radio

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150225-1017 EST

enireh:

Use a logical troubleshooting procedure.

It would be useful to have both a cord powered and battery powered radio for testing. This provides an easy means to determine if the interference is primarily conducted or radiated noise.

If a battery powered radio does not experience as much noise as a cord connected radio, then you are looking for conducted noise. Standard magnetic ballast fluorescents are a major source of conducted radio noise. A standard low pass filter installed inside the fixture, such as a Corcom 5VR1, will greatly reduce conducted noise and some radiated noise.

Tune your radio to a frequency between 550 and 700 kHz where there is no station, or at least a weak one. Turn almost everything in your house off. Leave clocks based on line frequency on, too much trouble to reset. Determine the base noise level. One at a time turn on circuits or loads and listen for an increase in noise. Turn off and try another. This should allow you to identify sources.

Some sources may be broad spectrum, and others narrow. For example my new LED 4 ft light shows noise at about 680 kHz, and some other frequencies that don't seem to correlate. I will comment more later.

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150225-1130 EST

There are many stations in the low part of the AM band that make it hard to spot the harmonics from the LED fixture. Looking further I found good signals at 1120 and 1040. The difference is 80 kH. This means I should see signals at 560, 640, 720, 800, 880, 960, 1040, and 1120. Other than 640 most of the other frequencies are on a strong radio station or close. Now it appears my original 680 should be 640. This means the oscillator in the LED ficture is about 80 kHz, and somewhat spread in its spectrum to reduce AM radio interference.

What can you expect from a dimmer? It should have 120 Hz fundamental with some low pass filtering at the input, thus in the AM band fairly uniform noise across the whole band. This is going to be a difficult noise signal to minimize.

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150225-1331 EST

I finally got my multi-band receiver to run on battery. A large amount of the dimmer noise is from RF radiated energy.

My simple suggestion is that if one or more dimmers are your problem, then either don't listen to AM when the dimmers are in use, or turn the dimmers off when you want to listen to the radio.

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