AIS transponder AND integrated AIS receiver/VHF radio

[Auspicious]

Originally Posted by Cpt Pat

That configuration solves all the OP's issues!

I agree.

A moment to reflect on why VHF radios with built-in AIS receivers are "okay" while some of us are disenchanted with splitters is due. The AIS feed will be AFTER the radio T/R switch and first stage of amplification. This sets the noise figure for the signal chain and is unchanged from out-of-the-box performance of the voice VHF.

[slug]

Originally Posted by Pizzazz

There are many reasons to have separate antennas for VHF/DSC and AIS for large ships and they are mandated. The only issue that needs to be addressed is the receiver ignoring own vessel MMSI which most receiver only radios can do.

You can mount the transmitter antenna low - the reason for this is just being considerate to the other ships around you. A large ship will have its antenna mounted high, so you will get 10-15 nm range. A small power boat (antenna mounted low) will see you 5-10 nm out. There is no reason for a further detection range, especially if you are small (under 60 ft). You are just polluting the AIS display of the other boats.

Thus, you have little to gain with a high mounted transmit antenna. Use the receiver in the (high mounted) VHF radio antenna and the transmitter of the stand alone AIS system mounted low.

Finally, have a hand held VHF as back up.

AIS is a safety device .

Antenna installation must promote maximum transmission range , maximum visibility

[Auspicious]

Originally Posted by slug

AIS is a safety device .

Yes.

Originally Posted by slug

Antenna installation must promote maximum transmission range , maximum visibility

No.

[slug]

Silly statement

Visibility is the reason you spent 1500 dollars for the AIS

In addition it’s wise to choose a class b SOTDMA AIS to benefit from oceanic satellite ais tracking

https://cdn2.hubspot.net/hubfs/183611/Old%20Content/Landing_Page_Documents/Satellite_AIS_White_Paper_Final-1.pdf

[Sailmonkey]

Originally Posted by Pizzazz

There are many reasons to have separate antennas for VHF/DSC and AIS for large ships and they are mandated. The only issue that needs to be addressed is the receiver ignoring own vessel MMSI which most receiver only radios can do.

You can mount the transmitter antenna low - the reason for this is just being considerate to the other ships around you. A large ship will have its antenna mounted high, so you will get 10-15 nm range. A small power boat (antenna mounted low) will see you 5-10 nm out. There is no reason for a further detection range, especially if you are small (under 60 ft). You are just polluting the AIS display of the other boats.

Thus, you have little to gain with a high mounted transmit antenna. Use the receiver in the (high mounted) VHF radio antenna and the transmitter of the stand alone AIS system mounted low.

Finally, have a hand held VHF as back up.

I don’t buy this reasoning at all. I’m transmitting AIS to be visible.

If a large ship knows my position 20 miles out instead of 10, there is more time available for them to make a small course correction. Closer means less time and larger swings.

As for polluting, in the scenario where I want the range, there is less traffic anyway. Add to that sotdma and “polluting” makes even less sense.

[Pizzazz]

Everything is a trade-off. If you want max visibility, install class A AIS on a spreader. As it was pointed out previously, a handrail installation will give a large ship 17 nm detection (even higher because the waves bend a little bit). Which is plenty. A smaller ship will have less detection but they are also a lot more nimble.

The problem with two antennas on the mast top is difficult installation and wiring. The problem with splitters is signal loss.

Just to give you an example, The furthest away ships on my AIS display (50 ft masthead antenna) today are 31 and 32 nm. This is totally unnecessary. If I were transmitting now, all the ships in the shipping channel will be getting my signal and they do not need that. So, yes, it is pollution.

The other thing is that running coax to the top is not trivial. You need quality wire, ideally you want to put it into the mast channel (means mast has to come down), you will end up installing a few connectors (at mast base, to run through the boat, etc.). A perfect installation is not so straightforward and you will get losses.

It is typical that a 25W radio outputs only 7-8W on old wiring. If you really want your AIS signal to be visible by satellites, height does not matter but transmitted power does. In this case, rail mounting is best.

Not advocating one or the other - anyone can make a decision for herself but we need to have the basics straight, not just I want to be visible, so I want the biggest height.

[Dsanduril]

Up where we currently sail one of the primary advantages of AIS is "seeing" around blind corners. Elevation on both sides helps with that. The more elevation both parties have the sooner you will see over the promontory you are rounding. I'm far more likely to encounter a vessel in these situations than far out at sea, where overuse of the spectrum is unlikely.

As to splitter/no splitter, no splitter is technically superior for the transmitters. But that is not the whole picture. Two antennas means two antenna cables. Since antennas are generally outdoors and transmitters indoors that means twice as many deck penetrations to leak. Twice as many core penetrations to get wet and rot the core. Twice as many outdoor antenna connections to maintain. While it may reduce complexity in the transmitters it increases system complexity in other places. It's not binary.

[Auspicious]

Originally Posted by slug

Visibility is the reason you spent 1500 dollars for the AIS

In addition it’s wise to choose a class b SOTDMA AIS to benefit from oceanic satellite ais tracking

Your principal safety communication means is voice VHF. Don't do anything to degrade voice VHF. Putting a second antenna at the masthead WILL result in loss of omnidirectionality (unintended directivity). A splitter WILL result in reduced sensitivity on receive and reduced transmit power. A splitter WILL add additional failure modes that can damage mission-critical life-safety equipment.

