# Why would high-voltage transmission cables disturb a car's radio reception?

• I Like Pi
FM radios. So the radio waves from the high voltage line will pass through the FM radio without interference.

## Homework Statement

i was wondering why would high-voltage transmission cables disturb a car's radio reception with static?

## The Attempt at a Solution

Could it be because of the frequency of the voltage? Or something in terms of frequency?

Thanks

The "front end" circuits of radios amplify small signals, which are basically varying electric fields. Because signal strengths can vary depending upon a number of factors in the environment surrounding the radio antenna, they incorporate what is called automatic gain control, or AGC, which varies the amplification of the received signal in order to produce a nearly constant level of signal to the following stages of the radio. Otherwise, the volume of sound that you listen to would irregularly be going loud and soft.

High tension power lines produce an electromagnetic field that surrounds them. If the radio is close by, that field can be so large that even with very selective tuning in the radio's front-end, enough power from that power line signal can get through to the AGC that it thinks there is a very strong radio station signal. It clamps down on the amplification, so the actual radio signal is then "lost" in the background noise that is mostly the 60Hz field from the power wires.

I Like Pi said:

## Homework Statement

i was wondering why would high-voltage transmission cables disturb a car's radio reception with static?

## The Attempt at a Solution

Could it be because of the frequency of the voltage? Or something in terms of frequency?
The frequency is the same as your household 120 VAC: 60 Hz.

High voltage lines should not interfere with radio reception. If it does there is something wrong. High voltage transmission lines require very good insulators. If the insulator should begin to break down sparking can occur. A spark will produce a broad spectrum of radio frequency waves that you will detect with an AM receiver. It should not have much effect on FM radio. You can also get the same effect if you or someone nearby uses power device that produces sparks (eg. a motor with a commutator and brushes).

AM