Signals Help

Thread Starter


Joined Mar 17, 2008
i wanted to know what is the
1. max range (distance ) and frequencies of AM signals
2. max range (distance ) and frequencies of FM signals


Joined Jul 17, 2007
Are you talking for earthbound transmitting/receiving stations?

If so, transmitted AM signals can be heard thousands of miles away. FM signals are generally limited to line-of-sight.

The upper end of the RF frequency range is limited by the lower end of the infrared spectrum.

As far as the range of transmitters built by humans - I beleive we're still in communications with the spacecraft Voyager I, which left the solar system a few years ago. It was launched over 30 years ago.
We've been receiving RF signals from quasars (they may appear like stars, but they are not) from hundreds of light-years away. The power output from these quasars are many times that of our entire galaxy.


Joined May 19, 2004
and, heavily dependent on the transmitter and receiver antenna design and size, atmospheric conditions, as well as transmitting amp power output. i am not sure we have totally realized the actual physical limitations of either.


Joined Dec 20, 2007
AM or FM is the type of modulation. It has nothing to do with distance.

Distance is affected by the frequency. AM broadcast band radio uses a low frequency that bounces off the ionosphere at night. FM broadcast band radio uses a very high frequency that does not bounce so its range is limited by the line of sight. The earth curves and blocks the transmission.

Aircraft communications radios use very high frequency AM that does not go far.