T4C: Meters and their placement in circuits, peak-reading and RF watt; ratings of fuses and switches

A multimeter would normally be used to measure voltage, current and resistance.

A voltmeter is usually connected in parallel with the circuit under test.

An ammeter is usually connected in series with the circuit under test.

If you switch a multimeter to measure resistance while you have it connected to measure voltage it would probably destroy the meter circuitry.

If you switch a multimeter to read microamps and connect it into a circuit drawing 5 amps, it would probably destroy the meter circuitry.


A directional wattmeter measures forward and reflected power.

Most RF watt meters usually operate at a line impedance of 50 ohms.

An RF wattmeter should be connected at the transmitter output connector for the most accurate readings of transmitter output power.

If a directional RF wattmeter reads 90 watts forward power and 10 watts reflected power, the actual transmitter output power is 80 watts.

You might use a peak-reading RF wattmeter at your station to make sure your transmitter's output power is not higher than that authorized by your license class.


If you replace its blown 5 amp AC line fuse with a 30 amp fuse in your transceiver, it could use more current than 5 amps and a fire could occur.