Major disadvantage of Comar AIS Multi

[blackbeard]

I have a Comar ASR 100 splitter used with an ICOM radio and stand-alone NASA AIS receiver and display. Both radio and AIS work just fine, no problems (as with some other posts on this topic).
Comar recommend that the splitter has the same power circuit as the radio. They also say "In the event of a fault or power failure to the ASR 100 the VHF Radio transmit and receive will continue as normal".
The Comar "allows your existing VHF antenna to be used by both a VHF radiotelephone and an AIS receiver" which I take to indicate that it cannot be used with an AIS transmitter.

I suspect, therefore, that where a problem exists, either the hardware or installation are at fault.

It also seems clear that Comar, at least, do not expect damage to the radio from failure of their splitter.

I hope this helps. The vexed question of whether a separate aerial is a better solution remains. With hindsight I might have gone for a second aerial, largely because it could also be used as an emergency radio antenna, also could still be used should I upgrade to an AIS sender. There does not appear to be a clear cost advantage either way.

[demonboy]

Does this imply you've mounted both antennas in the top of the mast next to each other?

If so, I'm surprised the AIS receiver hasn't blown because of the power emitted from the VHF when sending.

I'm ketch rigged, so I have one on each mast.

Even so, I doubt the receiver would blow just because the VHF aerial was next to it. Many people only have one mast with the two aerials mounted next to each other, don't they?

[prv]

Even so, I doubt the receiver would blow just because the VHF aerial was next to it. Many people only have one mast with the two aerials mounted next to each other, don't they?

Not usually, I don't think. AIS aerials are often mounted on the pushpit, or occasionally on the spreaders. Two VHF antennas on the same masthead is probably not a very good idea.

Pete

[fireball]

Two VHF antennas on the same masthead is probably not a very good idea.

Unless you can get the correct amount of horizontal or - more practical - vertical separation...

[Sea_Spray]

Splitting / sharing antenna between devices has always seemed like an unnecessary complication to me. A good quality antenna, mounted on the pushpit it easy to fit, gives perfectly adequate reception, and offers the possibility of a fallback VHF antenna if your main fails (although most folk would probably just use a handheld...).

[moodyNick]

The AIS specs call for a dedicated antenna. All so called splitter solutions are NOT to be used. Why spend top $ on an AIS, save a few bucks on a separate antenna and compromise both AIS AND VHF.
If cost were the issue I'd rather use a dedicated coat hanger for the AIS than sharing an antenna.

its not the cost of the seperate antenna, it is the aggravation of having to mount it aloft and run the cable down a keel stepped mast and through the boat.

I have found a supplier of the Comar Multi unit, which includes the splitter, selling that a price less than an AIS engine alone. I will buy one and give myself the option of using the splitter initially - but then install a second antenna when I get around to it.

[maxi77]

I suspect that whilst this has flagged up as a Comar problem it is probably endemic with any splitter as there will always be losses that have to be compensated for by amplification. In the problem installations I suspect the answer is mismatched tolerances between different manufacturers, everything in spec but not working. Remember the old crystal VHF sets and the problems of finding a channel both you and your oppo could talk to each other.

The clear benefit of a second antenna is that you do now have a proper functioning spare

[robbieg]

I have run a Comar splitter with a Simrad VHF for over 3 years now and no problems at all that I can detect. I suspect Comar will have sold hundreds if not thousands of these units and if there were an endemic problem we would have heard about it by now.