A year or so ago some source of interference with AM radio appeared in my neighbourhood. I have one in the shower that I can rotate to minimise the effect, but it’s always there. The best orientation is roughly, but not exactly, the same all the time. Any other orientation us unlistenable.
Is this orientation a clue as to where the source is? Should I wander around the house with that radio and try and triangulate the source, would that be useful? Is it even likely to be in the house, or external?
It is worse the further down the spectrum I go; sadly my usual stations are 573, 630 and 702, at the bad end.
Every now and then it goes away, or nearly so. I think more often on weekends, but not at all reliably.
FM and DAB are not affected of course.
On a related matter, when listening to AM in the car there are certain road intersections with really bad interference. They tend to be fairly major ones in general, but by no means does it happen at every major intersection. What’s likely to be going on there?
We have some dimmer switches, couldn’t say as to the type as they were here before I was. But they long pre-date this problem. Would twiddling them be useful diagnostically?
Just at intersections though? I’ll have to pay more attention next time though, thanks.
In Australia? First I’ve heard of that. Why would that be?
But no, we haven’t noticed a day/night factor here.
Can you think of a use case for one that would fit the facts, though? It can’t be the fridge as we’ve changed ours in that time, for instance. Don’t have an air conditioner going all the time.
If the radios are powered by house current, you can add a ferrite core to the cord and or use chokes and capacitors to filter out the interference. Look it up on the internet, you should be able to find a few plans to diy. You can also contact your local amateur radio club and they will gladly search the source of the interference, they love that kind of a challenge.
The reason am radio stations reduce their power in the evening is because that is when the ionosphere is mostly opaque to radio waves and they will reflect back to earth at a distance and interfere with local transmissions. Something like that anyway.
What’s around your house? It doesn’t have to be that close. All sorts of electro-mechanical devices could be a problem. If it makes a spark it can be an AM transmitter.
As others have stated, interference can be from many sources in your house or surrounding structures. Best thing is to make sure it’s not originating from anything in your house and I’d consider pulling breakers to verify you don’t have anything creating the problem.
Believe it or not, the FCC is your friend in this area. They have a daily digest that reports actions taken when this type of problem is found and they really do send people out armed with antennas and spectrum analyzers. You can report it here: https://www.fcc.gov/consumers/guides/interference-radio-tv-and-telephone-signals
You can try to triangulate the interference with the radio. The minimum interference will be when the long edge of the radio is pointing at the source, and maximum when the source is broadside to the radio.
AM radio is quite susceptible to all sorts of hash, generated by al sorts of sources. A clue will also be in the actual sound of the interference. Dimmers have a characteristic 100Hz base buzz (in Oz), one which changes in character as the dimmer level is changed - at full power the dimmer should create no interference. Electric motors with commutators can be a bad source of interference. As are generators. They are a more diffuse hash sound. Being better on weekends does suggest a commercial/industrial source.
Warning: borderline on-topic Ol’ Days story incoming
Back when I was a wee strapping lad, I had [del]an onion on my belt[/del] an early microcomputer: a Radio Shack TRS-80. Because the FCC wasn’t yet hip to how some of that electromagnetic interference thing worked, it had a cheap unshielded plastic case covering some of the most electronically noisy circuitry ever known to man.
You could turn on an AM radio anywhere in the room (say, within 20’) and tune it anywhere on the dial. If the TRS-80 was running, you’d hear a constant drone pitch in the radio: RF emissions of the computer’s circuitry. This drone responded to activity within the computer itself: the system idling on a prompt made a different noise than the computer running a program, and different activities in the program even sounded different.
One of my proudest moments in my early geekdom was writing a program that would play music over the RF interference by controlling the speed (number of instructions, instruction cycle times, etc.) of the execution of a loop to correspond to different notes.
No sparks. Just the sweet sweet music of electrons scurrying frantically around a circuit accidentally designed to give them lots of little antennas from which to emit RF noise.
This is where you start. You could walk around with a transistor and try to find the source. Things to look at are switching power supplies (new computer in last year?), wall wart power supplies, flourescent lights of all kinds, (any new-tech lights of ANY kind?), electric motors, light dimmers, -could- be a transformer or loose connection on a power pole or something happening at a neighbor’s house.
Also, the electric company could have a defective transformer in your area.
Assuming your neighborhood has overhead wiring, look around for one or more large, probably gray, cans about the size of a trash can, mounted up on a pole somewhere around your house. Get a battery radio, or use your car radio, and see if it gets worse as you get near the pole with the can(s) on it.
If that’s it report it to the power company - I believe they’re required to fix it. Its in their interest to do so anyhow. It may be near failing.
On another tack - do you neighbors have the same problem?
Thanks folks. The shower radio I mentioned is of course battery-only, so I can use that to triangulate, now I know the long axis points to the source at the orientation of minimum interference.
And asking the neighbours is a good idea too.
We’re in a quiet suburban area, no industry or anything.
Could it be, that the transmission tower(s) that broadcast these AM signals for your area have been moved, changed, relocated etc? If you are right on the fringe with respect to signal strength any interference (which perhaps has always been present) may become more apparent.
I’m sure there are maps which show where commercial broadcasts are made and repeated from. Probably some complex legal requirement from the ACMA ( http://www.acma.gov.au/ )
just of interest, here ( http://i.imgur.com/RcHVFMX.jpg ) is a map of the AM broadcasting locations in Sydney. The items all in capitals are the broadcast locations, the places in normal text are just location identifiers.
How far are you from your nearest, maybe give them a call and tell them you are annoyed at their shoddy transmission quality
