How high is RF voltage at ends of dipole antenna running 100W?

While learning the basics of inverted V dipole antenna, we are asked to keep the ends of the antenna out of reach for humans and animals. The reason is that the antenna RF voltage is highest at its ends for a dipole. Direct contact with a live antenna can cause difficult to heal RF burns. We will look at a simple calculation of approximate voltage of a dipole antenna with impedance of around 73Ω, running 100W power from the radio. Feedpoint impedance of inverted V may be lower at about 50Ω. RF voltage at the feed point will be lowest. For resonant dipole antenna, the impedance at the ends will be high, of the order of 4000Ω, similar to the feed point impedance of an end fed half-wave dipole antenna.

We know that P = (V_RMS)²/Z, where P is the power, V_RMS the root mean square voltage and Z the impedance. Rearranging, we get V_RMS = √(P*Z) = √(100W * 73Ω) = 85.44V, at the feed point with impedance 73Ω. Peak voltage at the feed point will be 85.44V * √2 = 120.8V.

If the impedance at the tip of the dipole antenna is 4000Ω:

V_Peak = √(P*Z) * √2 = √(100W * 4000Ω) * √2 = 632.46 * √2 = 894.4 V

Now you can get an idea about the importance of keeping the ends of the dipole well insulated and out of reach of human beings and animals! This calculation is based on the situation at 1:1 VSWR and presumed impedance of dipole at the end of 4000Ω, though it may vary from 1800Ω to 5000Ω.