1. The problem statement, all variables and given/known data A coaxial transmission line consists of an inner cylindrical conductor of radius 1mm and a cylindrical outer conductor chosen to make the characteristic impedance 75 ohms. The space between the conductors is filled with a gas that can stand a maximum field of 10^5 Vm^-1 without dielectric breakdown. Estimate the maximum mean radio-frequency power that can be transmitted along this line into a matching load. 2. Relevant equations The impedance of a co axial cable is Z=Zo*ln(b/a)/n*2*pi where b is outer radius, a inner radius and n is sqrt(permittivity). 3. The attempt at a solution So for the empty coaxial cable I had Z=Zo*ln(b/a)/2*pi I rearranged this to work out the value of the outer radius which I got as 3.49mm. I used the distance between inner and outer radius and the max electric field to work out potential difference. I then tried to the use the standard P=Vi formula to work out power but my answer is about 8 times too big. I assumed all the power is transmitted due to impedance matching.