location of RF source

I want to know that are there any methods to calculate distance of an RF source like for e.g if there is an FM transmitter can I calculate that how much distance is it away from my location and in which direction .

Theoreticaly you can find the distance of a transmitter (knowing the transmitted power, the link budget, antennas gain, the propagation losses, multipath, etc).
...but practically is almost impossible to do this distance calculation just receiving a signal.
Finding the location of the transmitter is relative simple, using a receive directive antenna.

RF source location is best done by triangulation, with a receiver and a directional antenna.
If the source is a FM transmitter, the receiver should have RSSI (signal level) indication, to find the direction (azimuth) from one location, then move the setup to another location and repeat. The RF source will be where both azimuth lines cross.
Depending upon the terrain structure, the triangulation procedure should be repeated from more than two locations.
A recommended reading is the ARRL Radio Amateur's Handbook where more details are given.

The initial post didn't specify that the FM source is not moving. What happen if the TX source is moving when you are moving to find the azimuth?
For a moving TX source you need 3 synchronized receivers, which complicate things a lot.
There is another option used in GSM, where the system knows exactly the distance between mobile and the base station. There is a time delay that appear between mobile and BS communication, delay that is translated in distance. This delay is compensated by the system using an option named Timing Advanced.

Hi all,

I like most when a cute girl or boy like you starts changing the initial conditions!

It is true that the situation in GSM and generally in cell network is just reverse. You have a network of base stations, so you can use the time delay to find the emitter. If you only have two base stations capable to communicate with a moving emitter, the triangulation gives only one line and two ambiguous positions. You need more than two base stations to locate the emitter correctly.

To locate any signal source (modulation not important) you can buy a system with 4-8 or more scanning vertical GP antennas, to get an immediate azimuth.
Then you can use two such systems to locate any, moving or fixed emitter.

Cute or not, should be a difference if there is a boy or a girl changing the initial condition...at least for me, is important...