AIS Transceiver in VHF

[s/v Jedi]

Originally Posted by DotDun

I don't understand how a separate AIS antenna and coax adds more failure points to VHF comms (which was my earlier point).

The probability of malfunction or failure occurring is twice as big if you have two antennas compared to only having one. Same goes for the coax cable: when you have two, the chances of a problem double. The reason a cable is worse than the antenna is because the cable (and attached connectors) is much more prone to failures.

So if you compare an automatic switch with an extra cable+antenna, then logic dictates that the switch is only one additional component so more reliable. However, the switch requires a small coax patch cable and, being an active component, may be more prone to failure than an antenna. From what I have seen it is about as reliable as a coach cable with connectors. If people buy a coax patch cable, I see little problems with that.

In short: the automatic switch is just as reliable as an extra coax cable and antenna. This is not (should not be) a factor for making the decision.

Why did the designers make Class B 2 watt? Maybe to limit the distance???

No they did not. For VHF radio communications, the distance is based on line of sight, i.e. antenna elevation, not on power. You can communicate with the Space Station using milliwatts and even bounce a signal from the moon back to earth.

No need to calculate, I have real-world experience.
Rail-mount to rail-mount Class B is 4nm to 8nm.

I'm sorry but that is nonsense. The real world is bound by the scientific laws; anything outside that is a trick or illusion. Your lower limit of 4nm is what I wrote and conforms to science. The 8nm is an illusion; probably when both sides sit on the top of a wave at the same time which can easily double range or even more. When both boats of my example are lifted by an 8 foot wave, their range becomes 8nm.

The thing is that you must (-must-) work with the math for reliable communications because this is a safety system (what I always call a "primary" system, like bilge pump, rudder etc.) When HAM radio operators make long distance links it is for fun and the stranger the fluke, the more fun it is. For boat/ship AIS communication range you must work with rock solid, reliable range, not a fluke or best-case scenario.

What do you do navigation-wise when you see a Class B vessel at 10nm? The answer is nothing! Hence, my point, for navigation you don't need to see Class B at 10nm nor Class A at 20-50nm.

I do nothing with any target regardless of range until the time that my system generates an alarm. A target at 1nm sailing away from me is of less importance than a 10nm range target that is heading towards me.

People should not try to interpret raw data, this is what causes incidents. Any good AIS plotter can reliably generate alarms. My black box Vesper XB-8000 with the new SmartAIS software loaded can even generate alarms without being on a plotter screen at all! This allows the crew to perform other tasks, even if that's just keeping visual watch or situational awareness: both tasks that enormously improve safety

It's easy to deal with except during an emergency when you really need the VHF comms...

I would like to know the scenario that you think of while writing that. For any kind of emergency, you always have the big red satellite button to press?

My real point is more for the newbies reading this thread thinking they need to see approaching vessels at 10, 20, 50nm away in order to avoid a collision. That's pure BS!!!

Agreed. You don't need AIS at all to avoid collisions. I sailed 35 years without and never a collision

It's like the guy I was talking to and he was complaining the PO of his boat installed a depth sounder that only read to 200'. He said he doesn't fish, I asked him the draft of the boat.....he didn't get it.

He could have said that he also uses it as a navigation tool. I know I do but mine doesn't even read to 200' I think :-)

[DotDun]

Originally Posted by s/v Jedi

The probability of malfunction or failure occurring is twice as big if you have two antennas compared to only having one. Same goes for the coax cable: when you have two, the chances of a problem double. The reason a cable is worse than the antenna is because the cable (and attached connectors) is much more prone to failures.

So if you compare an automatic switch with an extra cable+antenna, then logic dictates that the switch is only one additional component so more reliable. However, the switch requires a small coax patch cable and, being an active component, may be more prone to failure than an antenna. From what I have seen it is about as reliable as a coach cable with connectors. If people buy a coax patch cable, I see little problems with that.

In short: the automatic switch is just as reliable as an extra coax cable and antenna. This is not (should not be) a factor for making the decision.

You are missing my point. I stated adding a splitter to VHF comms adds a failure point to VHF comms. Adding a separate coax and antenna for AIS does not add a failure point to VHF comms.

VHF radio - coax - antenna

vs.

VHF radio - coax - splitter - coax - antenna

[DotDun]

Originally Posted by s/v Jedi

No they did not. For VHF radio communications, the distance is based on line of sight, i.e. antenna elevation, not on power. You can communicate with the Space Station using milliwatts and even bounce a signal from the moon back to earth.

Hmm, so power has nothing to do with distance.

Why are the comms radios 25watts????

[s/v Jedi]

Originally Posted by DotDun

You are missing my point. I stated adding a splitter to VHF comms adds a failure point to VHF comms. Adding a separate coax and antenna for AIS does not add a failure point to VHF comms.

VHF radio - coax - antenna

vs.

VHF radio - coax - splitter - coax - antenna

You are missing my point: you are leaving out the AIS transponder. Nobody puts an automatic antenna switch on their VHF radio without AIS. Following your logic, adding a VHF to a boat adds a failure point as well, because having it is voluntary as much as AIS is for boats under 20 meters LOA.

The AIS is more important than the VHF. You can always grab a handheld radio but they don't have an AIS transponder yet.

[s/v Jedi]

Originally Posted by s/v Jedi

You are missing my point: you are leaving out the AIS transponder. Nobody puts an automatic antenna switch on their VHF radio without AIS. Following your logic, adding a VHF to a boat adds a failure point as well, because having it is voluntary as much as AIS is for boats under 20 meters LOA.

The AIS is more important than the VHF. You can always grab a handheld radio but they don't have an AIS transponder yet.

