Advantage of Class B+ AIS on a sailboat?

[FlyingScot]

If buying today, it seems simple enough to spend a little extra and get the B+.
I'm not sure I would upgrade a fully functional B transceiver.
We have a Digital Yacht 5000 that has a built in antenna splitter. Until I replace the VHF cable up the mast I won't comment on it's capabilities.
They do have a Windows based software that I run on my laptop to check VSWR which currently sits @ 1.9:1. Not as good as I want it to be.

[DreamWeaver III]

I have recently been called to several boats that have had low range on both AIS and VHF RX and TX. In all cases the coax was the issue having become lossy due to age and or water ingress / corrosion - anything over ten years is going to compromise your received and transmit range. In all cases the coax in question was your typical 1/4inch RG58 witch when new had at best about 7dB loss. The coax is absorbing about so much signal that only about 9.5W out of 50W from VHF is getting to your antenna! (assumed length 30m) this compared to our go-to replacement LMR400 with 1.5dB loss where 34W actually gets to the antenna. Of course the same attenuation happens in receive too. All of the owners of the yachts were amazed at the improvement in performance in both TX and RX for VHF and AIS - one was so bad that type-B transponder range was down to less than 6 miles - this improved to over 28 mile. Food for thought

[PPLepew]

I have AIS on the plotter in front of me, using a VHF antenna on top of 60' (above water) mast with a splitter down by the VHF/AIS boxes (Vesper Marine).

My MAIN advantage is that I set a 15 min vector line on all vessels seen, including mine (40' sailing cat). And only have to see where they cross mine and give me an instant picture of my surroundings. No more guessing, it's all in front of me.

[Jim Cate]

this compared to our go-to replacement LMR400 with 1.5dB loss where 34W actually gets to the antenna.

Now this is truly amazing co-ax! Must be some sort of amplifier to get 34 watts to the antenna when marine VHF transmitters are limited to 25 watts output.

jim

[Cpt Pat]

Originally Posted by DreamWeaver III

I have recently been called to several boats that have had low range on both AIS and VHF RX and TX. In all cases the coax was the issue having become lossy due to age and or water ingress / corrosion - anything over ten years is going to compromise your received and transmit range. In all cases the coax in question was your typical 1/4inch RG58 witch when new had at best about 7dB loss. The coax is absorbing about so much signal that only about 9.5W out of 50W from VHF is getting to your antenna! (assumed length 30m) this compared to our go-to replacement LMR400 with 1.5dB loss where 34W actually gets to the antenna. Of course the same attenuation happens in receive too. All of the owners of the yachts were amazed at the improvement in performance in both TX and RX for VHF and AIS - one was so bad that type-B transponder range was down to less than 6 miles - this improved to over 28 mile. Food for thought

I'm an FCC licensed GMDSS Maintainer. My experience duplicates yours. Also: the "solderless" PL-259 connectors supplied with some antennas are pure junk. PL-259 connectors aren't waterproof, and when combined with a "solderless" assembly configuration depending on a pristine uncorrorded internal pressure connection -- you will be lucky if it lasts any time at all. If you can't solder-on a proper connector and apply a waterproof butyl covering - find someone who can.

I have read some reports that the foam insulation in LMR coax cable absorbs water over time that then migrates through the cable, drastically increasing its attenuation over time. I can't confirm that finding, but I imagine it's only a factor when proper waterproofing of both ends of the cable was not applied.

[DreamWeaver III]

Originally Posted by Cpt Pat

I'm an FCC licensed GMDSS Maintainer. My experience duplicates yours. Also: the "solderless" PL-259 connectors supplied with some antennas are pure junk. PL-259 connectors aren't waterproof, and when combined with a "solderless" assembly configuration depending on a pristine uncorrorded internal pressure connection -- you will be lucky if it lasts any time at all. If you can't solder-on a proper connector and apply a waterproof butyl covering - find someone who can.

I have read some reports that the foam insulation in LMR coax cable absorbs water over time that then migrates through the cable, drastically increasing its attenuation over time. I can't confirm that finding, but I imagine it's only a factor when proper waterproofing of both ends of the cable was not applied.

I have never had an issue with the foam absorbing moisture, that said we use the direct burial variant of LMR400 which is gel filled it also has a slightly tougher outer sheath too.
I concur with the connector assessment too Either use correct fitting solder or crimp (with the CORRECT tool) and butyl rubber waterproofing (3M 23 brand) covered with vinyl tape to keep the UV off.

[akopac]

Anybody have a tested Transmit/receive range on a B+ unit with a reasonable New antenna setup at mast top about 65 foot off water.
I have a Digital Yacht AIT2500/SPL2000 setup with vesper vhf/ais antenna. Pretty good coax, no splices top to bottom, and soldered connectors. Testing vswr this weekend. I’m just curious what to expect.

[Dockhead]

Originally Posted by PPLepew

.

My MAIN advantage is that I set a 15 min vector line on all vessels seen, including mine (40' sailing cat). And only have to see where they cross mine and give me an instant picture of my surroundings. No more guessing, it's all in front of me.

Where the vector lines cross is meaningless, unless they meet right at ends, and they are set for the same time.

[s/v Jedi]

- Marine VHF is 25W maximum, not 50W.

- One mast but two antennas? Put one on top of the upper spreader.

- Only SOTDMA transceivers do satellite AIS (msg 27). (Satellites will try to receive normal AIS as well but for low power CSTDMA transceivers this is very unreliable) See this excellent comparison guide: https://www.milltechmarine.com/custo...comparison.pdf

- For collision avoidance, check CPA and TCPA instead of watching vectors on chart plotters. Your software should sort it so that most dangerous encounters are listed first.

