As a continuation of last month’s topic, we will once again present a couple of simple, easy-to-build, circuits that we have used from time to time.
Before proceeding, however, I want to point out some facts about the RF power meter we described last month. You may remember that to calibrate the unit, we applied a 10-volt DC signal to calibrate 1 watt of power at full scale of the meter on the device. A 1-watt CW RF signal is composed of a 20-volt peak-to-peak sine wave voltage or “V”. After it passes through the rectifier”. This must then be further converted to “Vrms” (by multiplying it by the square root of 2 or 0.7071), which now truly represents 1 watt and can be used for conventional power conversions. Therefore the 7.071-volts DC that remains is what actually corresponds to 1 watt (across 50 ohms) and that is what the meter is reading. Note that we did not include the forward diode voltage drop (about 0.25 volts) at this point as it’s low enough to ignore for now.
