Fluorescent lights cause buzzing in intercom system

My guess is you didn't use twisted pair wiring for the intercom.

Another possibility is switch polarity of the power wires and see what happens.

New ballasts MIGHT help, but the electronic transformers on some low voltage lighting also causes noise on intercoms and AM radios.

Hi, First thing to do is to find out how the noise is coming into the intercom system, Through the air or AC wiring. All kinds of things we can try uing caps. inductors, chokes, etc. Try battery operated AM radio in the kitchen, do you here buzz?

Are you in a country that uses 50 Hz/cycle AC power?

TDD

Does that make me an Iconoclast? ^_^

TDD

From your post, I'm guessing that the buzzing occurs even when not using the icom ... right? The problem as I see it is that icom manufacturers seem to refuse to use balanced lines to the stations. There is usually a 'hot' input to the amplifier run to each station to the master where the amplifier usually resides. Station speakers are usually connected to the output of the amplifier, so they can be called. A lot depends on the particular design of your unit. I recently purchased a simple, now discontinued, NuTone icom/doorbell. Nice idea. It provides 2 indoor stations and 2 door stations with an electronic chime. But, if I put my ear close to the speaker, even when not using it, I hear a slight buzz. In my case it's not enough to hear, even in a very quiet house. But, in the instructions, there were all kinds of warnings to not run the wires close to electrical wires, etc. Yeah right, that's totally impossible. Even for this simple unit, it was impossible. When it is in use, you definitely hear some 60Hz buzz in the speakers. My plan is to someday redesign it but there are other priorities. Also, as an icom, it's not really that good. Unless you are close to the speaker, it's hard to understand. I previously designed an icom for my previous house that worked very well. There was no hum or buzzing and sound was very clear.

As to your system, do you use it as an intercom or just as a radio, as many people do? If you don't use the icom features, it might work to remove the input to the amplifier at the master. Filtering would be tough because it is harmonics of 60Hz which are in the same band as voice, that you are hearing. Different ballasts, i.e. electronic "ballasts" might help also. Electronic ballasts are actually a switching power supply at a higher frequency. You might try to replace the ballast on one light that produces the most noise with all the other lights off. If this works, you might have a chance.

Having had the same problem, my answer would be to find a wife who had dinner ready promptly at 6:00.

You can find in expense clamp chokes at some electronics supplies. I would first try power to intercom filter, then each line going out of main box, assuming there is a main box.

Let's see, 100 mf would draw over 4 amps. What? How big is the cap?

Greg

W hen I have installed caps, and preferably on the down side of an inductors, typically I use .05 mf 600 vdc caps. The most I use is .1 mf. Sometimes it works better with a resistor in series with the cap to prevent ringing, and they sell them that way. The caps should be inside an enclosure, preferably metal. Values for 120 vac lines.

Greg

"500 watts wasted?" -- Not if the power factor in the home is lagging. Then, the 100 mf capacitor would help to improve the power factor on the circuit and the power company would love you. (naw, I went too far).

Tomsic

Capacitors are cheap. Go to Radio Shack or elsewhere. Buy some ceramic caps in the range of .01 to .05, at least 500volts. Put them across the ac line right where the wires enter the ballasts. If you dont want to screw around doing all of them, just do one and disconnect the other ones. It could be just one light causing it too. Disconnect them one at a time.

Maybe the intercom should have had shielded wire going thru the walls???

If nothing else, try an electronic ballast on just one light, shut off the others and try it.

For car radio buzz from the cars ignition they make filters for the 12v lead. Of course you cant use them on 120v, but they may sell a 120v version. That would also be a capacitor, but has a choke too.

Thid might be a question to post to one of the electronics newsgroups too.

It was said once before by others, but I'll repeat it. There are two ways radio interference can get into the intercom: (1) through the power wires from the fluorescent ballast and (2) directly (radiated) from the fluorescent lamps themselves. The intercom wires or intercom units act like receiving antennas.

The gas inside an operating fluorescent lamp is a low pressure plasma and, like a spark gap a perfect generator of radio frequency interference, so the lamps are where the interference starts.

With am/fm radios, I've found both kinds of interference to be significant especially when the signal is weak, but fluorescent ballasts these days have to pass some FCC tests, so it's likely that replacing your T12 lamps and ballasts with T8 electronic types will help since the ballasts already have noise supression built in. Look for an FCC notice on the ballast label to that effect.

Getting rid of T12 lamps is a good idea in any case since they will be regulated out of existence later this year. T12 ballasts are already gone.

Check the grounding of the fluorescent fixtures. That's essential since fixtures can act like antennas too.

Tomsic

Nobody has asked - does this intercom connect directly to the 115v AC or does it have a transformrt?? Many run off of a transformer like a doorbell. Possible the filter capacitors in the low voltage power supply section are bad.

Nobody has answered the question either about whether twisted pair wiring was used to connect the stations - twisted pair provides common mode noise rejection which can eliminate induction coupling of the inputs to power lines, and also reduces the "antenna effect" which picks up hum from things like flourescents.

Also, are all the flourescents GROUNDED???

Unless Walter comes back, we may never know.

Twisted pairs would help, but if the circuits are not balanced on both ends, only ferrite clamps will help.

I pretty much gave up on getting rid of household wiring noise. It's so prevalent.

Greg

You can use cat 5 on the old ones too. heavier is better though - but you really NEED twisted pair - many older intercoms were installed without.