rfi from house wiring ?

[G4KIN]

Wonder if anyone has any idea on the following
I moved to a new qth about a year ago. set up the shack and everything from BCband to at least 500mhz is wiped out with hash every 5 mins for approx 50/60 secs
Now then......out side we have a street light but I got them to check it out and they came and pulled the fuse while I monitored the noise ...it was still there ! Thermostat I hear you say wellI have asked 2 sets of neighbours to to pull the plugs and it is still there . I took a small BC rx and ran around the house and next door ,it peaks up somewhere between the front of the houses the party wall .
my next door neighbour has cable as do I . I rang them up and asked if there was any likelyhood of anything there going pear shaped ...they wouldnt hear of it and fobbed me off .
I replaced the dimmer switch in the front room downstairs with a conventional double switch ...that made no difference . Then I realized that if I turn the downstairs switch off at the rcd unit the noise stops ! this only happens when I kill the power to the 4 lights on that circuit ...thats all there is on that circuit . The noise certainly has a pattern ...is it likely the downstairs circuit is acting as the antenna from the external rfi would a mains filter before or after the rcd unit help

would appreciate ANY comments on this

Phil G4KIN

[W8JX]

Check refrigerator(s) as it has a defrost timer.

[WX7G]

You have troubleshot the problem to the four lights on the downstairs circuit. Now you can finish troubleshooting that circuit.

[G4KIN]

Thanks for the comments on the rfi from the house wiring or the downstairs lighting to be more precise. I keep coming back to the lights in that there are 4 of them and at the moment they are standard incandesant lightbulbs  but the fact of the matter is the rfi goes when this circuit is knocked off ! I took the lamps out but the rfi still appears every 5 mins  . I have spoken to the neighbours who have been quite sympathetic to the point that they have knocked of their a/c while testing in the shack. but it still there . So it is further afield I guess but the question I keep coming back to is why just the downstairs light circuit .
Latest test was I took a rx into the garage a little further down the yard connected the antenna feeder from a GP and powered the rx from the garage a/c which although come from the meter cupboard in the house via an isolation switch at that point then to a RCD unit at the garage there doesnt appear to be a problem .....

neighbours inform me that they get the rfi on their broadcast radios as do i ,also my neigbour on the other side says she is getting noise on her new cordless phone !!
a shack move is looking more likely in the spring.

thanks again for all the comments

[WX7G]

It would seem that there is something on that AC circuit that you are not aware of. Can you simply shut the circuit OFF and use a different source of lighting?

The neighbors RFI problems may or may not be the same as yours. An experiment to try is to shut your light circuit off for an evening and ask the neighbors if their RFI was still present. Do not transmit during that time as your transmissions may be the source of their RFI problem.

[AA4PB]

Maybe you have a transformer to power a door bell or some other device powered from that lighting circuit. Small transformers like that often have a thermal cutout in lieu of a fuse and those have been known to go bad and generate RFI.

[K1CJS]

The only real way to find the RFI at this point is to trace the circuit from point to point--problematic in a finished home.  Are you absolutely sure that the four lights are the only thing on that circuit?  Could there be a photocell or a similar device for a front porch/entry path light on the circuit as well?  Anything with an electric/electronic timer or switch could cause the RFI.

If all else proves to be OK, the remaining alternative is to open each junction/connection box on that circuit and check it.  Could well be that there is a loose connection in one that seems to be timed, but isn't.

Good luck and 73!

[G4KIN]

thanks again for the input ....like some of the replies my concern is that something is running unknown to me !! I have only been in this house for 1 months and it does have some 'dubious' wiring which I have dealt with .
I was wondering if I get the electrician to move the down stairs a/c feed to perhaps the same loop as the upstairs lights and see if that eliminates the problem .
My bathroom does have some 12v 20w lighting system which does give off some hash when they are switched on ( I only noticed this today ! ) does anyone think the transformer could produce this 5min periodic rfi ....perhaps capacitors charging/discharging ?
but thanks to all I will check them all out this weekend .

phil
g4kin
shoulda stayed in GD land ..... non of this ....hey ho !

[WX7G]

It should be a simple matter to track down the noise source. Switch OFF the breaker that shuts OFF the noise. See what devices are without power. AC, bathroom lights, and so on? Don't get dide tracked by other, different noise sources.

[KD6KWZ]

I've heard of power wire terminal/junctions, that were slightly loose, could generate RFI noise. This doesn't happen often, but something to look at.

Yes, you could have some unknown additional circuits tapped into that light circuit, especially since you already said they have "novel" wiring there. 

[K0IZ]

With lamps removed, how about using small AM radio, tuned to top of band.  Try to follow wiring from circuit breaker box onward?