[TG] [TG11] AIS 500 fault message while transmitting on VHF

[Tom - Raymarine - Moderator]

Hello Berwick,

If the AIS and VHF are both trying to transmit at once, the VHF wins (the internal splitter favours the VHF for safety reasons), which is I'm pretty sure why you're sometimes seeing the Tx errors when transmitting on the VHF. To avoid this you'd need to use separate antennas.

Re. the high VSWR warning: I am pretty sure your antenna VSWR is not really 1:1, especially not across the whole frequency band. That's unrealistically low (1:1 is the ideal, zero-loss situation), so I think that either your meter is leading you astray or transmission line loss in your cabling is masking a much higher VSWR (see continuouswave's excellent explanation of this here.) The screenshots of ProAIS you've posted show normal Tx Forward Power (transmitted by the AIS) but high Tx Reflected Power (what's reflected back from the antenna to the AIS.) The Reflected Power should be <10, whereas your images show 57 and 156(!). I think that your VSWR measurement is incorrect and that you actually have (probably) a poor and intermittent contact in your antenna cabling which is giving high to very high VSWR in fact.

Regards,
Tom