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The Toolbox — Troubleshooting

RF & Antenna Systems

Symptom-based diagnostic guides for coax feedline faults and GPS/navigation receivers.

Coax Feedline

High SWR with antenna that previously worked

Possible Causes

  • •Water in connector
  • •Cracked or kinked coax
  • •Connector pulled partially off
  • •Center conductor broken internally

Diagnostic Steps

  1. 1.Inspect all connectors for moisture and corrosion
  2. 2.Flex coax along its length while monitoring SWR meter — change in SWR indicates internal break
  3. 3.Disconnect antenna and measure impedance of feedline looking into open end
  4. 4.Replace suspect section of feedline

Cable feels warm after transmitting

Possible Causes

  • •High SWR causing high reflected power
  • •Excessive power for cable rating
  • •Poor connector causing arcing
  • •Damaged dielectric

Diagnostic Steps

  1. 1.Check SWR and reduce transmit power if high
  2. 2.Verify cable is rated for transmit power level
  3. 3.Inspect connectors for burn marks or carbon deposits
  4. 4.Replace cable if dielectric is discolored or damaged

Noise on receive only in certain antenna orientations

Possible Causes

  • •Shield continuity problem
  • •Broken braid strands in connector
  • •Loose center conductor
  • •Poor weatherproofing allowing moisture

Diagnostic Steps

  1. 1.Rotate antenna and note if noise changes with orientation
  2. 2.Inspect connector braid for broken strands or incomplete coverage
  3. 3.Check center conductor for solid connection in connector body
  4. 4.Re-weatherproof all outdoor connectors with self-amalgamating tape

GPS / Navigation Receiver

No position fix / searching for satellites

Possible Causes

  • •Poor antenna placement
  • •Antenna obstruction
  • •Damaged antenna cable
  • •Cold start after long storage

Diagnostic Steps

  1. 1.Ensure antenna has clear 360-degree view of sky
  2. 2.Check antenna cable for damage or tight bends
  3. 3.Allow up to 15 minutes for initial cold start fix
  4. 4.Verify antenna is active type and receiving power from receiver

Position drifting or inaccurate

Possible Causes

  • •High HDOP due to poor satellite geometry
  • •Multipath reflections
  • •Antenna near metal structures
  • •Interference from other electronics

Diagnostic Steps

  1. 1.Check satellite count and HDOP on receiver display
  2. 2.Relocate antenna away from radar domes, masts, and metal surfaces
  3. 3.Check for interference from VHF transmissions
  4. 4.Compare position to known landmark or chart

NMEA sentences not received by chartplotter

Possible Causes

  • •Incorrect baud rate
  • •Wiring error
  • •Wrong NMEA sentence type enabled
  • •Ground loop

Diagnostic Steps

  1. 1.Verify baud rate matches between GPS and chartplotter — default is 4800 baud for NMEA 0183
  2. 2.Check TX from GPS connects to RX on chartplotter
  3. 3.Verify GGA and RMC sentences are enabled in GPS output settings
  4. 4.Use differential wiring (RS-422) to eliminate ground loops on long cable runs