General Rule of Thumb between Watts and Transmission Distance?
Is there a general rule of thumb between the amount of watts pumped into a radio transmission and the distance somebody is able to receive it?
For Instance, I believe a 4/Watt CB Radio can transmit 10 miles if the line of sight is clear. Does that mean 4/Watts = 10/Miles? So 40/Watts = 100/Miles?
The relationship between radiated power and signal strength over distance is Logarithmic. Signal strength over distance decreases at a logarithmic rate. Therefore, to increase signal strength over distance, you need to increase power at a logarithmic rate.
For example, if you measured signal strength from a transmitter at 10 miles and another measurement at 20 miles, the signal strength at 20 miles will be ~ 1/4 the signal strength it is at 10 miles. Thus, in order to maintain the same signal strength at 20 miles you got at 10 miles, you would need to crank up the transmitter power by 4 times.
So, to answer your question. If you want to ~ double the range of a 4 watt transmitter, then that transmitter will need to increase 4 times. Thus, you will need 16 Watts power to get the same signal strength at 20 miles as you had at 10 miles.
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