I know I'm quoting myself but editing risks other posts before I finish :-)

It is only when you go without AIS transponder that your system becomes more reliable. The reason is that you have less gear so less can go wrong. When you have completely separate systems for VHF and AIS then the reliability is not better than for a system that shares the same antenna and cable for VHF and AIS.

[DotDun]

Originally Posted by s/v Jedi

You are missing my point: you are leaving out the AIS transponder. Nobody puts an automatic antenna switch on their VHF radio without AIS. Following your logic, adding a VHF to a boat adds a failure point as well, because having it is voluntary as much as AIS is for boats under 20 meters LOA.

The AIS is more important than the VHF. You can always grab a handheld radio but they don't have an AIS transponder yet.

I disagree with this! But, you do what you want on your boat!

[DotDun]

Originally Posted by s/v Jedi

I know I'm quoting myself but editing risks other posts before I finish :-)

It is only when you go without AIS transponder that your system becomes more reliable. The reason is that you have less gear so less can go wrong. When you have completely separate systems for VHF and AIS then the reliability is not better than for a system that shares the same antenna and cable for VHF and AIS.

You went to a different statistics class than I did.....when 2 is not better than 1.

[s/v Jedi]

Originally Posted by DotDun

You went to a different statistics class than I did.....when 2 is not better than 1.

Please don't do that. The math of probability of failure assessment is not a matter of opinion but fact.

When you have 2 coax cables, the chance of a failure is twice as big as for having one.

You confuse this with having a spare. In that case, you need two radios, two AIS'es, four coax cables and four antennas.

Or, your view (and I believe this is the case) is that AIS is "expendable", i.e. no problem if it fails as long as you keep VHF radio. I can understand that in case you have no other VHF radio. I have 4 other radios and almost every boat I meet has a minimum of 2 extra. I never met anyone without at least a handheld.

[DotDun]

Originally Posted by s/v Jedi

Please don't do that. The math of probability of failure assessment is not a matter of opinion but fact.

When you have 2 coax cables, the chance of a failure is twice as big as for having one.

You confuse this with having a spare. In that case, you need two radios, two AIS'es, four coax cables and four antennas.

Or, your view (and I believe this is the case) is that AIS is "expendable", i.e. no problem if it fails as long as you keep VHF radio. I can understand that in case you have no other VHF radio. I have 4 other radios and almost every boat I meet has a minimum of 2 extra. I never met anyone without at least a handheld.

Do you climb the mast to use the handhelds???? After all, deck mount antenna is not very useful (unless you are talking to the space station)!!!

Yes, my AIS is expendable. And my VHF comms system has less failure modes than yours.

Like I said, you can put anything you want on your boat, I don't care. Just don't tell newbies they must see AIS Class B targets at 10nm or they'll get run over.

[deluxe68]

Originally Posted by DotDun

Hmm, so power has nothing to do with distance.

Why are the comms radios 25watts????

Not when it comes to VHF.

[deluxe68]

People are talking about VHF/AIS antennas on the rail. Isn't there a radiation issue here? My B&G installer would not put an antenna on the rail unless I added a bimini arch to get the antenna up around 6 feet off the deck.

[barnakiel]

In this case 2 antennas are a better deal:

- they have the same connector so if one antenna fails, you still have at least one device (VHF or AIS) and you can swap by unplugging / plugging the antennas.

Failure statistics is pragmatically irrelevant here as I do not believe antennas fail more than 1 in 100. This makes 0.99x0.99/reverse ratio failure risk. This happens to be about the same for a single antenna and splitter - if we assume splitters fail at 1 to 100. But my gut feeling they fail more than that. So, in effect, two antennas may still be the 'more fail-proof' solution. Maybe. Maybe not.

Let alone the fact that splittet/antenna is only set for one fqcy while two antennas can be tuned to two slightly different fqcies. This may improve AIS reception/range.

The donkey is dead now. It is all in our perceptions way more than in the statistics.

Or, if any of you is still serious, pls link to statistics of vhf antennas failures and vhf splitters failures. Then we can run the calculations and find out "who is right".

b.

[sailjumanji]

Originally Posted by deluxe68

People are talking about VHF/AIS antennas on the rail. Isn't there a radiation issue here? My B&G installer would not put an antenna on the rail unless I added a bimini arch to get the antenna up around 6 feet off the deck.

I think that is true for radar, but have never heard that for vhf, ais or GPS.

[moniia]

Originally Posted by s/v Jedi

The probability of malfunction or failure occurring is twice as big if you have two antennas compared to only having one. Same goes for the coax cable: when you have two, the chances of a problem double. The reason a cable is worse than the antenna is because the cable (and attached connectors) is much more prone to failures.

(...)

)

I have to disagree. Of course, statistically speaking you're right. But there is a practical dimension to that.
My Vesper (same like yours, so as you know, black box, OK, painted blue...) sits next to the radio. On which I have AIS receiver as well. If anything happens to one of the antennas I still have a second set, also high on the mast (one sits on the top, the other one a bit lower on the upper spreader). Which means that in case of failure of one, I can connect WHAT I NEED MOST AT THE TIME to the working antenna set. Will it be AIS transponder, or radio VHF with AIS receiver depends on circumstances at this particular time. And I'll definitely have time to dig in the locker and get an emergency VHF antenna which on my boat gets hoisted on a backstay (in case mast is still standing) fair bit up. So after about half an hour I'll have again two antennas up and running.

[jeffrobbins]

Originally Posted by sailjumanji

I think that is true for radar, but have never heard that for vhf, ais or GPS.

GPS is a receiver so it doesn't apply to it. However, it does to VHF. Look for the MPE (max permissible exposure) in the manual for the radio or AIS. It is determined based on the transmission frequency, power output, expected antenna and duty cycle. For Vesper Marine AIS units it is 1m radius. For a 25W VHF the answer will be different.