Return Loss is a measure (in decibels) of how much signal is reflected by a mismatch in your RF system. It is derived from the Voltage Standing Wave Ratio (VSWR) and expresses how well your load is matched to the transmission line.

The formula used is: \[ \text{Return Loss (dB)} = -20 \cdot \log_{10} \left( \frac{\text{VSWR} - 1}{\text{VSWR} + 1} \right) \]

A higher return loss indicates better matching and less reflected power. For example:

• VSWR = 1.5 → Return Loss ≈ 14 dB
• VSWR = 2.0 → Return Loss ≈ 9.5 dB
• VSWR = 3.0 → Return Loss ≈ 6 dB

Most modern transmitters prefer a return loss of at least 10 dB (VSWR ≤ 2:1) for safe and efficient operation.