[morzh]

Someone (I forgot who it was) has already posted a thread with the same effect described in, when a particular load is turned on and the hum disappears.

I then replied that this is the case in my big room - I turn the lobby lights on and the radio that has a strong buzz when tuned in stops buzzing or the buzz (hum) gets reduced by a lot.

Well, I have just confirmed that it is the case pretty much around the whole house: in my 90 on my working table in my office the hum practically stops when I turn on that lobby lighting fixture which BTW has 8 CCFLs in it.

This so far is the only load that has that effect on the reception.
Light in the adjacent rooms or in the office do not have eny effect.

Since I do not know my house wiring in fine details, I could only theorize the load is just in the licky place, like an end of transmission line and it terminates it.....

Beats me.

[BrendaAnnD]

Interesting that a capacitive load would do that. I would think it more likely that an inductive load would. Learn something new every day.

[morzh]

Ideal load to do that (I mean if it were a transmission line) would be a matching resistive load. Which it is neither. And then it is an unaswered question where it is in the line.

Capacitive, if it were (I do not know - never learned what kind of load it is in a CCFL, I always thought it is similar to other fluorescents) - why then the other fixtures do not do that. They do not necessarily have 8 bulbs but then they have 3, so I should've at least notice some effect but then there's none.

[LASJayhawk]

How about this. The lights are putting out additional noise, but are on the opposite phase of the primary noise source, canceling it out? Like the way the hum-bucking coil works.

Some of this is black magic. I have a RCA T-60 and a Philco Jr. sitting next to each other. Tons of noise on the RCA, none on the Philco. I traced it back to the wall wart for the answering machine. Seems the RCA line coupled antenna no like wall wart.

The Plasma TV trashes almost everything, but radios with loop antennas fair much better than long wire sets. BTW: the TV radiates so much hash that I can pick it up on my scope if I touch the probe tip. It's an ugly looking 35KHz signal that I assume must be the power supply.

[Chuck Schwark]

Tighten all the Hots, Neutrals and Ground returns from all branch circuits in your breaker box. Be sure the ground bond strap in the box is tight too.

Do this with each branch circuit breaker OFF obviously.

If there are no ground wire returns, then you may have poor or corroded box to conduit (or BX) connections in your circuits. Maybe a open neutral in a circuit, which then relies on a poor ground return thru the conduit/BX causing the problem(s). Standard 3-lamp outlet testers can detect this.

Just some thoughts…
Chuck

[morzh]

Chuck

Thanks, could be something to check.

But why just one fixture doing this?
And, again - why is is TUNED hum, it only exists when tuning to the station.

[BrendaAnnD]

Intermodulation. Low frequency AC is imposing itself upon the RF because the mains wiring is becoming part of the antenna. When not on a station, you won't hear it because the IF is not passing a signal.

[morzh]

Today I took my small pocket transistor radio (the antenna of course is the ferrite type so it is highly directional) and heard this buzz when tuned to this very station (and none when tuned to others) in only particular direction, where it becomes extremely pronounced. The buzz exists everywhere in the house.

Because now I could move freely around and keep listening to the buzz, I verified the effect of all the loads in the house (well, the lights) and I saw that the only load that totally kills the buzz is that lobby fixture - once the switch is flipped the buzz disappears. The other loads have zero effect.

I do not want to go into the distribution box while I am alone in the house, but maybe I should try to flip the breaker that controls that part of the wiring and see if it still persists, and maybe then try to tighten the bolts.

And I just thought of something: this is the only hanging fixture in the house and it has a long vertical wire coming down. I have a feeling that there is some nice loop formed in the wiring that eventually leads to it.


PS. I turned the breaker off that is responsible for the lobby fixture and the buzz went away.
Yep, will try to tighten that one.

[TA Forbes]

It is important to remember that "Tuned Radio Hum" has absolutely nothing to do with "Dynamo Hum."

[gregb]

I have found in my house that any flourescent light almost anywhere in the house will cause this issue as well as touch lamps. They cause not so much a hum as a static thats seems to extend right across the broadcast band. When I built my work bench and radio room I did install fluorescent lights throughout except over the repair bench I installed standard incandecent lighting and when testing I shutoff the fluorescents and have no issues.

Gregb

[morzh]

Greg

This is a different issue. You have interference emitted by a load. I have something else - my wiring becoming a part of a receiving contour and then 60Hz modulating the received signal.
And in fact when I turn a particular load (which is a CCFL and not incandescent) - the hum disappears. It is without any load that it is heard, only when tuned in.

[gregb]

Ah yes, I had that backwards. I do have one station that always has that modulated hum no matter what radio I use and some worse than others. Nothing I do ever seems to get rid of it. It have try turning things on and off and tightened wiring connections. Not sure what else too try.

Gregb

[morzh]

I am pretty sure it may involve a badly routed line where the hot comes from one place and the neutral - from other.
I know for a fact I have a line like it in my house. And it is in the same vicinity that the switch that cuts the hum. Might be the same line.
They form a loop.

[gregb]

That could be in my case though in the new part of my basement I did all of the electrical so I know its all good but the rest of the basement looks like it was done with economy in mind and hard to say. I do plan to reno the rest of it and rewire and insulate so will keep a close eye out for wiring errors like you describe.

Gregb

[David]

Sometimes when folks install a switch for lighting they switch the neutral not the hot wire. Easy to check remove switch cover plate then switch from box. Using a volt meter, with switch in OFF POSITION check from each wire of the switch to a receptacle first to neutral then hot of the receptacle. If switch is wired correctly you should only get a voltage reading when going to the neutral side of receptacle. Hope that makes sense not hard to do David