2026-11-06
VSWR is the most commonly specified figure for a feeder system, and the most commonly misread one: the gap between 1.2 and 1.5 looks like 0.3, but reflected power more than doubles.
Conversion table: VSWR ↔ return loss ↔ reflected power
- VSWR 1.05 → return loss 32 dB → reflected power 0.06%
- VSWR 1.10 → 26 dB → 0.25%
- VSWR 1.15 → 23 dB → 0.5%
- VSWR 1.20 → 21 dB → 0.8%
- VSWR 1.30 → 17.7 dB → 1.7%
- VSWR 1.50 → 14 dB → 4.0%
- VSWR 2.00 → 9.5 dB → 11%
Most base station projects require assembled jumpers at VSWR ≤ 1.15 and the full chain at ≤ 1.3. Past 1.5, four percent of transmit power is reflected — coverage suffers and the power amp runs hotter, tripping protection sooner.
A seven-point field checklist for failed VSWR
- Connector torque: N-type and 7/16 DIN both have torque specs; hand-tight joints are the number-one cause.
- Centre-conductor burrs: left by field cutting tools; inspect with a magnifier — they cause intermittent arcing.
- Bend radius: a one-time bend tighter than 10× OD changes conductor spacing and shifts VSWR with frequency.
- Water ingress: aged or wrongly-wrapped tape lets rain travel down the cable; VSWR visibly worsens after rain.
- Crush damage: over-tightened fixing clips or scaffold pressure create a local impedance mismatch.
- Jumper length: at some frequencies a jumper is exactly the wrong electrical length; swapping 0.5 m for 1 m often helps.
- Instrument calibration: an uncalibrated test lead makes the analyser's error look like the cable's fault.
Work down the list and most VSWR failures are solved on site; what remains is usually internal cable damage that needs a section replaced.