Mycal's Power Meter Plans

Power Meter/Dummy Load

Two very handy items to have when you are building and/or adjusting your radio transmitter are the Power Meter and the Dummy Load. A Power Meter for adjusting your transmitter for maximum power output and a Dummy Load to appear as a perfect antenna and absorb the RF signal without radiating a signal. You may transmit all day long at any power level legally as long is it is into a suitable Dummy Load.

By integrating a power meter and a dummy load you will get very accurate readings of your power output. You must have a high-impedance Voltage Ohm Meter to get accurate readings with the power meter shown here. A 20M ohm meter will work well.

The following is the schematic for the combination Power Meter/Dummy load. You may use 1/4, 1/2, 1, or 2 watt carbon resistors for R2 through R5. Using 1/4 watt resistors the Dummy Load will be able to handle up to a watt of output power for long periods of time and 2, 3 and up to 4 watts for shorter periods of time. By using larger load carring resistors you can expand the amount a power the Dummy Load will handle without burning up.

Parts List
D1 - 1n4148     C1 - 47pf       C2 - .1uf
R1 - 22K           R2,R3,R4,R5 - 200 ohms

To calculate the power output of your transmitter while using this device use the following formula:

Power Output in Watts = (V*V) / 50

Example if you measure 2 volts on your voltage meter you output power would be:

Power Output = (2*2)/50 = 4/50 = .08 watts = 80mw

This Power Meter/Dummy Load is a perfect addition to any DIY micro power radio station.