I've addressed S-AIS before. It is not good for much beyond asset tracking and the data feeds are not readily available without expensive premiums. Class A generally show up a handful of times per day. Class B perhaps once per day. The big advantage of Class B+ for being heard by S-AIS is not SO over CS but higher power output. Atmospheric attenuation and spreading losses are not on our side. Also, SO is working based on VHF line-of-sight and the footprint of the S-AIS is huge so there are data collisions in time slots. It is all stochastic. Regardless, what good does it do to be heard by satellites when the vessels you care about are all using line-of-sight VHF receivers? Do care that a shipping company logistician sees a data point when s/he gets into the office in the morning that you were near one of their ships while that person was home in bed asleep? S-AIS is simply not relevant to collision avoidance.

About the best you can do for AIS is a separate antenna on a high spreader. If you can't or won't fish the cable for that, a radar pole or even the pushpit is adequate, assuming of course you are keeping a good watch.

[slug]

sattelite Ais is an SAR asset

You may ignore and retard your installation if you don’t value the SAR aspect of AIS

[Sailorman4009]

I have a vhf with ais receiver. My vhf antenna is at mast height. I installed an ais transceiver independent of the primary with its own combo antenna on the stern rail. That way if i get dismasted or lightning struck my ais is still there. Always install lightning arrestor in coax feed lines to your radios. Redundancy within simplicity is a good rule to stay safe out there.

[Auspicious]

Originally Posted by slug

sattelite Ais is an SAR asset

You may ignore and retard your installation if you don’t value the SAR aspect of AIS

EPIRB is a better SAR asset. It transmits your position from GPS over 406 MHz through satellites to GMDSS life-safety networks to MCC and RCCs who launch SAR. SAR assets use 121.5 MHz for direction finding to supplement GPS positions.

S-AIS is not timely and not consistent. I've never heard of anyone using S-AIS for SAR support. Footnote please?

Regardless, mounting your AIS transmit antenna high will not make a difference compared to on the pushpit. Talking about feet of difference in LOS to a satellite is specious in view of atmospheric attenuation and spreading losses for rising or descending satellites. The ones that will "hear" you are going to be at very high angles (well above the horizon).

See Atmospheric Absorption (Specific Attenuation) Chart - RF Cafe and https://en.wikipedia.org/wiki/Path_loss .

S-AIS is entirely intended for commercial asset tracking.

[slug]

Originally Posted by Auspicious

EPIRB is a better SAR asset. It transmits your position from GPS over 406 MHz through satellites to GMDSS life-safety networks to MCC and RCCs who launch SAR. SAR assets use 121.5 MHz for direction finding to supplement GPS positions.

S-AIS is not timely and not consistent. I've never heard of anyone using S-AIS for SAR support. Footnote please?

Regardless, mounting your AIS transmit antenna high will not make a difference compared to on the pushpit. Talking about feet of difference in LOS to a satellite is specious in view of atmospheric attenuation and spreading losses for rising or descending satellites. The ones that will "hear" you are going to be at very high angles (well above the horizon).

See Atmospheric Absorption (Specific Attenuation) Chart - RF Cafe and https://en.wikipedia.org/wiki/Path_loss .

S-AIS is entirely intended for commercial asset tracking.

http://cdn2.hubspot.net/hub/183611/file-281217356-pdf/Collateral_for_Download/SAR_Whitepaper.pdf?t=1377614119000

[Auspicious]

Originally Posted by slug

http://cdn2.hubspot.net/hub/183611/file-281217356-pdf/Collateral_for_Download/SAR_Whitepaper.pdf?t=1377614119000

exactEARTH is selling services.

S-AIS could very well become a fundamental pillar of the future GMDSS

S-AIS is not part of GMDSS. The only satellite service that is part of GMDSS is Inmarsat C. AIS-SART is part of GMDSS. VHF line of sight to the platform that lost crew and other vessels in line of sight, including synthetic AIS ATONs that have repeating capability.

Physics is not on the side of S-AIS with respect to SAR. They'll need much more sensitive receivers with lower noise floors and find a way to work around time slot collisions. For the later all I can think of are (expensive) multi-beam array antennas; someone may think of something simpler and more elegant. They aren't there and there is no sign of getting there. Remember that the people paying for S-AIS are interested in asset tracking and are not motivated to invest in SAR.

I like AIS-SART for terrestrial paths and PLBs and EPIRBS for satellite.

Are you associated with exactEARTH?

[CarlF]

Another reason to own a ketch

Two masts of different heights providing both vertical and horizontal separation for the two antennas.

[Auspicious]

Originally Posted by CarlF

Another reason to own a ketch

Two masts of different heights providing both vertical and horizontal separation for the two antennas.

Absolutely. Also a great place for a wind generator. Insulate a mizzen shroud and use in combination with the triatic and an inverted-L antenna will have a booming signal on HF/SSB. More spreaders to mount things on. Of course where the mizzen is stepped can make the aft cabin awkward. *grin*