Chasing down interferance
 

I've been using my antique radios lately, and it had got to the point where AM was nearly unusable, due to buzzing and interferance.

I located the noise sources by shutting off one breaker at a time, until it went away. I ended up finding one grey market LED lamp, the treadmill, and the power supply to the Wii U. I also unplugged the computer. With all that done, reception is awesome now.

If you're struggling with am reception, keep trying, it is possible to get it back. I can get stations which have been lost in noise for years, and the sound is good now.

I need to go on such a hunt soon. Lately, something has been intermittently interfering with the agile modulators I use to transmit to my TVs.

It took less than an hour, I thought it would be really time consuming or difficult, but it was super easy, and the results are amazing. I had really written off using AM radio, and now it's back just like it was when I began this hobby.

It will be interesting to know what it is.

What does the interference look like?

I'm an AM DXer. I found that my CPAP would make noise running and a power brick for my son's laptop would make weird noises. Interference looks like lots of dashed lines in motion.

This seems like typical motor commutation interference.

Zenith had a device they called "the growler" for testing analog TV sync circuits. It was a metal box with RF input and output ports that contained a vacuum cleaner motor coupled to the signal. It had a two stage speed control circuit that cyclicly varied the speed of the motor and the rate of change of the speed, thus creating interference streaks that ran through all possible phases with respect to vertical and horizontal sync. Eventually, integrated analog sync circuits could sync up when the signal was so much smaller than the noise that you could not make out what the picture content was.

That's the second diagnostic tool use I've heard for the word "Growler" . In electric motor servicing there is a tool called the growler that will indicate shorted windings in a motor's armature . Since the electric motor servicing growler predates mass market TV , I believe the name of your device was borrowed from the original growler ...

A buddy of mine was fond of complaining about how bad the RF interference is in town. 75-40 meters was basically unusable and 20 was pretty rough too. We got a battery for the radio and starting flipping breakers. Turned out he was generating most of the noise! He had all sorts of stuff that was interfering. Got most of it dealt with but he still likes to complain about "the noise in town".

Very interesting; I always assumed the Zenith growler was named simply for the noise it made.

I once had an RFI problem that made SW listening unbearable. Located the problem at a street light with a bad sensor across the street. Got the city to change out the sensor and the problem went away!

Some stuff on armature growlers..

https://www.youtube.com/results?sear...mature+growler

:) Awesome ! Yes those are exactly what I remember . Somewhere in my collection of stuff I'll never use/get to there is one that I bought at a yard sale years ago .

When the ATSC high def digital over the air systems were tested, one of the tests was a vacuum cleaner motor that made RFI. To see how well the transmission methods handled it.

I was surprised to have interference on the FM band due to LED lamps. They aren't exactly TOTL R40 lamps. They're the Sunbeam badged from Dollar Tree. Two for a buck! This house has those can lights, popular in the early 2000's. The switch is on the other side of the wall from the radio.
The FM reception is great when the lights aren't on. :scratch2:

This kind of story is part of the reason I've been sticking with incandescent/halogen.

The AM reception on this radio in the same location is perfect with the same lights on. I thought it was the dimmer I had in that same location, when I was using incandescent R40's, so I put the switch back in.
The lights are on a lighting circuit, the radio is plugged into an appliance circuit.

I have a whole bunch of LED lamps which put out almost no interferance. I think if you stick with a quality brand, and make sure it's UL listed, then check it before buying lots you will be okay. It's great to have lights that don't get hot, or alternately are a lot brighter than previously possible in a given fixture.

:sigh:This is why I only use incandescent or T12 fluorescents in my shop. The portable drill battery pack charger made interference. I routinely install line filters (M-derived from junk SM power supplies) on the old radios I restore for others. It does make a difference and it is worthwhile adding grounded cords to all restorations.

Most times the noise is NOT on the power line (like AM buzz is from dimmer switches and faulty photocells) but more often noise is radiated at the lamp. The older the better and even the early compact fluorescent lamps with magnetic ballasts were not a problem if they were properly grounded.

But when the ballasts went electronic, it started. I found the T8 lamps on a 2-lamp ballast were only a minor problem but when the 3 and 4 lamp ballasts were used it became unbearable, commensurate with current. Many compact fluorescent lamps with twin, triple or quad tubes (not spiral lamps) had electronic ballasts. I designed lighting for retirement homes. I looked high and low for the least interfering fixtures, even if it meant not using the cheapest OR most efficient ballast.

I tested a bunch of LED lamps once and found the current waveform was very non-sinusoidal on almost all of them. Some generated much more AM and FM noise. The biggest surprise was the waveforms were all radically different. If doing a spectral analysis, a square wave by definition is comprised of harmonics.

FCC EMI limits are outdated, CFR 15 consumer is just a toothless standard. The switch mode power supply SMPS is here to stay, thanks to energy star and other forces to reduce overall consumption.:thumbsdn: