Also known as: standing wave ratio, SWR, VSWR

Standing wave ratio (SWR, often VSWR) measures how well an antenna is impedance-matched to its feedline and radio at a given frequency.¹ A perfect match is 1:1.

SWR measures how well the antenna is matched; a poor match reflects energy back instead of radiating it.

How it works

When the match is poor, some energy is reflected back rather than transferred, creating standing waves on the feedline. For transmitting this can damage equipment; for receive-only SDR use it mainly costs a little signal.

Relevance to SDR

A reasonably matched, resonant antenna delivers more signal to the SDR than a mismatched one, helping SNR.

Sources

1. Standing wave ratio — Wikipedia, on impedance matching, reflected power, and VSWR. ↩

See also

• Antenna
• Dipole antenna
• Attenuation

Learn it step by step

• Antennas 101