Household AC interferes with AM radio?

Phaserburn

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I was wondering if someone knows about this topic. No matter which radio I plug into my house's AC, it creates some static on the AM band. It doesn't happen on FM, only AM. It also doesn't matter which outlet in the house I use, or which floor or direction the radio is facing. There's a good place for a Superradio to get AM in my bedroom window. I get clear reception until I plug in the AC cord. On DC, it's fine. Anyone know why? Does my house have something wrong with it's wiring?
 

Steve K

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This happens with multiple AM radios? If so, then that rules out the radio as being the cause.

The way that you describe it, it does sound like there is some high frequency noise associated with the house wiring. There are two questions:

1. what's causing the noise (and can you disconnect/fix it)?

2. can you block or filter the noise so it doesn't interfere with the radio?

I've only seen noise generated from electric motors, or from digital electronics. Of course, almost all electronics nowdays has some digital circuitry, so there might be a lot of sources. I'd suggest unplugging all of your electronics, one by one, to see if the noise goes away. The more power that the devices uses, the more likely the chance of it causing noise.

You may have some luck with high-quality power strips to filter the power. I have some that use proper EMI filters to block transients and high frequency noise (so they say). This level of quality isn't cheap, tho. I think it costs about $50 or so.

If none of this works, you might consider just running the radio on rechargable batteries. I've gone one step further for one of my radios: I run it from an external nicad battery, and it is charged from a 1 watt solar panel sitting in the window! The battery is 4 amp-hours, and the radio only draws 30mA to 60mA, so the radio will run a looonnngggg time. The large battery also means that the meager solar panel will never harm it from overcharging.
This might not be practical for everyone, but I get some pleasure from the reliability of the system.

regards,
Steve K.
 

Sub_Umbra

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Hi-

This is a very common problem. It is usually referred to as common mode interference (I think).

The cause is usually that your power cable to your radio is acting as an antenna and is picking up a 60 cycle hum from your AC wiring and other potential radiators. Radio forums discuss this a great deal.

One solution is to wind the power cable around a ferrite core (choke) made of number 42 material. The choke should be as close to the radio as possible.

Radio Shack makes a nice core that they sell blister packed, in pairs for about $8 (?)

ferrite_closed.jpg
ferrite_open.jpg


As you can see, it opens up to make it easier to wrap. I think that the card that they come in has wrapping instructions. NEATNESS REALLY COUNTS HERE. These cores also may be snapped together for more effect.

Check out Google Groups with the terms (without quotes)
"ferrite ac interference radio"
for more. You may have to juggle these terms a bit.

Usually this happens with 'wall warts' and I'm a bit puzzled that it's happening on a Superradio as mine doesn't use a wart (Superradio III).

Another solution, as previously mentioned, is to run it on batteries. The Superradio III gets 400 hrs (!) on one feeding of alkalines and that's how I have always run the ones I've had.

Good luck
 

jayflash

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Some modern CPU based devices, especially high efficiency furnaces, emit broadband RFI. Try isolating the offender(s) by switching off circuit breakers or removing power cords. TVs, computers, and other appliances have active circuitry even when "off". If you find a device that's spewing electrical noise back into the AC line, try Sub Umbra's advice and put a filter on the offenders power cord. The thermostat wires from the furnace can act like an antenna too, so a ferrite bead at the furnace may help for those occasions.
 

Jack_Crow

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All,
The best fix for this kind of thing is the brute force approach.

Open or remove all the fuses and circuit breakers.
Turn on the radio and one by one power up various parts of the house one circuit at a time.

Sooner or later you will hit on something that makes the noise.

Things that have done it in the past are coils in door bell transformers, wall wart transformers, battery chargers, lamp dinners, x10 devices, motors in washing mech timers, various parts of the oil burners, humidifiers, thermostats, attic fans, and lamp balasts.

Ages ago I used to work in the AM Stereo business and got good at figureing out this kind of stuff.

Much luck
Jack Crow in Iraq
 

Sub_Umbra

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In re-reading this thread a couple things come to mind.

First, when I said,

[ QUOTE ]
These cores also may be snapped together for more effect.

[/ QUOTE ]

That may have been kind of vague. What I meant was that these cores are made in such a way that any number of them may be snapped together and then wound with the offending wire. Sometimes one core will not be enough.