- For optimal working SOTDMA transceivers you need a special broadband antenna, not just an AIS antenna. The one from Vesper is good for bracket mounting just like the regular stainless whip antennas and the Shakespeare 6500-WB is good for mounting on standard 1” threaded antenna mounts (but requires the optional double-female ferrule for that) https://www.milltechmarine.com/shake...f-antenna.html
That 6500-WB is perfect for mounting on top of a spreader, but it is expensive.

- there are many old wives tales about why class-B transceivers aren’t seen by ships; most are around the myth that ships filter class-B out so as not to be bothered by yachties. They are all wrong, the real reason is that class-B can’t transmit in busy areas because of the flawed protocol.

- “good old class-B” no, there is nothing good about it. It is an abomination and we can only hope it goes away and everything is SOTDMA based.

[Dockhead]

Originally Posted by s/v Jedi

. . . - For optimal working SOTDMA transceivers you need a special broadband antenna, not just an AIS antenna. The one from Vesper is good for bracket mounting just like the regular stainless whip antennas and the Shakespeare 6500-WB is good for mounting on standard 1” threaded antenna mounts (but requires the optional double-female ferrule for that) https://www.milltechmarine.com/shake...f-antenna.html
That 6500-WB is perfect for mounting on top of a spreader, but it is expensive.. .

Thread drift, but can you explain this?



You may have just saved me from an expensive mistake, about to order (today!) two AIS antennae for two yachts.

[s/v Jedi]

Originally Posted by Dockhead

Thread drift, but can you explain this?

You may have just saved me from an expensive mistake, about to order (today!) two AIS antennae for two yachts.

Don’t order those! Let me get some details, I’ll post below in a bit

[s/v Jedi]

Okay, about antennas, channels and frequencies:

- a normal VHF antenna is tuned at 157MHz and has a 7MHz bandwidth so range 153.5-160.5MHz

- a regular AIS antenna is tuned at 162MHz and has a 7 MHz bandwidth so range 158.5-165.5MHz

- VHF channel 16 is at 156.8MHz so outside the range of a regular AIS antenna.

- AIS1 and AIS2 channels are centered around 162MHz so outside the range of a regular VHF antenna.

- SOTDMA AIS transceivers transmit message 27 packets on channels 75 and 76 which are centered around channel 16 @ 156.8MHz so outside the range of a regular AIS antenna!

- Vesper antenna is tuned at 159MHz with a 6MHz bandwidth so range 156-162MHz covering both VHF and AIS and thus SOTDMA AIS

- Shakespeare 6500-WB is tuned at 159MHz but covers a whopping 145-165MHz at 2:1 VSWR and even at 1.5:1 VSWR it still covers 156-162MHz, outperforming about everything else so very good for VHF, AIS and SOTDMA AIS.

[Dockhead]

Originally Posted by s/v Jedi

Don’t order those! Let me get some details, I’ll post below in a bit

Order cancelled

[sailjumanji]

Originally Posted by s/v Jedi

Okay, about antennas, channels and frequencies:



- a normal VHF antenna is tuned at 157MHz and has a 7MHz bandwidth so range 153.5-160.5MHz



- a regular AIS antenna is tuned at 162MHz and has a 7 MHz bandwidth so range 158.5-165.5MHz



- VHF channel 16 is at 156.8MHz so outside the range of a regular AIS antenna.



- AIS1 and AIS2 channels are centered around 162MHz so outside the range of a regular VHF antenna.



- SOTDMA AIS transceivers transmit message 27 packets on channels 75 and 76 which are centered around channel 16 @ 156.8MHz so outside the range of a regular AIS antenna!



- Vesper antenna is tuned at 159MHz with a 6MHz bandwidth so range 156-162MHz covering both VHF and AIS and thus SOTDMA AIS



- Shakespeare 6500-WB is tuned at 159MHz but covers a whopping 145-165MHz at 2:1 VSWR and even at 1.5:1 VSWR it still covers 156-162MHz, outperforming about everything else so very good for VHF, AIS and SOTDMA AIS.

Excellent info. Thank you. Just FYI, I've had good experience with the Vesper AIS/VHF combo antenna on last two boats. Using their SP-160 splitter with an XB8000. Antenna at top of mast.

[Dockhead]

Originally Posted by s/v Jedi

Okay, about antennas, channels and frequencies:

- a normal VHF antenna is tuned at 157MHz and has a 7MHz bandwidth so range 153.5-160.5MHz

- a regular AIS antenna is tuned at 162MHz and has a 7 MHz bandwidth so range 158.5-165.5MHz

- VHF channel 16 is at 156.8MHz so outside the range of a regular AIS antenna.

- AIS1 and AIS2 channels are centered around 162MHz so outside the range of a regular VHF antenna.

- SOTDMA AIS transceivers transmit message 27 packets on channels 75 and 76 which are centered around channel 16 @ 156.8MHz so outside the range of a regular AIS antenna!

- Vesper antenna is tuned at 159MHz with a 6MHz bandwidth so range 156-162MHz covering both VHF and AIS and thus SOTDMA AIS

- Shakespeare 6500-WB is tuned at 159MHz but covers a whopping 145-165MHz at 2:1 VSWR and even at 1.5:1 VSWR it still covers 156-162MHz, outperforming about everything else so very good for VHF, AIS and SOTDMA AIS.

That's really good to know; thanks.


But Message 27 is for satellites, right? And only active when well offshore? Do we really care if SWR is suboptimal for these messages? Surely we care a lot more about what we broadcast on the normal frequency, no?