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Discussion Starter #1
As I acquired an old car radio from someone who was upgrading, I decided to tinker around and see how I could set it up in-home. Using a regulated DC power supply with the power leads going to the positive terminal and black wire (ground?) going to the negative terminal based on information I was given, the radio actually works fairly well except for one thing: AM interference.

Now, I do realize troubleshooting AM interference is a tough thing in the best of cases, but here's where I'm a bit confused. If I don't have an antenna attached (either a thin wire or a car whip antenna), the background noise generated by the receiver is barely present. When I attach an antenna though, there's a fair amount of buzzing. I'm sure it's not my power supply, as with no antenna the noise floor is pretty low and the power supply I'm using is somewhat designed for this kind of use (transceivers, for instance). Moving the antenna beside the power supply also doesn't change the noise level.

Could this be a grounding issue, or is it more likely just RF interference in my home? If it is a grounding issue, how can I remedy this?

This is mostly just a side project to learn a few things, so I understand if this doesn't work. It would be nice to have a decent tuner though.

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Can you try using a battery, instead of the power supply? Power supplies can generate noise. Try moving the antenna around. If you have a loop antenna, you can easily move it to locate noise sources. Even moving a wire antenna may show where the noise is coming from.
 

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Discussion Starter #3
I don't have a battery handy unfortunately. Moving the antenna doesn't seem to affect the noise level (even if I put it directly on the power supply).

The unit I'm using is a Tripp-Lite PR4.5
https://www.tripplite.com/4.5-amp-dc-power-supply-13.8vdc-precision-regulated-ac-dc-conversion~PR45

Maybe I'll have to see if I can track down a battery and charger to see if that helps (given the noise level doesn't change). I just figured it wasn't the power supply as with no antenna connected, noise is very low.

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Power supply noise can be radiated to the antenna. Can you move the radio elsewhere? Maybe it's a noisy location.
 

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Their are many sources of AM radio interference, including power lines. About the only way to get rid of it is to go out into the country to a road with no power lines or electricity nearby. I noticed this many years ago when traveling on country roads and highways. On the car radio, reception was great until I turned onto a road with overhead power lines and the station would get drowned out with noise. The further into the city I got the worse it became until only local stations were receivable. Even those were not always that clear. I noticed a similar thing when we had the province wide blackout. I turned on a portable battery radio to see what was on AM. I picked up radio stations I hadn't heard in over 30 years. When the power came back on, the whole AM band was full of static with only local stations receivable.

There are ways to troubleshoot the source of AM noise. A battery operated portable AM radio is the best way. Tune to a station where some noise is audible along with the content. Travel around the house to see where the noise is loudest. If the source can be located, turn it off to see if the noise goes away. Repeat until all local sources of noise are determined.

The next thing to do is to determine if the remaining noise is internal or external to the house. to do this, turn everything off. The best way to do that is to turn off all the house breakers at the main panel. Make sure to not disrupt things like PCs (shut them down) and PVRs which should not be recording or have pending recordings. Now check for noise. If it's gone, the source is internal. If not, it's external. Now turn a breaker on and check the noise level. If it increases, check everything on that circuit. Repeat until done.

It's almost impossible to get rid of AM noise in modern homes. Almost everything from light bulbs to furnaces have digital circuitry that emits some level of noise. I've even seen radios that interfered with themselves. Good luck.
 

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but here's where I'm a bit confused. If I don't have an antenna attached (either a thin wire or a car whip antenna), the background noise generated by the receiver is barely present. When I attach an antenna though, there's a fair amount of buzzing.
+1 to ExDilbert's response... good strategy...
To possibly clarify your stated confusion.

There are two main types of trash that can influence AM radio reception by raising the noise floor. Conducted emissions and radiated emissions.

Conducted emissions are those that enter a receiver via the power wires or other cabling... Thus why it's called conducted.

Radiated emissions are those that are emitted over the air and are picked up by an antenna, thus why it's called radiated.

I guess you could also say some sources of really bad IX can be classified as both conducted and radiated however.

Good Power supply ur using IMO, it is not a junk chinese switching power supply.
In my house I once found a really bad switching power supply that came with a PC based satellite tuner was the main offender. I replaced it.
While in my brother's house his main offender was a dimmer operated light fixture in his dining room. He turned his lights off and his IX completely disappeared.
 

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Discussion Starter #7
Thanks everyone! I'll try some things and see what happens. :)

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Discussion Starter #8
Still working on improving the AM reception, but I'm starting to think it could be the DSL modem upstairs - either that, or our wireless thermostat. I've shut down everything pretty much down here (minus the HVAC system) yet the noise is still present.

Now, using my portable radio in the area on battery power shows little noise (certainly not the buzzing sound the car radio unit is getting). Moving the portable radio near the car radio head unit does generate some buzzing interference, as does moving it right beside the power supply (understandable there).

Maybe I do want to track down a battery or at least try moving the radio to another part of the house.

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It sounds like the power supply might be the issue. A transformer based power supply would be better than a switching power supply but they are more difficult to find. A better quality switching power supply with RF filtering to reduce noise might help. It might also help to install an RF filter on the power line coming out of the power supply. It could even be the radio itself.

Moving the antenna might help. It should be possible to find a car radio antenna cable extension or an antenna with an extra long cable. Outside or near a large window would be the best location for the antenna.
 

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Discussion Starter #10
Mine isn't a transformer-based PSU? Hmm.......

I was trying to not use a switching power supply (like a computer PSU).

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You might want to try locating the Power Supply well away from the Car Radio and the (too small) AM Antenna your are currently using.

Even better, you might [also???] want to try locating an INDOOR [or OUTDOOR] AM ANTENNA as far away from the Power Supply as possible. I surveyed Indoor/Outdoor AM (and FM) Antennas in the fol. post....be sure to use a SHIELDED Coax and bear in mind that AM Loop Antennas will have a NULL in the Plane of the Loop which can be rotated to minimize reception of Interference:
https://www.digitalhome.ca/forum/26-am-fm-internet-radio-music-industry/274609-clock-radio-good-reception.html#post2922681

PS: From the description of the Tripp-Lite Power Supply/Battery Eliminator I don't think it is a Switching Power Supply....if it were, they would have advertised this newer technology....also the unit would be MUCH smaller & lighter.
 

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Discussion Starter #13
I'm pretty sure it's interference picked up on the AC lines. May try an RF filter if I can find one I don't have to order from China. (heck, if they were easy enough to pop off, I'd take the one from my old laptop's charger cable even as a quick test).

Things were quite a bit worse on an outlet closer to the back where our actual power lines come into the house, but given the portable radio isn't too noisy by them, I'm not convinced they are the direct source of the interference. Maybe our furnace / central AC unit? (both are relatively close to the second location I tried plugging in.

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BGY11, I also believe it is your power supply. From the pictures it looks like your power supply has only two prong power plug so it is not grounded. I would run a piece of wire from copper cold water pipe to your power supply and see if this helps. Also place the power supply as far as possible from the radio. Try to ground the radio to see if it will make any difference. Even the best power supplies create problems for AM reception. Indoors AM antenna will pickup noise from everything.
 

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Discussion Starter #18
I'm honestly thinking my power supply might have an issue - reviews of other Tripp-lite PR units seem to indicate no noise when using ham radios and such, and even the power supply itself seems to make no noise (mine definitely has an audible hum and the chassis seems to vibrate)

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One key thing i heard was "old" car radio. Older car radios may not have enough emi shielding from higher voltage hydro sources. My car radio is not old but also not top of the line and i hear loud buzzing when ever I drive under High Voltage Hydro wires.
 
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