Tools you might need next
Calculate half-wave dipole and quarter-wave vertical antenna element length from frequency. Includes velocity factor correction for wire type.
Calculate coaxial cable RF signal loss in dB from cable type, run length, and frequency. Estimate transmit power delivered to your antenna.
Convert RF power between watts, dBm, and dBW. Calculate power density and link budget components for ham radio and wireless.
Use square roots of forward and reflected power readings. SWR of 1:1 is perfect match; 1.5:1 or below is acceptable for most transceivers.
SWR = (√P_fwd + √P_ref) ÷ (√P_fwd − √P_ref)Return loss expresses mismatch in dB. Higher return loss (more negative) is better. 20 dB RL ≈ 1.22:1 SWR.
RL (dB) = −10 × log10(P_ref ÷ P_fwd)At 1.5:1 SWR with 100W forward, roughly 4% (4W) reflects. Modern transceivers fold back power above ~2:1 SWR.
Reflected % = (P_ref ÷ P_fwd) × 100Updated: July 2026
SWR calculates to approximately 1.33:1 — acceptable match for HF operation without tuner.
50W forward, 12.5W reflected yields SWR ~3:1 — investigate connector, antenna length, or mount ground before transmitting.
Multi-band antenna showing 1.2:1 on 20m but 2.5:1 on 15m — tuner recommended for 15m operation or adjust antenna for broader bandwidth.
Standing Wave Ratio (SWR) indicates antenna system impedance match. Enter forward and reflected power from your wattmeter to calculate SWR, return loss in dB, and percentage of power reflected back to the transmitter.