Which instrument is commonly used in the field to verify antenna resonance by measuring SWR?

• A. Spectrum analyzer
• B. Oscilloscope
• C. Multimeter
• D. Portable SWR bridge

Answer: (D)

Measuring SWR in the field is all about how well the antenna is matched to the feedline at the operating frequency. When an antenna is resonant, its impedance is close to the system impedance (typically 50 ohms) and the reactive part is minimal, so little power is reflected back into the transmitter. A portable SWR bridge is built for this exact task: it sits in line between the transmitter and the feedline and separates forward power from reflected power so you can compute the SWR (or VSWR) quickly on a readout. This direct measurement tells you how well the antenna is resonating and whether any tuning is needed.

Other instruments don’t give you this direct, field-ready readout. A spectrum analyzer shows how signal power is distributed across frequencies but doesn’t quantify the forward/reflected power ratio to yield SWR without extra circuitry. An oscilloscope can display RF waveforms but isn’t designed to separate forward and reflected waves for SWR calculation. A multimeter measures DC or basic AC quantities, not the directional RF power needed for SWR. So the portable SWR bridge is the best tool for confirming antenna resonance in the field because it directly indicates how well the antenna is matched at the target frequency.