Major disadvantage of Comar AIS Multi

[moodyNick]

Deliberately picking up on this old thread as I have been planning to buy one of these units.

I am wondering what happens to the VHF signal if the Comar unit fails or is depowered. Does it fallback to a direct connection?

Now I am also concerned about this S/N ratio issue.

Has anybody any further news?

[fireball]

Don't know about the multi - we have the normal dual channel comar engine on a dedicated antenna and very happy with it ... never been happy with splitters of any sort .. hopefully it's an unjustified prejudice!

[aluijten]

I am wondering what happens to the VHF signal if the Comar unit fails or is depowered. Does it fallback to a direct connection?

In this case, as soon as you start transmitting with your VHF you'll fry the receivers in the AIS receiver. After that it's anyone's guess what happens next. Ideally nothing and the VHF will still work, worst case the RF-amplifier is shorted out and is fried as well. You must make sure the power to the splitter is always present when the VHF is powered on.

It's a attractive solution to use a splitter in the effort to install but one that should be avoided if possible. As usual with these solutions it'll work under normal circumstances, but when the sh*t hits the fan these systems will always find a reason to fail.

[maxi77]

I have the same unit but with a dedicated aerial. I have found the Comar support excellent and a faulty unit was replaced without any quibble

[BlueChip]

I posted the original message with the problem. Since then Comar replaced the unit and I had the same problems with the new one. I had the VHF antenna and radio checked out and all are ok, so I never got to the bottom of the problem. I now use the Comar with a dedicated pushpit antenna and it works fine but that rather defeats the point of buying that particular model with the antenna sharing.

[moodyNick]

In this case, as soon as you start transmitting with your VHF you'll fry the receivers in the AIS receiver.

That depends on the design of the unit, which is what I am trying to find out.

I have always been concerned about separate splitters and avoided them. Now I am trying to avoid the hassle of a second antenna installation, so want to find out more.

[moodyNick]

I posted the original message with the problem. Since then Comar replaced the unit and I had the same problems with the new one. I had the VHF antenna and radio checked out and all are ok, so I never got to the bottom of the problem. I now use the Comar with a dedicated pushpit antenna and it works fine but that rather defeats the point of buying that particular model with the antenna sharing.

Thanks BlueChip, that's a great help !!

[jfkal]

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.

[demonboy]

I have a COMAR too and it saw us safely from Turkey to India.

The one piece of advice I was told when researching this subject was NEVER SPLIT THE VHF AERIAL, no matter what gizmos you are told will do the job.

With this in mind I ran two independent aerials for each AIS and VHF down my rigging and through the deck. I used self-amalgamating tape around the cables to the rigging and whilst it wasn't the prettiest solution I have never had a problem (actually, you barely notice it). Since we were about to embark on a long journey through busy waters it was a case of opting for a practical solution, and this was it.

Whilst you already know that separate aerials is ideal but not practical my advice is run separate aerials no matter how difficult or ugly they are to install.

Sorry if this isn't solid technical advice, it's just my personal experience.

[aluijten]

With this in mind I ran two independent aerials for each AIS and VHF down my rigging and through the deck.

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.