AIS antenna performance

[Ric]

Currently my active AIS antenna - a Glomex stubby - resides below deck at the rear of the cockpit locker. Unfortunately, performance is not good and although it can pick up some targets 10 miles away, it often does not pick up targets that are straight ahead.

I'd like to move it up onto the transom but as I already have two GPS antennae and a Naztex antenna there is no room for another. The only reasonably feasible location would be to mount it on a stub-arm on the stainless tube that carries my Rutland 913 (obviously taking care to mount it below the blades doh!).

My question is would this work or would the proximity to the stainless pole completely mask reception and transmission?

Also, I wondered if I would get any worthwhile performance improvement if I were to get the AIS-dedicated Glomex stubby antenna? My only other option is to get a splitter and connect to the mast-head VHF antenna.

 

[Martin_J]

Hi.. I would question your inclination to a stubby antenna.

Are you able to mount a more normal 1.1m whip antenna on your pushpit?

Although before you try any changes, are you sure the connections are good to the stubby? Perhaps someone local to you could run an SWR/power test on your current stubby antenna and cabling.

Making use of the masthead antenna via a splitter will produce a better result (so long as you don't have too much of a lossy cable to the masthead).

 

[Georgio]

I won't comment on location but I was having problems with reception when using an "ais tuned" stubby antenna and when I contact the manufacturer of my AIS transponder we talked about the VSRW test errors being reported and the first question was about the antenna as they have experienced lots of problems with these stubby antennas due to poor earthling. I moved to a stainless steel whip antenna from Salty John and the problems were completely resolved.

Not sure if this helps but maybe swap over to a different/spare antenna and test.

 

[Pete7]

Ric, the two GPS aerials are passive so putting a AIS aerial next to them won't cause a problem. Whether you end up looking like a Russian trawler is another question.

Our AIS in on a 2m S/S pole on the stern out of the way. What do you have on the other side from the Rutland?

Just replaced the masthead VHF with a Saltly John whip and the more expensive RG8x cable, big improvement on the old VHF aerial.

Pete

 

[Heckler]

Currently my active AIS antenna - a Glomex stubby - resides below deck at the rear of the cockpit locker. Unfortunately, performance is not good and although it can pick up some targets 10 miles away, it often does not pick up targets that are straight ahead.

I'd like to move it up onto the transom but as I already have two GPS antennae and a Naztex antenna there is no room for another. The only reasonably feasible location would be to mount it on a stub-arm on the stainless tube that carries my Rutland 913 (obviously taking care to mount it below the blades doh!).

My question is would this work or would the proximity to the stainless pole completely mask reception and transmission?

Also, I wondered if I would get any worthwhile performance improvement if I were to get the AIS-dedicated Glomex stubby antenna? My only other option is to get a splitter and connect to the mast-head VHF antenna.

I have my cockpit dsc connected to a pushpit stalk antenna. The GPS is about a mtr below on the pushpit rail. On transmit the chartplotter reboots and the garden light led anchor light next to it goes out! So the moral, be carefull with antennas near each other!
As

 

[Daydream believer]

Any aerial for ais needs to be a dedicated ais aerial & i would suggest a whip version. It needs to be 1 metre from any other transmissions. I used a cut down sailboard boom fitted to the push pit. Having a neoprene cover on the lower part it is isolated from the pushpit. Having an extension section it can be raised 2 feet . Being originally for a sailboard it is strong
Most of its length is straight & i cut it where it started to curve so it directed the wire inside onto the deck gland
It is fitted to the pushpit with 2 u bolts.
I know your question is about aerials but this might help with the mounting

 

[Ric]

Ric, the two GPS aerials are passive so putting a AIS aerial next to them won't cause a problem.

Yes, the GPS antennae are passive - but I have active AIS so my AIS antenna is also transmitting. I'm concerned about degradation of the GPS signals if I have an active AIS alongside them.

Our AIS in on a 2m S/S pole on the stern out of the way. What do you have on the other side from the Rutland?

Pete

Yes, maybe another shorter pole might be a cheaper and easier solution than a stub on the Rutland pole.

 

[BrianH]

Currently my active AIS antenna - a Glomex stubby - resides below deck at the rear of the cockpit locker. Unfortunately, performance is not good and although it can pick up some targets 10 miles away, it often does not pick up targets that are straight ahead.
I'd like to move it up onto the transom but as I already have two GPS antennae and a Naztex antenna there is no room for another. The only reasonably feasible location would be to mount it on a stub-arm on the stainless tube that carries my Rutland 913 (obviously taking care to mount it below the blades doh!).
My question is would this work or would the proximity to the stainless pole completely mask reception and transmission?
Also, I wondered if I would get any worthwhile performance improvement if I were to get the AIS-dedicated Glomex stubby antenna? My only other option is to get a splitter and connect to the mast-head VHF antenna.

When I was installing my AIS transponder as a replacement to the 8-year old receiver-only this year I was tempted to buy a stubby version to replace the old receiver one on the wind generator pole. But then I bumped into the Italian Glomex manager in the marina who convinced me of the benefits of a 1/2 wave model (from his "30 years of installation experience" - "what is it you want, performance or convenience?").

So I installed the 1m Glomex on the pushpit on the same side as the wind generator. The results were poor and intermittent. As soon as I re-installed on the other quarter, still on the pushpit, away from the generator pole, the reception - both for me and the Marinetraffic receivers in Slovenia, 28nm away, improved dramatically.

Here is a typical screen snapshot of OpenCPN showing targets anchored off Trieste, 30nm distant to my berth in my Italian marina.

 

[Salty John]

Standard vhf antenna vs AIS optimised antenna: In most cases (but not all) the only difference between the two is that the whip on the AIS optimised version is around 1.5" shorter. This moves the tuning point from the centre of the vhf marine band range to the right hand side, about 162 MHz, and this gives a slight improvement in performance at 162 MHz.

This shifting of the tuning point is no problem on an antenna with a wide bandwidth but with some antennas it means the performance at the left hand side of the band diminishes significantly. If you are never going to use the AIS antenna for radio, by all means select the AIS optimised version; if you want to use the AIS antenna for radio at any time, pick the standard vhf antenna. If you have a combined radio/AIS, choose the standard vhf antenna, not the AIS optimised version.

A vhf antenna is "line of sight" so should be out in the open and mounted as high as is practicable. They don't like to be close to large vertical chunks of metal and should be at least 500mm from other antennae.


The forgoing refers to 1m whip antennas - "stubbies" are very compromised and I wouldn't recommend them.

 

[ianfr]

I have a "Salty John" Metz aerial on the pushpit, and in open sea, I get AIS targets up to 40 miles away.
Plugging in the masthead aerial gets targets as far away as Ostende. Being in the river Blackwater that makes it around 80 miles.
BTW the masthead aerial is also a Metz.

Ian

 

[Bobc]

When I recently fitted my AIS, I decided to use the masthead antenna for it, and fitted a whip on the transom for the VHF.

Worked splendidly, and as the VHF is on the transom, I don't need to worry about carrying an emergency antenna n case of being dis-masted.

 

[rob2]

If the stubby is below decks, it hasn't sufficient height for good performance and if your lockers are like mine there will be many items in them which would compromise performance, plus the engine block blanking off half its field of view. Others have already covered the AIS vs VHF tuning issues, which will be more important with a low gain, stubby antenna than with a whip aerial. I used to get reasonable VHF performance within the Solent with a stubby at the masthead and suspect that moving it to that height would sort your problems to an acceptable level. Incidentally, I don't think you really meant an active aerial, did you?

Another option to gain separation between aerials would be to mount it on the pushpit.

Rob.