A VSWR (Voltage Standing Wave Ratio) fault indicates an incorrect antenna load which is most commonly caused by a short or open circuit in the Antenna cabling or a fault with the antenna (less common).

The best way to check the exact VSWR values on your system, is to run our proAIS software (supplied free with every AIT250 and AIT1000). Once connected, you should go to the “Diagnostics” tab where the VSWR and RRSI (Received Signal Strength Indicator) figures can be found

RSSI is a percentage figure and so you are looking for figures greater than >50.

The VSWR figures are not percentages but arbitrary measured values and you should get; Forward     >150 (higher the better) Reverse     <30   (lower the better) Causes of problems with antennas are usually coax cable related, so if you have any joins in the cable, please inspect these carefully. If the antenna can be removed from the coax cable (some antennas have a connector in their base), please remove it and do a continuity (and isolation) text of the coax cable.

A: outer plastic sheath B: woven copper shield C: inner dielectric insulator D: copper-plated core

To do the isolation test use a multi-meter set to measure resistance and connect it between the inner and outer. You should normally see very high resistance >20 Million Ohms,  in which case the isolation test has passed. If you see a lower resistance, you could have a defect in the dielectric insulator, corrosion or a partial short somewhere in the cable.

To do the continuity test, again use a multi-meter set to measure resistance and connect it between the inner and outer. Then get someone to short together the inner and outer of the coax at the other end of the cable to where you are measuring. You should see a very low resistance <1 Ohm in which case the continuity test has passed. If you see a higher resistance, you could have a defect in the connector joints, corrosion or a partial break somewhere in the cable.

In some cases, the fault could be caused by a faulty antenna, but hopefully using the tests detailed above, the fault can be traced to a problem in the coax cable or connections which you can rectify without changing the antenna.  

Yes and in fact diligent use of your Class B transceiver is to be encouraged, as the number of pleasure vessels fitting these devices increases. Although the AIS system is technically designed to cope with thousands of vessels, the potential for visual “AIS clutter” on chart plotters is a real problem in congested areas and a “Class B Silent Switch Etiquette” will undoubtedly become necessary. The AIT1000 supports the fitting of a “Silence Switch” which will turn off/on the transmitter so that you can decide when your vessel is seen by other vessels. The AIT1000 continues to receive other vessel positions, when in silent mode and if visibility reduces or you move in to an area with more commercial vessels i.e. crossing a traffic separation zone, you can easily press the Silent Switch again to turn on the transmitter.