Do I need to have two antenna?

M

mikecontessa26

Well-Known Member
Joined
23 Jul 2008
Messages
248
Visit site
Hi, I'm doing a complete refit (and i'm feeling tired) do i need two antenna for running VHF, FM and AIS receiver?

Can anyone recommend a splitter? I can see the benefits of having two antenna in case of failure of one etc. but mast space is at a premium. If I did go for two do they have to be a certain distance apart?

Also, what antenna do i need? I have a Cobra DSC VHF?

Thanks as always, i'dbe lost without this forum.

Mike /forums/images/graemlins/confused.gif
 
You could use an Easysplit or Comar splitter and the VHF antenna. There is not a perfect overlap between the AIS and VHF frequencies but in our experience the AIS unit will work very well with a VHF antenna. We use a splitter on our own yacht with an AIS transceiver and it seems to work well.
 
Hi Mike,

You'll find split (excuse the pun) views on here about this one (discussed many times before). I've used an Easysplit before and run a NASA AIS engine and the VHF through the mast head aerial. It worked but some folk who probably know more about these things than I do were concerned that if the splitter went wrong then you could fraz your AIS when transmitting on the VHF. There's a 'redundancy' argument for going with completely seperate systems. I think the aerials should be 1 metre apart, which on a mast head means vertical seperation of the two aerials. I'm about to go down this route again on a new (to me) boat, and I'm tempted to leave the VHF alone with mast head aerial... and (queue the doubters) use a stub aerial on the pushpit for the AIS... I know about line of site reception etc... but most of the things you're interested in on AIS have their aerials some way off the waterline and so as long as I get 10 -12 miles range I'm happy!! This would also leave a back up aerial that I could plug into the VHF if dismasted etc.
 
I'm not up on splitters - Gavin should be able to assist re the failsafe of a splitter ...

However, on our boat we have 3 antennas ....

1 at the masthead for VHF
1 on the pushpit for AIS (gives a range of around 15Nm give or take)
1 cheapo HalFds car ariel in the tall locker for FM
 
Well - I've got a Rib Raider on the pushpit - this is the thin stick with a curl in the middle - I've not found that I get my eye anywhere near it, but you could always put a cork/foam ball on the end of it (we use these for Radio Controllers for the RC Laser - works fine, even with 20 ppl walking up and down the path next to the course)
 
[image]
safetyglassessign.jpg
[/image] /forums/images/graemlins/grin.gif
 
Exactly what works for me too. The AIS & VHF are sited very close to each other. I can easily swap the antennas over if required. i.e. worst case if the mast comes down.

IMO I would not put anything between the VHF & its antenna other than a piece of coax & a plug. When you're really in the poo & it needs to work is the time you find the splitter has a fault.

Even a really expensive pushpit mounted antenna will cost far less than a splitter & you get redundacy. The loss of range really isn't an issue. Do you really need to know where an AIS target is at 15miles range? Anything out that far just complicates matters. In a really crowded area, you work on the closest targets and avoid them as they come up. If it's not crowded, then at 15nm, you have plenty of time to react anyway.
 
AIS uses chan 87 & 88 of the marine VHF spectrum, so will be costly to protect it from the ship's VHF transmissions on a shared aerial.
I share on RECEIVE only - TV, Domestic (car type)radio and anything else, separated (split) by capacitors (cost pennies or less if you scrap equipment properly).
I believe transmitters on boats, whether VHF HF LF etc. should have dedicated aerials as they could be construed as safety equipment.
 
I agree with the concept of dedicated antennas for VHF and AIS, the latter at deck level to provide a back up for the radio in the event of a dismasting. Put a PL259 connector on the end of the AIS cable so that it will plug into the radio and then use a BNC SO239 adaptor to connect to the AIS.
 
[ QUOTE ]
AIS uses chan 87 & 88 of the marine VHF spectrum

[/ QUOTE ]

AIS actually uses the shore-ship frequencies of Ch 87&88 (161.975 and 161.025), leaving the ship-shore frequencies free for simplex working (I have found a couple of sets which were set up this way). The highest frequencies you are likely to transmit on are M2 (161.425), and M (aka 37, 37A, or M1) (157.85).

I agree with the recomendation for separate antenna, - I have ended up with 3 - masthead, AIS mounted on the backstay and emergency on the pushpit.

John
 
[ QUOTE ]
What about the FM arial, could this be used on the AIS arial?

[/ QUOTE ]

When I first fitted AIS it was receive only (NASA Engine), and I fed this from the emergency VHF on the pushput via an FM/VHF splitter. This worked fine for the AIS engine and FM, but would not pick up LF (198). The splitter is mounted unter the cabin VHF set, and also provides a convenient point to park the plug from the emergency VHF.

The back-stay mounted antenna is a dedicated AIS one, and used to transmit as well.

John
 
We have an easysplit servicing VHF, AIS and FM radio. Works great, highly recommend. Have a handheld vhf, should the worst happen.
 
[ QUOTE ]
Have a handheld vhf, should the worst happen.

[/ QUOTE ]At 5w that ain't transmitting very far .... ok for coastal hopping, but no good once you're out of sight of land ....
 
With an EPIRB and Satphone, reduced range because of a dismasting I'm ok with but appriecate it could be better. Will probably get an emergency antenna.
 
Australian Yacht Racing rules require that where a radio is required and the antenna is on the mast a second antenna must be available for use in a dismasting. This is just good sense. So if you must have an antenna on the pushpit as a standby VHF com antenna then why not use this as AIS receiver antenna. Just have the connectors compatable for an exchange. olewill
 
On the subject of connectors, my emergency antenna is wired via a socket in the cockpit, and I have connectors and a cable ready made to enable me not only to connect the main VHF to either antenna, but also to connect my handheld to either antenna, from the cockpit or the saloon.

This way, even if the main radio fails, I can still push out 5W from the masthead.
 
You must log in or register to reply here.

Share this page

Top