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Docs Radio & RF Design Antenna Troubleshooting

Antenna Troubleshooting

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The antenna fault checklist: broken coax, bad connectors, detuning, and the test sequence that isolates the problem.

Antenna Troubleshooting

Antenna faults are the most common cause of “the beacon transmits but nobody hears it”. The checklist is short, and the tests are simple.

The symptom list

SymptomLikely cause
Range much shorter than beforeDamaged coax or connector
Range short from day oneWrong antenna for the band, or no ground plane
SWR high on one channel onlyNarrow-band antenna, wrong tuning
SWR varies when you touch itBad connector or ground connection
Sudden total failureAntenna snapped at the base

The test sequence

  1. Visual: inspect the coax for kinks, the connector for corrosion, the whip for cracks.
  2. Multimeter: continuity center-to-center, shield-to-shield; NO continuity center-to-shield.
  3. SWR: measure across the whole band (see VSWR Measurement).
  4. Range test: the two-beacon test against a known-good antenna (see Two Beacon Bench Test).

The classic mistakes

MistakeWhy it fails
RP-SMA antenna on SMA mountDoes not mate properly
2.4 GHz WiFi antennaWrong band entirely
Whip without ground planeNo return path (see Quarter Wave Antenna)
Coax pinched in the case seamShort or broken center conductor
Metal battery against the antennaDetuning (see Antenna Mounting)

The wet antenna

Water in a connector adds loss and corrosion. After any wet trip: dry the connector, check the SWR again, and treat a slowly rising SWR over weeks as water ingress, not mystery.