[ExDilbert]

mine definitely has an audible hum and the chassis seems to vibrate

That's not unusual with conventional 60Hz transformers. It doesn't indicate a defect, just a low quality transformer.

 

[ExDilbert]

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.

That makes no sense since the radio antenna is designed to pick up all radio frequency signals including EMI. You may be confusing EMI shielding with EMI suppression or noise suppression, a feature of some AM radios. Noise suppression is a euphemism for audio clipping or audio limiting that removes the loud peaks in AM audio that are caused by EMI.

 

[BGY11]

Yeah, I doubt that's the issue since if there was inadequate EMI shielding in the head unit, the buzzing noise would be present even without the antenna connected.

I'm going to try two things - a battery, and moving the radio to a friend's place.

I do have one other weird issue though - in one area of my house I get a "pulsing" sound on some FM frequencies. Not like a multipath picket fence thing, but rather a solid pulsing sound every second or so. Again more noticeable on weaker signals.

Maybe I'll just give up and use a portable radio.....

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[s40]

A quick idea, try stacking 8 D cell batteries together and using that to power the radio, and see if the noise goes away (you could walk around to see if there is a louder noise area etc.). Make sure you wire it with the proper grounding though (I think most car radios would be negative ground, but check that out to make sure).

 

[ExDilbert]

The bottom line is that car radios are made to work in a car. I tried something similar with a radio that unplugged from a sleeve in the car to prevent theft. I purchased an extra sleeve and used it with a 12v power supply in the home. It worked OK but the results were not as good as using a regular stereo receiver. Didn't bother with the AM though and haven't for years due to the long standing issues of EMI and lack of fidelity with AM. If I want to listen to an AM station these days, I'll stream it over the internet.

 

[17671]

That makes no sense since the radio antenna is designed to pick up all radio frequency signals including EMI. You may be confusing EMI shielding with EMI suppression or noise suppression, a feature of some AM radios. Noise suppression is a euphemism for audio clipping or audio limiting that removes the loud peaks in AM audio that are caused by EMI.

I may not know the correct terminology but car radios are designed for cars and the volts in your house and the 120 volt power supply do not exist in a car environment so car radios do not necessarily have to be designed and built to block out those signals that are not normally present. So it could be a combination of things from noisy hydro lines, bad voltage switching in the transformer and the radio picking up noise that exists in a house environment but not in a car. Not to mention am antennas are built into the radio not external like fm that also does not help.

 

[BGY11]

Actually, car radios generally use the external antenna for AM as well - otherwise there'd be no difference in reception when the antenna is connected or not.

Either way though, I'm probably going to call it a day with this experiment. Neat idea as I had access to this head unit, but no use trying to fit a square peg in a round whole. Maybe I'll look for a decent home tuner or just use Internet streams for AM (can't really do that with FM since those stations often have contests where the delay in an Internet stream would mean I'd miss out on being the right caller


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[ExDilbert]

Car radios always use the external antenna for AM. That's why I suggested repositioning it by using a longer antenna cable.

 

[17671]

THey may very well use the external antenna for AM, but your typical car antenna port is not the same as it used to be 30 years ago, Car radios also have powered and amplified antennas and if you are using the car radio in side the house are you using the same antenna that came with the car? I remember back in the day volkswagen headunits had amplified antennas so when using a non volkswagen radio in the car ie aftermarket, you would need an adaptor to send power to the antenna for the reception to work properly, and then I found out there are so many different types of antenna connectors some powered, some non, some with diplexers built in to use multiple frequencies like satellite, cellular, etc. its not your grannys car radio anymore, times have changed and then some antennas need to be bonded to a chassis ground for the Am reception to work properly, and when your using it in a house your probably not letting it grounded properly so many things to look at.