Amplitude of Radio Waves?

Question

Just interested in what the general amplitude of Radio Waves are. I'm studying it in Physics now, and it says that the wavelength is about 1KM but doesn't mention the amplitude. If anybody could tell me for AM and FM, I'd be very grateful.

Thanks to anyone who answers.

Answer 1

First off, you may want to refer to:

http://www.1728.com/freqwave.htm

This will give you the back formulas to convert from wavelength to frequency and vice versa.

A wavelength of 1Km has a frequency of approx. 300 kHz or 0.3 MHz which is rather low and is the bottom edge of of the Medium Wave (MW) band which stretches from  0.3 to 3 MHz. In the middle of this band is found AM radio which runs from about 0.5 to 1.6 MHz. Band properties, communications wise, is rather short range during daylight hours an surprisingly long range at night, sometime out to 1500 miles.

Just above this band is the High Frequency (HF) band which stretches from 3.0 to 30 MHz and is also called short wave.

Amplitude of a waveform is a function of power. A higher power transmitter will create a higher amplitude signal at the source. You would expect a 1000 watt transmitter to put out a larger amplitude signal than a 100 watt transmitter. As you can probably guess the 1KW signal will travel further and sound louder at any particular distance from the transmitting site when using the AM mode of operation.

  

Answer 2

Electromagnetic waves do not have an "amplitude" in the traditional sense (like the amplitude of waves in the ocean).  The "amplitude" of radio and other EM waves is measured as the strength of the electromagnetic field in which the waves exist.

Therefore, there's no "constant" amplitude for radio waves. It depends on the field strength of your radio transmitter.

If you think of it in terms of quanta, a single radio photon does not have an amplitude at all, but it does have a frequency. The "amplitude" comes from how many photons are present with a similar frequency.