Why do bridges and powerlines interfere with the reception on AM radio?

Question

Every time I go under a bridge or power lines, the reception on my radio gets fuzzy. I am curious as to the science behind it.

Answer 1

Electricity flowing through wires generates a mild electromagnetic field. When you pass over those power lines, the electromagnetic field is interfering with the radio waves.

Incidentally, those non-contact electrical wire detectors you can buy at stores simply detect the electromagnitism of the wires.

As far as the bridge: it's likely simply a case of the bridge's concrete blocks the radio wave.

Answer 2

Bridges And Powerlines

Answer 3

Am radio waves are pretty long -- around 300 meters is the wavelength. Bridges with metal in them and power lines absorb the signal and it never gets to your radio. Also if there's a power line with a corroded connection, it can create sparks that you can't see that radiate noise. This will usually sound like hum.

Answer 4

Metal structures that are the same sort of length as AM transmissions, around 200m can absorb the radio waves or distort them. Large structures also obstruct the radio waves. Power lines create a very strong alternating field which can disturb AM radio, which is not very good at rejecting this interference.

Answer 5

Am or Fm radio... either one of them are putting out their signal from a radio staton by Radio Frequency waves (actually looks like ocean waves)... AM radio waves are shorter and choppier,less flexible, thus more likely to be banging into something and messin' up the signal! FM radio waves are longer and flowing and less likey to be distrupted! Sometimes a larger anntennea can help the AM signal boost! Sometimes in an older car the outside anntennea can be pulled out farther raised up higher, don't forget to try that first! Good Luck Now! bb