Back in 2020, I posted about the alarm sentences for the B600s AIS transceiver by Alltek Marine. While on the boat this weekend, I was monitoring the NMEA sentences while testing some new software, and I noticed that the sentences were still showing up, and the AMEC app on the tablet was also saying “Error”. I dropped Alltek an email, asking about the sentences, as the manual I have doesn’t provide any clarity on the values in the sentences.

I received an answer in less than 24 hours, and it clarified that the sentence I was seeing – – is an inactive alarm sentence. A screenshot was included, which I’ve reproduced in text in the vain hope that search engines will pick it up.

The status of an alarm can be identified by two letters in the alarm sentence, “A” and “V”. The alarm sentence is constructed as: $AIALR,hhmmss.ss,xxx,A,A,c-c, where:

hhmmss.ss = Time (UTC) of alarm condition change
xxx = Unique alarm identifier
A = Alarm condition (A = active, V = inactive)
A = Alarm’s acknowledge state, A = acknowledged, V = unacknowledged
c-c = Alarm’s description text

So if the pair of letters is V,A, or V,V, the alarm is inactive. If it’s A,A then it’s active and acknowledged, and if it’s A,V then it’s active and unacknowledged.

The sentence that I was concerned about was $AIALR,246060.00,002,V,V,AIS: Antenna VSWR exceeds limit*43 – VSWR being exceeded could damage the transmitter. The timestamp is also a bit odd, but looking in my logs, I see a $AIALR,100615.00,002,V,V,AIS: Antenna VSWR exceeds limit*46 message shortly afterwards, so 246060 is probably a “time is not in sync” clock value. I’m going to borrow a SWR meter anyway, just to get a baseline measure of my feeder to the antenna, since there’s a join in the middle. It won’t be as accurate as it could be if I had a dummy load at the end of the cable, but I can live with that.

AIS alarm sentences redux
Tagged on: