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#199186 - 02/15/11 07:41 PM Radio Interference and T8 Fluorescents Fixtures
twh Offline
Member

Registered: 03/11/04
Posts: 898
Loc: Regina, Sask.
I have a radio interference problem in a house. The problem appears only on the FM channels and there are two similar radios with the same problem. They are in different parts of the house and on different circuits. The problem is with fluorescent lights, only.

In the attached garage there are 6 x 4 foot, 4 lamp T8 fixtures. They have Sylvania Osram ballasts. They are on two switches and it doesn't matter which switch is on.

In the kitchen, there are 2 x 4 foot, 1 lamp T8 fixtures on one switch.

The house is about 3 years old and the problem has been there for the whole time, winter and summer.

The grounding is a ground plate and the system is properly bonded. All line, neutral and ground connections are tight.

I tried a .1 mfd capacitor in a garage fixture and in the panel, in all possible configurations (L-N, N-G, L-G, L1-L2) with no improvement.

With the radio outside and plugged it into an outside plug, the problem was still there, but the FM signal was weak. It is probably weak in the house, too, but it's bad outside.

I plugged the radio into a 100 foot cord and there might have been some improvement. Then, I plugged the 100 foot cord into the neighbor's house and the problem was gone. Both houses are fed from the same pole.

The neighbor has fluorescent fixtures that don't interfere with my customer's radio - a different make of ballast, though.

My conclusion is that the problem is in the wires, but now I'm out of ideas. The house is an hour away, so I can't go back unless I have a solution.

What did I miss?

Is there a filter I install on the panel?

Is there a filter I can plug the radios into?

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#199188 - 02/15/11 08:07 PM Re: Radio Interference and T8 Fluorescents Fixtures [Re: twh]
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
twh;

Most likely the Interference is generated from loose Pin Terminations.

Verify the Lamps' Pins are secure in the Lamp Holders.

With the Radio and Lamps on, rotate the Lamps in their Holders. Check for varying Interference.

Additionally, check for loose lead wires to the Lamp Holders.

Ballast RFI would affect the AM Spectrum more than FM, whereas Fixture EMI would affect mostly all Radio Frequency stuff - from MF (540 kHz thru 1100 kHz), through VHF and UHF.

What does the Interference sound like?
How many VHF FM Radio Channels are affected?
Is the noise level equal on all affected FM Channels?

Try "Seating" the Lamps first - rotate them in their Lamp Holders.

Then verify tight connections. Also make sure that both sides of the Lamp Holders are connected to the Ballast Lead Wire.

Verify the Lamps' Cathodes / Filaments are solid (not loosely vibrating).

Good luck.

-- Scott
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#199189 - 02/15/11 08:52 PM Re: Radio Interference and T8 Fluorescents Fixtures [Re: twh]
wewire2 Offline
Member

Registered: 11/14/02
Posts: 246
Loc: California
I just ran into that problem last Summer. I installed some
T8 fluorescent fixtures in a kitchen. There was radio interference. I bought the fixtures at a local electrical supply house and assumed they would be OK to use. I pulled those fixtures and bought a couple more at Home Depot. These one's specified they were for residential use. Same problem!!
I called the ballast manufacturer for information. They said the ballast number has an "R" in it if it is for residential use. I checked them and sure enough there was an R in the number. He said some of the ballasts are defective. They sent me 2 new one's free of charge. Problem solved!

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#199191 - 02/15/11 09:24 PM Re: Radio Interference and T8 Fluorescents Fixtures [Re: twh]
twh Offline
Member

Registered: 03/11/04
Posts: 898
Loc: Regina, Sask.
I'll have the home owner check the pins on the lamps.

The AM signal is perfect on all channels. The FM is equally bad on all channels. It sounds like static. It isn't a buzz or hum.

As to loose leads, they would have to be in at least three fixtures - one on each switch. It's a lot harder to get the home owner to check that. I missed my opportunity.

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#199376 - 02/23/11 10:09 AM Re: Radio Interference and T8 Fluorescents Fixtures [Re: twh]
sabrown Offline
Member

Registered: 12/12/02
Posts: 297
Loc: Ogden, Utah, USA
Have you tried more than one FM radio? I'm sorry for the suggestion, but I have been known to miss the obvious.

Still it is possible that the ballasts need RFI filtering, for commercial you often have to order RFI filtering separate. It is an inductive capacitor circuit, I would think that you could order it after the fact. I have not ever ordered fixtures with and have never had issues. Where as I know another engineer who used to swear by them and I never saw something from him without them.

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#199380 - 02/23/11 07:07 PM Re: Radio Interference and T8 Fluorescents Fixtures [Re: sabrown]
twh Offline
Member

Registered: 03/11/04
Posts: 898
Loc: Regina, Sask.
Originally Posted By: sabrown
Have you tried more than one FM radio?
The customer had two radios.

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#200072 - 03/19/11 07:45 PM Re: Radio Interference and T8 Fluorescents Fixtures [Re: twh]
MAH Offline
New Member

Registered: 03/19/11
Posts: 7
Loc: Saskatoon, Saskatchewan, CA
I am currently wiring a small shop, and have interference issues on FM with the newly installed T8 fixtures. The company I work for has chosen "clean volt" www.cleanvolt.net surge suppressors with the promise of reducing harmonics, voltage spikes, and EMI's etc. I am going to install one this Monday and will post results if any. The only issue with the units is there price is not as competitive as other similar surge suppressors.

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#200084 - 03/20/11 10:58 AM Re: Radio Interference and T8 Fluorescents Fixtures [Re: MAH]
LarryC Offline
Member

Registered: 07/05/04
Posts: 776
Loc: Winchester, NH, US
If the noise is radiated, versus being conducted through the wiring, the "surge suppresors" are not going to do much.

If a battery operated radio is fine, then the noise is on the power lines.

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#200387 - 03/29/11 08:42 PM Re: Radio Interference and T8 Fluorescents Fixtures [Re: twh]
MAH Offline
New Member

Registered: 03/19/11
Posts: 7
Loc: Saskatoon, Saskatchewan, CA
Well unfortunately I was unable to replicate the interference I was getting on the FM stations when I went back and the "Clean Volt" didn't do a damn thing for sound quality or clearness

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#200495 - 04/03/11 11:41 AM Re: Radio Interference and T8 Fluorescents Fixture [Re: twh]
pdh Offline
Member

Registered: 01/20/05
Posts: 354
Originally Posted By: twh
I'll have the home owner check the pins on the lamps.

The AM signal is perfect on all channels. The FM is equally bad on all channels. It sounds like static. It isn't a buzz or hum.

As to loose leads, they would have to be in at least three fixtures - one on each switch. It's a lot harder to get the home owner to check that. I missed my opportunity.


How far away does this affect a portable battery powered FM radio?

A very narrow or fast rise pulse can produce carriers all over the RF spectrum spaced at intervals twice its fundamental frequency. Lets say the pulse rate is 20 kHz (very possible for an electronic ballast). You'd get carriers every odd multiple of that. Both AM and FM demodulators would be outputting a 40 kHz signal. With AM you just would not hear it, assuming it even gets past the narrow bandwidth I.F. filter. With FM, the bandwidth is much wider to cover the wide modulation swings and the corresponding multiple sidebands that produces.

There are two ways this can affect FM. One is that the squelch circuit is being fooled to think a signal is present between stations. The other is that right on a station, the multiple carriers together actually look like phase modulation (which is very much like frequency modulation). If the pulse frequency is very unstable, its instability can come through as white noise on the FM receiver, whether tuned to a station or to an empty frequency. Instability of the pulse rate would actually be good in most cases by eliminating intermodulation with other RF signals, and that may be present in the ballast for that reason (without it, it can be serious source of interference to the aircraft radio band).

If this bad RF is radiating on the power line feed to the lights, then this RF can be blocked at that point with an RF filter. Ham radio ops wire up their own by passing all conductors in parallel (e.g. don't split out the NM) around a toroid core a few (3 to 8) times (need a large core to wrap NM in through it). An inspected installation may need a listed RF suppression device.

It might be possible to do this filtering inside the fixture using the smaller wires (parallel all of them that go to the ballast) so a smaller toroid core can be used. This would likely void the listing of the fixture, however.

If it is radiating through the light bulbs directly, a grounded wire mesh might be needed to cover the exposed side of the fixture. This is unlikely, but possible.

The RF would have to be in common mode to radiate on the line. In common mode, it would not be affected by a capacitor between conductors, or even to ground (where ground is carrying the RF, too). Induction in common (e.g. all wires parallel in the inductor) would be what would block it.

The ballast is definitely bad if it is leaking this much RF.

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