AIS650 VSWR Fault Alarm

[chartertom]

This thread is being posted to inquire what could be causing repeated "VSWR fault" alarm messages. This system includes and AIS650 transponder, AIS100 splitter, and Ray70 VHF radio. Also, the AIS receive function has been turned off on the Ray70.

[Chuck - Raymarine - Moderator]

Welcome back to the Raymarine Forum Tom,

The alarm is reporting that the VSWR of the AIS transceiver's VHF antenna / antenna cable assembly is too high ... check the antenna VSWR using the Diagnostics tab for the ProAIS2/ProAIS application or with a VSWR meter. The reported VSWR of the antenna w/extensions should have a VSWR between 1.0:1 - 2.0:1. Please note that a VSWR value will not be reported until the AIS transceiver attempts to transmit ownship data. Should the VSWR of the antenna w/antenna cable assembly exceed this value, then it may indicate a problem with one or more of the antenna cable's couplers, the antenna cable, the antenna, or the AIS650 itself. Should you not have the required equipment to fault isloate the problem, then you may want to seek the assistance of a Certified Raymarine Installer.

Please additionally note that early versions of AIS650 software would sometimes erroneously sense VSWR levels. You can ensure that your AIS650's software is not responsible for this by ensuring that your AIS650 has been updated with the latest available Raymarine product software update.

Should the AIS650's software be up to date and should the VSWR of the antenna / antenna cable assembly not indicate a fault with the antenna / antenna cable assembly, then it would be recommended that the AIS650 be sent to Raymarine’s Product Repair Center to be bench checked / serviced.

[chartertom]

This reply is being sent to convey some results of research on this topic.

It has been discovered that a vhf antenna may work well with a low VSWR at the lower operating frequency of 156MHz for a vhf radio, but may not work well at the higher AIS operation frequency of 162MHz.

After reading your reply to the original post and thinking back to a few occurrences when I was told my vhf radio transmission was poor, I am guessing my VHF antenna has seen its better days.

Understanding this is a shot in the dark that may not resolve this issue, an antenna with the following performance characteristics has been found and will be installed when received:
VSWR: < 2.0:1 = 134-176 MHz (42 MHz)
< 1.5:1 = 146-166 MHz (20MHz)
Gain: Nominal 6dBi
Impedance: 50 ohms

The diagnostics will be performed to determine the current VSWR as suggested in your reply and will be reported.

Once the new antenna is installed the same diagnostics will be performed and the new VSWR will be reported.

[Chuck - Raymarine - Moderator]

You're welcome.

[Oregoncme]

I want to add that an antenna, i.e., an 8' VHF antenna on a collapsable mount, will frequently give the same VSWR fault when the antenna is laid down horizontally atop the roof of a vessel.

[Chuck - Raymarine - Moderator]

Oregoncme,

Your last post is great addition to this thread and would typically be overlooked. Thanks for the suggestion.

[chartertom]

This reply is being made to convey additional findings with the original 8-foot antenna and after installing the new antenna described in my 10 Oct 2017 reply.

An oversight on my part was to include in the original issue definition that the AIS650 software as confirmed to be current as part of its installation.

Regarding further testing of the original antenna; a 3.1:1 VSWR value was displayed when the antenna was connected to the AIS100 splitter using the ProAIS2/ProAIS application.
Further testing with the original antenna directly connected to the AIS650 showed a 4.0:1 VSWR value.

After installing the new antenna described in my 10 Oct 2017 reply; a 1.0:1 VSWR value was displayed.

Although not a on the water test, it is suspected this issue is resolved. It is also suspected the replacement antenna has resolved the poor VHF radio transmission issue.

Prior to this exercise, it was though that all VHF antennas were the same; lessoned learned is that all VHF antennas are not the same.

Another reply will be made when a on the water test is performed.

As always, thanks again for the help!!!

[Chuck - Raymarine - Moderator]

You're welcome.

[chartertom]

This reply is being made to convey results of on water testing of the AIS alarm issue and, secondly, poor VHF radio transmission.

No AIS fault alarm sounded and excellent VHF radio transmission was confirmed via transmission between myself and a warship transiting the Chesapeake Bay.

Issue resolved.

THANKS much!!

[Chuck - Raymarine - Moderator]

You're welcome.