Which instrument can be used to determine SWR?

A directional wattmeter is specifically designed to measure the power flowing in a transmission line, allowing users to ascertain how much power is being reflected back to the source. This capability is crucial for determining the Standing Wave Ratio (SWR), a key parameter that indicates the efficiency of the antenna system. SWR is calculated by measuring the forward and reflected power, which the directional wattmeter can provide. This measurement helps operators understand whether the impedance of the antenna is properly matched to the transmitter, ensuring optimal performance.

In contrast, a voltmeter measures voltage levels in circuits, which does not directly relate to the measurement of power or reflection in transmission lines. An ohmmeter is used to measure resistance and is also not relevant for determining power flow or SWR. Lastly, an iambic pentameter refers to a metrical pattern in poetry and is unrelated to electrical measurements. Thus, the directional wattmeter stands out as the appropriate instrument for this task.