The oscillator output is about 3dBm, which is directly fed to an antenna with a gain of 3dBi, is there any way to estimate how far the signal would be transmitted in free space?
If your system operates in a free space, the above holds. If there is ground, then depending on frequency the propagation may be affected by it, by the ionosphere, by antenna radiation pattern, and more.
The oscillator output is about 3dBm, which is directly fed to an antenna with a gain of 3dBi, is there any way to estimate how far the signal would be transmitted in free space?
use FRIIS EQUATION to determine at a distance the amplitude of the signal , then depending on the receiver sensitivity , the maximum transmission distance is determined