weird interference on AM radio

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Hello! I have a Chevy 2013 Malibu. Nobody has been able to find the following problem, not the dealer, not my own mechanic, nor a car audio guy I know....

I am a big sports radio fan and enjoy AM radio. For some reason when running the A/C I get a whistle whiny sound and to make it worse, while charging my phone, I get a hiss/static noise. This doesnt happen on FM or it is very minimal while listening to FM. When I run the A/C full blast the whiny whistling sound pitches higher then finally goes away....Also when I unlock and lock the doors, you can here a quick noise of static through the speakers while the AM radio is running.

The radio sounds fine with no phone charging and no a/c running....Any suggestions? Thanks!
 
Oh man this will be [censored]. Modern cars put out all sorts of harmonics. Even from passing cars I can get the whrilllllll from their engines on the radio.


https://www.popularmechanics.com/cars/how-to/a84/1272491/

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Now that you've pinpointed the noise, what can be done about it? It depends on whether your RFI source is broadcasting or cabling the noise to your radio. This matters because the cure is different. Try pulling your radio's antenna lead out. If the noise goes away or is substantially quieter, it's coming in through the antenna. If the noise stays the same or gets louder, it's coming in along the 12-volt power cables.



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A cheap AM radio makes a good Geiger counter-style device for hunting down RFI. Here, we're looking for an alternator with a bad diode. Mind your fingers.
 
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My dad told me about this decades ago. He said that 99% of people dont listen to AM radio. And that the AM receiver in newer cars was built poorly and that the FM was built much better for this reason. Am is more susceptible to noise from outside sources, throw in poorly made noise filters or none at all and you get poor AM reception.
 
Welcome to AM. You can try shielding, filtering, improving the stereo but the frequency coming over the airwaves is still going to be corrupted at times.

I recall when I first started driving, at a certain time at night I'd get an AM station from somewhere in California. I lived on the East Coast at the time.
 
Originally Posted By: JLTD
Welcome to AM. You can try shielding, filtering, improving the stereo but the frequency coming over the airwaves is still going to be corrupted at times.

I recall when I first started driving, at a certain time at night I'd get an AM station from somewhere in California. I lived on the East Coast at the time.


AM is amplitude modulation and is more susceptible to noise than FM. That's why they used to have resistored spark plugs otherwise you'd pick up noise from the engine. Not much you can probably do about it. You could try a different type of charger, it's probably the circuity in the charger that's putting out that noise. Try wrapping it in aluminum foil.

Also AM is almost like short wave, travels further in the ionosphere at night, in daylight the sun tends to kill the signal.
 
The big difference in the 1970s was in the tall metal fender mounted antennas. Printed on the window or little stubs are not going to work well with the longer waves of AM.
 
Originally Posted By: JLTD
Welcome to AM. You can try shielding, filtering, improving the stereo but the frequency coming over the airwaves is still going to be corrupted at times.

I recall when I first started driving, at a certain time at night I'd get an AM station from somewhere in California. I lived on the East Coast at the time.
that's called skip. Am radio waves travel much farther at night.
 
Try a better phone charger, cheap circuits gives off electronic noise. Also check the grounding on your radio. All else fsil. Look at in line filters. Ferrous filters..https://youtu.be/jbv9PUC0xPk
 
Got a great stereo and the AM acts up in Kansas City around 11am. Its like it trying to interfere with my listening to my advanced conservative studies on the EIB network with Rush. I like XM Radio but its gotten really high in price.
 
Originally Posted By: Marco620
Got a great stereo and the AM acts up in Kansas City around 11am. Its like it trying to interfere with my listening to my advanced conservative studies on the EIB network with Rush. I like XM Radio but its gotten really high in price.


How much are you paying for Sirius? I normally call them and tell them I'm going to cancel unless they can give me $30 for 6 months. Been doing it for years. I think there's a thread about it around here.

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4678001/Re:_Who_here_has_satellite_rad#Post4678001
 
Avoiding interference in the AM band is a huge problem these days for electronics, many circuits will switch right in that range and that's not even thinking about harmonics. AM is a pretty crummy old technology when you get right down to it.
I would try an OEM charger if you're not using one already (assuming that your phone is a major brand) and also make sure your battery connection is rock solid, that's a nice big filter on the line in your car even when it's being charged by the alternator. A super cheapo charger from the dollar store is not likely to really meet the EMI standards it claims, one I bought at DG actually makes a fair amount of audible noise but I don't care in its application.

BTW, I use Sirius but it will get hosed up by power lines on my way to work and also drops out in patches when I drive up to ski...it's not totally reliable, either.
 
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Years ago I had interference on an aftermarket AM radio from the blower motor for the HVAC. I reduced it to almost zero by putting a capacitor in line with the radio feed wire.
 
So - the whistling with the AC is either the fan motor itself or a pulse-width-modulated speed controller if that's used instead of the standard 3 spd resistor pack.

The hissing from the phone charger is from the electrical noise created by the step-down converter in the powersupply which rapidly turns 12v on/off really fast and shoves it through a filter to allow ~5V out the back end.

both of these emit pulsed radio frequency which is picked up by your AM reciever either through the air or thru vehicle wiring. It is not necessarily a "quality" issue with the receiver.

You may be able to reduce it by clamping a couple of ferrite RF chokes over one of the AC fan wires (if the cable is both +/-, do not clamp both in the same bead). OR run the fan through a noise filter, or a large coil of wire which is thick enough to handle ~20A current.

You may also be able to put ferrite beads over the radio power lines as well; inserting a power filter was a common practice in the 80s for dealing with this kind of thing.

To deal with the cel charger interference, you'll have to experiment to figure out if it's through wiring or RF. May just be easier to try different chargers, or use an extension to charge it from a different 12V outlet, or perhaps built an 12V extension with a power filter built in.

google "ferrite bead"

-m
 
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