VSWR in Plain English: Pre-Go-Live Checks

Why VSWR matters more than gain

Installers spend a lot of time looking at gain figures on datasheets. In practice, the number that most reliably predicts whether an antenna system will behave itself in the field is Voltage Standing Wave Ratio (VSWR). If the VSWR is wrong, no amount of gain will save the install.

VSWR is a measure of how efficiently RF power moves from your transmitter, down the feeder, into the antenna, and out into free space. When the impedance of every stage is matched (almost always 50 ohms in our world), power transfers cleanly and VSWR is close to 1:1. When something is mismatched, power reflects back down the cable and VSWR climbs.

What good looks like

As a rough industry rule of thumb, installers work to the following VSWR targets across the working band:

• 1.5:1 or better: a good match. The target for most professional VHF, UHF and cellular installations.
• 1.5:1 to 2:1: acceptable on many systems, but worth investigating on a new install.
• Above 2:1: something is wrong. Find the cause before handover.

Five checks worth running before you sign off

1. Sweep the whole band, not one frequency. Check VSWR at the bottom, centre and top of the channels the system will actually use.
2. Inspect every connector. Most poor readings trace back to a badly terminated, loose or wet connector.
3. Check the cable run. Look for crushed sections, tight bends and damaged jackets, and confirm the cable type matches the specification.
4. Confirm the mount and ground plane. A poorly bonded mount or missing ground plane will raise VSWR on otherwise good hardware.
5. Record the result. Save the sweep as the commissioning baseline so future maintenance visits have something to compare against.

A note on return loss

VSWR and return loss are two ways of expressing the same thing. A 1.5:1 VSWR is roughly equivalent to 14 dB return loss. If your test kit reports one and your datasheet the other, a quick conversion table on your phone saves time on site.

When to call the manufacturer

If you have checked the connectors, the cable and the mount, and you are still seeing a VSWR issue that tracks with the antenna itself, it is time to talk to the manufacturer. We would rather hear from you on day one than find out in a year's time that the unit has been working hard in a corner it should never have been asked to sit in.

Need a quick sanity-check on a specific model? Email our engineering team or request a datasheet from any product page.

Related products

• MAST/WALL MOUNT UNIVERSAL
• MAST/RAIL MOUNT SS 1"-14NF
• ADAPTER VHF23/33/63 DELRIN 1"-14NF

Related reading

• Measuring VSWR and Return Loss: Installer Guide
• Coaxial Cable Selection for Antenna Systems
• Connectors and Cabling for UHF Base Stations