Ever wonder how much power is loss in your coax cable feedline? Here is a website which helps you estimate power loss in your antenna feedline according to your choice of coax cable.
For example :
If you are transmitting on 145 MHz frequency with 65 Watt of power using 15 meter RG-58 cable, the maximum effective power radiated by your antenna is just about half of the transmitting power (36.156 MHz).
But when you switch to RG-8 cable, the loss would be significantly lower, and your antenna would radiate 54 Watt of power.
Since the power loss is significant, it is advisable that you consider the choice of your feedline before setting up your station. In emergency or QRP situation, every 1 Watt counts.
If you have no other choice other than to use RG-58 cable, it is advisable to put your antenna as high as possible with the shortest amount of cable possible. This will save your rig a lot of hard work, and may actually get your signal to travel further than before
How much power loss in your feedline ? Check it at Coax Cable and Line Loss Calculator website