The range of my FM transmitter when it is powered from a brand new 9V alkaline battery, its antenna is 80cm long and vertical and is transmitting across a huge river valley with nothing in between is more than 2km to my very sensitive home stereo tuner and my very sensitive car radio.
Its range is down the street about 300m to my cheap Sony Walkman radio set to DISTANT. But then strong local radio stations cause interference. Its range is 30m across the street when the Sony radio is set to LOCAL.
Since it is illegal to use high radio transmitter power then I do not think about it.
Its range is 30m across the street to a cheap clock radio and to a garbage "radio" from The Dollar Store.
After one hour the 9V battery measured 8V and the range was reduced to about half.
