26 January 2011

What is RF Power Meter?

You should be familiar with RF Meter if your job is to service transmitters. Each RF power Meters has it particular frequency and power range to measure specific transmitter. Conversely, it also has features such as plug in where you can adapt a different power and frequency range.  Basically, the RF power meter is specifically design for certain impedance level such as 30, 50 or 75 ohm and connected to the transmitter via coaxial cables.

You can connect the RF meter between the transmitter output and the antenna or dummy load (see fig below) or a power attenuator can be connected a head of the power RF power meter to reduce the power a level within the range of the RF power meter. Most RF power meters measure both forward and reflected power. If the impedance of the antenna or dummy load isn't equal to coaxial cable impedance, not all the power sent down the cable to the antenna will be radiated.

Some of this power will be reflected and travel back (along the coaxial cable) to the transmitter, where it is dissipated as heat in the transmitter circuits (mostly in the final power transistors). Therefore this can cause damage to the transmitter. This however can be avoided since the RF power meter can measure the reflected power from the antenna and immediate action be taken to avoid serious damage to the transmitter.   Some RF power meter have built in dummy load which is a plus since it eliminate the need for extra coaxial cable.

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