Is it possible to control distance of RF Transmitter

Question

Noob question here, is it possible to control the distance range of RF transmitter.

I need a RF transmitter application where i can control its distance with pot.

Answer 1

In the strict sense, no. Once EM waves leave the nearby vicinity of the antenna, they irreversibly propagate thru space forever or until they hit something. Nothing you can do at the transmitter can stop them.

However, every receiver needs some minimum signal strength to receive a signal properly, and the power density (watts per square meter) goes down with the square of the distance from the transmitter. Between these two, you can, in theory, adjust the transmitter power so that a particular receiver needs to be within some minimum distance to properly receive the transmission.

However, a lot of things mess this up in practice to the point where its only useful in a broad sense. Power density goes down with the square to the distance in free space. Two points on the surface of the earth don't have just free space between them. There are various things that the EM wave can bounce off of, be absorbed by, and be diffracted by. Bounces and diffractions arriving from different directions can interfere with each other both destructively and constructively.

Receivers and their antennas are all not created equal either. The directionality of a antenna makes a huge difference to any one received signal, and the circuit inside every receiver doesn't just magically pick up the transmission above the same minimum threshold.

All these facts combine to not give you a very predictable and sharp "edge" to a transmission.