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There are many things other than the antenna that can cause high SWR. SWR meter readings take into consideration the
antenna, the coaxial cable, the mount, the mounting location, the vehicle and objects in the antennas near-field environment.
We broke our list of common high SWR causes into six primary categories. The order of the categories does not imply that one
is more common than the other, however, the list within each category is arranged based upon our experience and shows the
most common causes higher on the list than the lesser common causes. Get to know the basics of SWR by reading the article
"What is SWR?".
ANTENNA RELATED
- Antenna was not tuned in its final mounting location
- Antenna tip installed AFTER the antenna was tuned
- Testing or tuning with doors, hood or trunk open (altered ground plane)
- Antenna not mounted vertically
- Incompatibility between antenna and vehicle for undetermined reasons
- Insufficient tuning range due to antenna/installation incompatibility
- Antenna tested/tuned inside garage, carport, etc.
- Antenna was tuned then moved to another mounting location or vehicle>
- Ground plane and no-ground plane antennas used with wrong coax cable type
- Antenna grounded to vehicle chassis ground circuit
- Internal antenna issue (verify base to tip continuity)
- Antenna not designed for use with CB radio
ANTENNA MOUNT
- Ungrounded mount (re: ground plane dependent antenna system only)
- Relying on a chassis ground via the radio (must test with coax off of radio)
- Anodized or powder coated mounts (insulated from chassis ground)
- Antenna stud mount improperly installed (shorted)
- Coax shield side not grounding to mount (re: ground plane dependent antenna system only)
- Improper positioning of required insulators on antenna stud
COAXIAL CABLE
- Open (broken) center conductor or shield
- Center conductor to shield short (undesirable connection)
- Severe pinches, sharp bends, and/or cuts in outer jacket of coax
- Excess coax rolled into a coil for stowing.
- Low quality coax cable
- Antenna/Counterpoise anomolies and potential coax cable resonance
- Wrong type of coax (Use ONLY 50-ohm for single antennas, 75-ohm for duals)
- Using a standard antenna with a no-ground-plane cable assembly or vice versa
MOUNTING LOCATION
- Antenna running parallel to reflective surface over too much of its length (and too close)
- Antenna mount affixed to an ungrounded in-bed pickup toolbox
- Antenna mount affixed to insulated roof rack (anodized or powder coated)
- Antenna mount affixed to an ungrounded spare tire swing arm
- Antenna mounted too close to other antennas (24" minimum recommended)
- Less than 60% of a top loaded antenna in free air-space
- Dual antennas not having unobstructed line-of-sight between top 60% of length
GROUND PLANE (COUNTERPOISE)
- Vehicle is a composite material (fiberglass) - NGP system required.
- Insufficient ground plane size (motorcycles, ATV's, etc)
- Running too long of a wire from mount to chassis to ground the mount
- Thin sheet aluminum vehicle shell (insufficient metal mass)
- Antenna positioned in a manner that doesn't allow it to use available metal counterpoise
SWR METER
- "To Transmitter" and "To Antenna" coax leads reversed
- Failure to recalibrate SWR meter after every channel change
- Calibrating meter when in SWR/Ref mode instead of Cal/Fwd mode
- Innaccurate, defective or uncalibrated SWR meter
- Unable to calibrate meter to set line (radio output power issue)
- Improper testing procedure
- Faulty coaxial jumper between radio and SWR meter
CB RADIO
- Defective/damaged transceiver (radio)
- Insufficient current to transmitter is limiting output
- High resistance 12v power connection
- Partially broken wire on either positive or negative 12v lead
- Loose connection on either positive of negative 12v lead
- Corroded power lead on either positive or negative 12v wire
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