Also jayflash's list of sources is important. Sometimes one must attack the problem by choking the radio cord and attenuating the sources of the signal. It can take detective work to resolve some of these problems.

Sometimes a problem can be resolved by something as simple as just moving another device's powercord to a slightly different position, like improving TV reception by moving an antenna. Sometimes it can be really wierd.

In addition to the keywords for Google Groups I mentioned earlier you might also mix in the word: toroid.
 

BF Hammer

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Radios made these days are engineered more with FM performance in mind than the AM band. The AM superhetrodine circuit does pick up interference from atmospheric sources, and when you plug into the AC power, the ground of the radio becomes directly connected to all the electrical noise conducted along the power lines. The circuit can introduce noise into the encoded audio at any or all points along the circuit path. FM radio uses the rate of change of frequency to encode sound, so it doesn't pick up atmospheric noise, and the first chance to really introduce noise into the radio reciever is after the intermediate frequency section of the superhet circuit, in the final audio amplification (assuming FM mono mode, there is AM encoding within the FM signal for FM stereo mode). Consumer-grade AM/FM radio receivers just don't get engineered to very high noise-rejection standards in order to keep the cost down in a price-driven market.

Just wondering - do you or anybody in your neighborhood (meaning on the same distribution transformer of the power utility on the street-the black keg-sized things on some utility poles) use a "wireless" telephone jack or home computer network? Those are the devices that use the electrical wires of a home to carry the signals for a remote phone jack or computer network. The signals get weaker with distance and don't carry very far outside of a home, but could still be just enough to cause you trouble with your AM radio reception.
 

brightnorm

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One other thing you can do is tune your AM radio between stations, turn up the volume, turn on all electrical devices and go through the house and see if the noise seems to get louder in a particular area or location. I've found this useful in determining interference from my X10 remote system. (Though in that case Jack Crow's approach was also helpful)

Brightnorm
 

Sub_Umbra

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[ QUOTE ]
BF Hammer:
Radios made these days are engineered more with FM performance in mind than the AM band.

[/ QUOTE ]
Not this one.
I'm assuming that Phaserburn has a Superradio III ( If he has one of the old 'IIs' he should definatly hang on to it. ) No matter which GE Superradio he has, they are all optimized for AM (medium wave).

The SR3 has:

--Tuned RF stages on both AM and FM
--A ceramic FM IF filter
--4 stages of AM IF tuned circuits
--A 200 mm ferrite loopstick antenna

This low-priced radio has no frills other than a very nice 6" speaker. It is, however, built for DX (long-distance listening). These radios perform all out of proportion to their price.

Their AM band tuning is really hot.

The FM band is no slouch, either. I hooked a TV antenna to an SR3 7-8 years ago and IDed a FM broadcast station in Florida -- 500 miles away! No flames, please.

While quality has become an issue with the SR3 of late one still must spend a great deal more money to to get anything even marginally better for an AM DX rig. Because of its battery life, it is unsurpassed as a hurricane radio.
 

Sub_Umbra

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[ QUOTE ]
jayflash:
Last summer I listened to a Florida FM station for 20 minutes. The station blocked a closer one in Wisconsin!

[/ QUOTE ]
A lot of people will just go nuts if you try to tell them you did that.

Some out towards the edge types DX TV. (another FM band) They call it 'Snow Band'. In the days before digital cameras they would sit with a polaroid camera on their lap and try to take a picture of some far off station ID. Ocasionally trans-Atlantic IDs are made! Aside from a hi-gain antenna and a rotator, they also have to use a PAL TV for Trans-Atlantic DXing. (I think)

Radio rocks!
 

Phaserburn

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I do have a SR3. And thanks to everyone for all the tips.

Ok, after reading this, I have come to this conclusion: my home is a poor setup for AM reception using the AC. It has aluminum siding, 20+ dimmer switches, humidifiers, tons of wall warts, wireless intercom (using the AC lines; disconnecting it didn't fix the problem) 4 stereo systems, 3 PC's, etc. When my wife and I got married a year ago and moved into the house, we had the "duplicate appliance" problem... Anyone need a microwave, washer or dryer?

