The power of a signal of complex shape or high frequency cannot be measured with a wattmeter. Meanwhile, when setting up power amplifiers and transmitters, this is often required. Indirect measurement methods come to the rescue.
Necessary
- - diodes;
- - one-shot K155AG1 or other;
- - resistors and capacitors;
- - voltmeter;
- - probes;
- - soldering iron;
- - solder;
- - neutral flux.
Instructions
Step 1
Use an incandescent lamp to load the power amplifier or transmitter. In a heated state, it should consume approximately the same power as the load (respectively, a dynamic head or antenna). Connect a lamp to the output of the device whose output you want to measure, and then place it in an opaque tube so that no extraneous lighting affects the measurement results. If the tube is made of metal, take measures to prevent short circuits.
Step 2
On the opposite side, place the desired type of photocell in the same tube. Connect it to the measuring device in the most suitable way for this. For example, connect a photoresistor or phototransistor to a milliammeter through a power source, and a photodiode directly, without using such a source.
Step 3
Apply a signal of known amplitude to the input of an amplifier or transmitter. The lamp inside the tube will light up, illuminating the photocell, and the arrow of the measuring device will deflect. Remember his readings.
Step 4
Now turn off the amplifier or transmitter, disconnect the lamp from it, and then connect it to a constant voltage source through an ammeter. Connect a voltmeter parallel to the lamp. Set the output voltage of the power supply so that the device connected to the photocell shows the same result as in the previous case.
Step 5
Now read the readings of the voltmeter and ammeter, convert them to the SI system, and then multiply by each other. You will get the power the light is currently using. Exactly the same signal strength was generated in the previous experiment by your amplifier or transmitter.
Step 6
If you do not have a photocell, but there are two identical bulbs, they can be placed side by side, and a signal from an amplifier or transmitter can be applied to one of them, and from a power source to the other. By adjusting the output voltage of the latter, ensure that both lamps glow with the same intensity, then read the readings of the voltmeter and ammeter and calculate the power as described above.
