AIS / VHF / RTE - Frying tonight?

[Tintin]

I'm about to install an ais transponder and an echomax dual band thingy (tax refund came in handy, hurrah).

I've got two VHF aerials at the masthead currently. One is for the VHF. The other (old fibreglass pole type) is currently used for the AM/FM radio. Both have plugs in the same place so if the AM/FM aerial dies I can dump the VHF and still listen to the Archers (only kidding - you know what I mean I hope - as a spare VHF aerial).

The ais came with a "tuned" stubby.

I can't really be ars3d running another coax up to the masthead, so the question is which aerial to use for what?

My first thought was to fit and use the stubby on the pushpit for the AM/FM Archers reception, replacing the old masthead fibreglass thing with a Metz, maybe also replacing the other with a 2nd Metz, then using one for the VHF and one for the AIS Transponder. With all plugs coming back to the same place so I can have plenty of emergency options.

What I am cincerned about with this is that the distance between the to masthead aerials is no more than 25cm, so am I likely to fry either the ais when I transmit on VHF, or the VHF when the AIS transmits.

And just for an added bit of fun an active dual band echomax is also going up there, or may just go on the pushpit, because again running the cable is one royal pain.

So, thoughts and wisdom from the assembled masses pls......

 

[pappaecho]

I have the same setup. The radio fm/am seems to mix well with the AIS system, as they are receive only.
The marine VHF puts out 25 watts which would not do the Archers and the AIS any good...if on the same aerial

 

[Tintin]

I have the same setup. The radio fm/am seems to mix well with the AIS system, as they are receive only.
The marine VHF puts out 25 watts which would not do the Archers and the AIS any good...if on the same aerial

Thx. Just to clarify, the ais is tx/rx, not just rx. I am not thinking of any of them sharing an aerial.

 

[Doug_Stormforce]

If you want to share an antenna you can buy a splitter that stops the VHF signal going into the AIS and vice versa, the splitter is easy to Install and saves having an extra antenna.

 

[whipper_snapper]

If you want to share an antenna you can buy a splitter that stops the VHF signal going into the AIS and vice versa, the splitter is easy to Install and saves having an extra antenna.

Seems a bit pointless to contribute if you have not read either post from the originator of the thread.


FWIW, I would leave the existing system exactly as it is and mount the AIS aerial on your pushpit. Not only does it avoid the problem of having two aerials transmitting virtually the same frequencies so close to each other, it also provides a backup for the VHF in the event of dismasting.

 

[st599]

The antenna patterns will no longer be omnidirectional.

There's a chance, if the front end overloads, of damaging the input of radio or ais.

 

[Bosun Higgs]

So, thoughts and wisdom from the assembled masses pls......

The general advice is that VHF aerials ( and that includes AIS ) should be at least 1 metre apart. I would put the AIS aerial down at deck level - do you really want to know the course and full details of a ship 20 miles away or are you really interested in 3/4/5 miles when you might need to take action? I dont see the ultimate range as important on AIS.

Arent Metz the aerials with a PL259 plug at the aerial end? If so, I would avoid - that plug is not designed to be waterproof. And water into the coax is a common cause of aerial failure.

 

[Twister_Ken]

My AIS (RX only) has its aerial on the pushpit rail. In good viz, I generally see the ship a few minutes before the AIS does, so range is a bit less than the horizon. That's plenty for me, but YMMV.

 

[whipper_snapper]

Arent Metz the aerials with a PL259 plug at the aerial end? If so, I would avoid - that plug is not designed to be waterproof. And water into the coax is a common cause of aerial failure.

Yes they are, but in practice they seem to perform well with the connection swathed in self amalgamating tape. I have had one at the masthead for 3 years and it is still performing faultlessly. I doubt that the horrible push-fits or pre-installed connections on other types are actually any better.

 

[Jabs]

Echomax

You might want to think about the position of the Echomax. I was originally going to put mine on the masthead. If you think about it, at that height it will pick up merchant ships from miles and miles away.

I elected to fit mine on the pushpit to deliberately reduce the range.

If you read the Echomax site, it tends to support this view.

The danger of having it up high is that you will get so many alerts, it will end up turned off.

Tony.

 

[Salty John]

Arent Metz the aerials with a PL259 plug at the aerial end? If so, I would avoid - that plug is not designed to be waterproof. And water into the coax is a common cause of aerial failure.

Yes, the Metz has a PL259 connector at the base as do all high quality VHF whip antennas. The top of the range Shakespeare antennas also use this connector system. Some larger commercial antennas use a factory fitted RG213 coax tail with an N connector.

Factory crimped systems for pleasure boats usually implies connection to RG58 cable which is unsuitable for long runs and they don't facilitate removal of the antenna when the mast is down, without stripping out all the cable.

Metz has been making the Manta VHF antenna this way since 1977. The SO239/PL259 coupling is mechanically strong, the PL259 is reliably attached to the cable and can be easily checked before installation.

All external connections should be protected with self amalgamating tape, preferably silicone non-adhesive compression tape which leaves no sticky residue when removed.

 

[forelle541]

Can you not set the range on the AIS receiver so as only to pick up local ships with a mast head aerial?

 

[Tradewinds]

Metz is far superior to the Vitronix cr*p.

Just follow what Salty John says re the amalgamating tape.

 

[Jabs]

Can you not set the range on the AIS receiver so as only to pick up local ships with a mast head aerial?

You can set the alarm range on the plotter.

Why??

Don't understand the issue??

Tony.

 

[whipper_snapper]

Metz is far superior to the Vitronix cr*p.

Just follow what Salty John says re the amalgamating tape.

Lakesailored?

 

[prv]

Can you not set the range on the AIS receiver so as only to pick up local ships with a mast head aerial?

You can set the alarm range on the plotter.

Why??

Don't understand the issue??

I think he's misread your previous post and got confused between the AIS antenna and the radar target enhancer.

Pete

 

[Jabs]

I think he's misread your previous post and got confused between the AIS antenna and the radar target enhancer.

Pete

OK, yes, I see now.

Tony.

BTW, Metz is the most superb piece of kit on the marine market!

I won't have anything else!

 

[Twister_Ken]

You might want to think about the position of the Echomax. I was originally going to put mine on the masthead. If you think about it, at that height it will pick up merchant ships from miles and miles away.

I elected to fit mine on the pushpit to deliberately reduce the range.

If you read the Echomax site, it tends to support this view.

The danger of having it up high is that you will get so many alerts, it will end up turned off.

Tony.

The point of the Echomax RTE is not to generate alerts (although it does) but to make you visible to radar. Can't see why you wouldn't want that to be at the greatest possible range.

 

[Billjratt]

The "old fiberglass pole", if it's undamaged, will be a higher gain than the others, but will suffer from having a flatter radiation pattern which may be a disadvantage if the boat is heeled. If I had one already fitted I would leave it alone.
How about mounting the AIS antenna on a spreader if there's adequate room?

 

[Jabs]

The point of the Echomax RTE is not to generate alerts (although it does) but to make you visible to radar. Can't see why you wouldn't want that to be at the greatest possible range.

Because if I'm sleeping, I don't want to be woken by an alert from a ship thirty miles away.

I want max range on my AIS receiver where I can adjust the alarm setting but not on the Echomax where I can't!

I will rely on the Echomax also to pick up small craft with radar but without AIS and, again, don't want to know until they are maybe four miles away.

But I welcome the debate.

Tony.