So, I've been using DC when I want to listen to AM. Mostly I do it for the great dedicated news and sports radio stations out of NYC, like WFAN, WCBS and WINS. If I recall correctly, WFAN is 50,000 watts. In the evening, one should be able to hear that one at a distance! I wonder if they power down at night.
 

Stefan

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Just a possible suggestion, but I read somewhere that your radio has an external antenna jack. Maybe something can be long enough to be plugged into the radio on one end, and hang out a window on the other end. Its almost the same setup I have with a radio scanner.... the included antenna that comes with it is not that reliable.
 

jayflash

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Phaser, if you've got an attic, a long wire antenna could be installed up there - providing there's enough room to work. An insulator at each end of the wire and a drop line to your radio should do it. That may help to receive more stations - of course it may pick up more noise too. You'd have to experiment. If the radio has a grounding screw, try grounding it. That may improve your signal to noise ratio even when using batteries.
 

eluminator

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Light dimmers will kill AM reception more than anything else I know of. Even a neighbor's light dimmer. Other things around the house can interfere with weak signals also. Sometimes fluorescent lights or computers will do it. Arcing insulators on power poles, electric motors with a bad starter switch, the list is endless.

I have a Superradio that must be 25 or 30 years old. It's the original, before they started numbering them. They are the best for AM reception, and last for months on a set of 6 D cells. I'm glad to hear they are still making them.

Certain atmospheric conditions can allow TV and FM reception from stations several hundred miles away. It's called tropospheric ducting.
 

Sub_Umbra

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[ QUOTE ]
eluminator:
Light dimmers will kill AM reception more than anything else I know of. Even a neighbor's light dimmer. Other things around the house can interfere with weak signals also. Sometimes fluorescent lights or computers will do it. Arcing insulators on power poles, electric motors with a bad starter switch, the list is endless.

[/ QUOTE ]

Another source that can be very troublesome is old or poorly installed cable TV wiring.

Unfortunately, anyone living in the Western world gets blasted with more RFI every year. It's too bad.
 

Jack_Crow

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PB,
Back when I was doing the AM Stereo thing we had an antenna in the office.

It was a Palomar. There was a box on a short post over a base. The box was an antenna that could be pointed, and tweeked for frequency.

We used to pick up Day Time stations, indoors from over 500 miles away in good stereo! I have no idea where one of those can be dug up.

Go on Ebay and look up 'broadcast electronics', 'studio monitors', and other items a broadcast station would own to keep track of it's signals. Sometimes bargans can be found.

I forget who made Mr. Kahn's studio monitor but it was a neat radio. Thumbwheel selector for frequency, and a real good S meter for signal readings. It was a special hack of a standard product for stereo service.

We sold a stereo adapter that took the IF output and converted it to L and R. The studio monitor would deliver 30db of seperation while a good consumer radio would deliver 20db.

Look up a bunch of hams called SPAM. Or the Socicity to Preserve AM. They tend to hang out in the 160m band (about 1.9 to 2.3?? mhz). I sure they have a web site you can extract some tips from.

Also a lot of car radios can be made use of. We used to modify them for FET pre amps as well as stereo demodulation.

Their main advantage is coaxial feed. Keep in mind most car radio antennas are 10 ohm feeds and that should be figured into the mix. Why 10 ohm, to surpress (shunt) impulse noise in the automotive environment. That's why you don't see too many plastic case car radios.

Check old radio magizines for filters, antenna designs, and converters. Lots of good projects if your willing to make the effort.

Is your Super Radio set up for 1620 to 1800? The extended AM Band?

AM here in Iraq is kind of dull. All Arabic programing. This month is some kind of holiday, and nobody is broadcasting music here.

Had a number of radio clubs back home ship me parts to make a low power FM Stereo station for the troopers. At about 25mW it covers the base with portable radio. It will be fed with an MP3 player.
Got to wait till the base Mayor a LT Col get's approval from higher ups for me to turn it on. We don't want the children of Islam to hear rock and roll do we?

Good luck on your project.

Keep it warm
Jack Crow in Iraq
 

eluminator

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And I should have included aquarium heaters. I never had one but I'm told they use the simple light-dimmer approach of switching on part way through the AC cycle for power control rather than the more sophisticated integral cycle way, so they are equally noisy.
 
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