volt DC supply wires, and no combination of filter capacitors or CLC filter networks would reduce it to any kind of tolerable level.  The noise was actually tunable with the supply voltage, varying from around 1.5 to 5 MHz as the supply varied from 8 to 15 volts.   Some combinations of filter capacitors actually increased the noise level as if a resonance was occurring!     It didn't take long to determine that the RF emissions from these LEDs would not be easily mitigated with typical measures and even so, the combined effect of multiple LEDs strung together with wires to re-radiated the conducted emissions was not predictable.

I purchased the FEIT brand and can't speak for other types, but they all probably use the same ICs and reference designs as the Maxim (below) so I'd expect the same results.    I could not find a readable part number on the 10-pin SMPS controller IC in the lamp I autopsied, but again the functionality is going to be the same - a current sensing buck converter.

The spectrum analyzer plot confirms these MR-16 LEDs have no place in the ham shack!   I have used LED "shop lights" which string lots of LEDs together and operate them directly from the AC main and since this type doesn't need to have the buck converter they are likely going to be much cleaner RFI-wise.


Click on the image title or on the image itself to open the full-sized image in a separate window.

   Lakeshore Industries of Manitowoc WI was an early follower of Wes Schum and Central Electronics to supply single sideband transmitters to early adopters of the new mode in the mid-1950s.   Both companies used the phasing method developed by Don Norgaard at General Electric and made popular through articles in QST, CQ, and GE Ham News.  Like most companies, Lakeshore sought to c...  READ MORE
- Robert Nickels (ranickels),  02/26/2021 

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I have always been intrigued by the International Crystal CB radios which had a unique appearance with a channel selector that resembled a telephone dial.    The high end "Executive" models were big and expensive and sported an aluminum trim ring that no other radio had.    So I had to buy one to play with.     It was cheap, like $25 and ...  READ MORE
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- Robert Nickels (ranickels),  02/11/2021 
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Plymouth Indiana might not be famous for too many things, but John Meck Industries was the first manufacturer to start producing radios for home us in the US after World War II.   He'd started the namesake company prior to the war but like most others in the radio business it was converted to wartime production, making quartz crystals among other things.   Later, thousands ...  READ MORE
- Robert Nickels (ranickels),  01/30/2021 
   If, like me, you enjoy flipping through old issues of 73 magazine from the 60s, you're bound to have at least seen the ads for the Transcom SBT-3 three-band SSB tranceiver.  Being made in Escondido CA in the mid-60s, my guess has always been that engineers from other San Diego SSB compnanies such as Don Stoner, Les Earnshaw from Southcom, Herb Johnson, founder of Swan or Faust Gonsett may...  READ MORE
- Robert Nickels (ranickels),  01/16/2021 


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This short article about the AWA Forestphone was the last one put on the Midwest Classic Radio Net website by for former webmaster George K9GDT before he unfortunately became a Silent Key.  MCRN articleNow that a longer version has been published in Electric Radio magazine I thought I'd include it here as well.Throughout most of the 20th century AWA was Australia's leading electr...  READ MORE
- Robert Nickels (ranickels),  01/13/2021 
   Alexander M. Lewyt died in 1988 at the age of 79, a holder of patents on scores of inventions. His penchant for invention, he once said, was so strong that he had chronic insomnia from lying awake at night envisioning new products. When he learned of undertakers’ difficulty in fastening neckties on corpses, the teen-age Lewyt devised a new kind of bow tie that clipped on. He sold 50,000 of t...  READ MORE
- Robert Nickels (ranickels),  01/08/2021 

AN/GRC-9 Bias Battery replacement

Cheap and easy fix using coin cells
Category: Technical
The Korean-war vintage AN/GRC-9 is one of the most useful and fun military field radios for ham use, as with AM and CW modes and 2-12 MHz coverage and a VFO it's all ready to go on several ham bands.    The battery tube superhet receiver is also power-friendly and sensitive and stable enough to copy CW and SSB but has one annoying flaw - the 4 volt bias battery used by the audio...  READ MORE
- Robert Nickels (ranickels),  01/03/2021 

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