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Car's rear defrost being on HELPS reception on AM?

M

Mark from MA

I always assumed anything in my car that is on causes electrical interference which affects my AM reception. The engine being on versus running off the battery is an obvious one for me. Sometimes the power windows will cause some noise.

However, one thing I did notice while driving is that if I turn on the rear defroster, whose traces are right next to my windshield antenna, it actually cuts down on the noise. Now, I've only tested this recently so it has been cold outside everyday but there has not always been frost on the windshield, it's simply turning it on. Any ideas as to what might cause this? It just seems counterintuitive to me.
 
I remember that if you have a ground wave radio signal nulled out inside a house with a radio with a ferrite rod, and turn on a light switch, the radio will often no longer be nulled out and will null out in a slightly different direction. Inside, reradiation from electrical wires add to the incident signal and make it vectorially from another direction. Outside this happens also, with field strength meters when doing proofs and measuring monitoring points, especially in nulls. The 1960 NAB Handbook has an article that mentions this. I would imagine that it is different though in the car. Perhaps the defroster acts like an inductively coupled antenna.
 
I never paid attention to what you guys are discussing, but my turn signals wreak havoc with my AM reception, but only in THIS car.
I do not remember which is on and which is off (I will check it), but the sensitivity goes high-low-high-low-high-low.
A previous vehicle was somewhat affected by the windshield wipers.
This car has a rear window antenna, plus a defogger which seems to have no effect.
None of these things harm the FM reception.
 
The rear defroster on my 2014 Accord has no effect on AM. However, when I'm driving at very slow speeds, turning the steering wheel results in momentary loud noise on AM. I haven't been able to find anyone mentioning this on Honda forums.
 
Perhaps the windshield wipers are the reason why the antennæ are in the rear Windows.
My '73 Chevy Nova had it in the windshield where the wipers were an issue.
 
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