AIS

Hello out there,
Does anyone have experience with fitting the AIS. A simple question: can we use the existing VHF antenna with a splitter to get AIS data or is this alternative so bad that we need to install a dedicated AIS natenna?

Cheers/Philippe
Swan47

Hi,
you are raising a difficult question amply discussed among boaters (see for example the newsgroup rec.boats.electronics). There are pluses and minuses in both solutions.
The accident that may happen in an antenna splitter is that something goes wrong in the electronics and while transmitting with the VHF, 25W are fed to the AIS receiver destroying it.
I still do not own an AIS receiver but it is high in my list and I already have the system to display its output. In fact I am still undecided whether to buy a true (parallel) two channel receiver or a switching unit. Regarding the antenna I have almost decided to put a new one low aft for the AIS and let the VHF use the topmast by itself. Most of the experts agree that the AIS receiver does not need a very large horizon so that a high antenna is not really needed.
I am quite interested in knowing your decision and, possibly, the receiver you have or will buy.

Regards
Daniel

Hello Daniel,

Thank you for a nice and well informed answer. While posting my question, I have discussed the issue elsewhere and the verdict is very much the same as your conclusion. The AIS antenna should be a dedicated one with aspecific span of about 161, 975 and 162, 025 Mhz. The VHF antenna is far too wide and, in addition to that, there is the problem related to the splitter sharing the occasional high voltage, as you rightfully explained. My conclusion:

I'll go for a dedicatd antenna. Perhaps fitted aft or perhaps on the masttop. I will try it aft first and see. If it is as you say, that the AIS data flowing through the antenna does not need to be fitted high on the top of the mast, then I will be happy to avoid the extra work. The AIS engine I have ordered is the Two Channel AIS Receiver "EASY AIS. It cost ? 250 and it seems to be an excellent piece of quipment, far ahead of the cheap NASA. look at this link for details: http://www.yachtbits.com/ais/ 

My displaying possibilities of the AIS data will be taken care of by Maxsea (an excellent software by the way) on the laptop and its repeater in the cockpit.

Cheers and fair winds

Philippe//S/Y Farouche Swan 47  

Hi, thank you for the information. The receiver you have chosen appears to be very good indeed (possibly the best for its price) but I am not sure if it is a truly two parallel channel listener. Maybe the two channels are fast duplexed so that they are practically monitored in parallel but I am not sure. Anyway, I believe that this is a very good choice and it will be soon in my shopping list too...

Regards
Daniel

Hello out there,
Does anyone have experience with fitting the AIS. A simple question: can we use the existing VHF antenna with a splitter to get AIS data or is this alternative so bad that we need to install a dedicated AIS natenna?

hello Philippe,
though we haven't experience yet with AIS we can say this as we have studied the options. (and a lot of experience in electronics) the VHF antenna is compatibile with the receiver AIS, but the problem is the VHF transmitter in transmition will damage the AIS receiver. therefore the split is an obligated option if you wish to use the same antenna. if you wish to install another dedicated antenna for AIS it still needs to be far enough away so as not to create the same damage as if it were the same antenna (at least 1mt. but best more than that). this problem on big ships has obviously not been an issue, but on a 47 we have a lot less space, and we are already full of antennas. please let us know what you decide and how it works out if possible.
thanks.
jayne and francesco
aorangi 47/047

Philippe, I have a Trueheading AIS receiver and transmitter installed on a stern mounted radar dome pole. We tested it in a storm in the Baltic last summer and It is incredible. As it was explained to me, you can put a splitter on an AIS receiver but not on a transmitter. You can't put the AIS antenna near your VHF antenna and the tops of masts are not installation platforms with extensive space. I was also concerned about having that maximum range. In fact, the installation we did, under 4m above the waterline turned out to pick up ships way over of the calculated range (about 15M). I felt much safer with the AIS than with radar, though one must not forget that there are a lot potentially dangerous boats that are not required to carry AIS. a presto Pippo