Radios and fluorescents--Noise

[Dennis Alwon]

I have had a number of people ask me what can be done with an electronic fluorescent ballast to stop it from interfering with radio broadcasts. Any help?

 

[480sparky]

Tell them to stop broadcasting.

Seriously.... try just moving the radio somewhere else. Unfortunately, there's a labal on the back or bottom of the radio (something about Part 15 and all that) that basically states, in FCC legaleze, 'tough cookies'.

 

[Cow]

I thought RF interference only occured with lower end ballasts? The kind of lights homeowners buy from HD and Lowes....

My figuring was that you never hear about RF interference in commercial office buildings, schools, etc where the contractor supplied the lights and the fact there are a lot more of them.

 

[gar]

081229-2044 EST

Dennis:

You can greatly reduce this noise with a low pass filter in the fixture and close to the input leads to the ballast.

See Corcom now part of Tyco. These typically include capacitors between the power lines and from the power lines to ground (EGC). The ones with greater attenuation have series line inductors, and the capacitors on both sides of the inductors.

See
http://www.cor.com/Series/RFI.asp
http://www.cor.com/Series/PowerLine/FL/
http://www.cor.com/Series/PowerLine/DK/

.

 

[Dennis Alwon]

Thanks Gar... I figured there had to be some filter for this.

I thought RF interference only occured with lower end ballasts? The kind of lights homeowners buy from HD and Lowes....

Could be but I believe the last person that mentioned it had an EC buy them at the local electrical supplier. Apparently they worked fine for 3 years, in this case, and now he is having a problem. I suggesting disconnecting lights to see which one is causing the problem.

 

[gar]

081229-2131 EST

Dennis:

I did not catch the electronic modifier of ballast on first reading. However, the RFI your are experiencing, whether from an electronic or standard ballast, is probably mostly from the arc in the lamp. A low pass filter in the line only reduces the noise getting back on the branch circuit wiring. By reducing the noise getting to the branch circuit there is less conducted to a plugin radio, and less radiated from the branch wiring.

There is still direct radiation of RF energy from the tube itself. In the case of an 8 foot lamp that is a long antenna.

I have many 8 footers in my house and when the house was built I installed a line filter in each fixture. This greatly reduced RFI noise.

Electronic ballasts excite the lamp with about 30 kHz which puts them above the audio range and below most radio channels. I believe there are still weather channels below 550 kHz. I would expect there are substantial harmonics from the 30 kHz excitation. I have never bother to make any measurements on this potential problem.

Generally I only listen to AM radio in the car. I listen to a strong station at 760 kHz and do not get much interference except at some localized locations --- some power lines, some cable TV lines, and outside my son's shop there is noise from the computers and CNC machines.

I have not looked into the design of any modern radios, but my guess is that the majority do not include any tuned RF stages before the first mixer. Thus, without tuned RF stages the radio is much more susceptible to broadband noise. Back in the tube days car radios had one tuned RF stage before the tuned mixer. Higher quality home radios had the same arrangement. A 1928 radio I have I believe has two tuned RF stages before the mixer, and the If frequency was lower than the more recent 455 KC (kHz) value. It used to be called kilocycles. The two input stages would have helped to reduce image interferrence.

.

 

[ghostbuster]

To add to Gar's comments:

We have measured these radiated higher harmonics of 30khz. as high as 200 khz.They have caused radiated interference problems with patient monitoring systems and commercial parking lot gate monitoring systems.