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.
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
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.
Last Updated October 31, 1995.
©1995 Mycal, All Rights Reserved