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Old 06-10-2014, 17:57   #1
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AIS and RF interference

Dear all, and specially radio communication specialists,

I am just about to install a new AIS receiver/transmitter to my existing nav station. I read the instruction manual and there is the usual safety notice that the unit will of course be almost lethal if not used properly, but my attention got caught by the RF notice... I understand that , like most antennas, one should allow for the required free space around it and etc...

But... should I also worry about RF interference with my HF(SSB) radio set-up (Icom 706, mk2). I use it along with Pactor modem to receive weather and exchange on daily networks when offshore. My current set-up works fine, and I have heard lots of horror stories with regards to interference vs. HF radios... All of this nice equipment would be neighbours in the space behind the nav station panel.

Could any of you share some words of knowledge on the subject?
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Old 06-10-2014, 20:13   #2
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Re: AIS and RF interference

If you are worried about it, power the AIS down while the SSB is in use.
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Old 07-10-2014, 00:28   #3
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Re: AIS and RF interference

It is very unlikely that your AIS transponder will interfere with your SSB radio. The frequencies are vastly different, and the AIS power level is reasonably low (equivalent to a VHF radio, or less). I have a transponder with the antenna close to the backstay SSB antenna and have had no problems.

It's possible that the NMEA data that your transponder sends to your chartplotter / computer might interfere with the SSB, but the same can be said for your GPS or other NMEA sources. Proper wiring practices should be sufficient.
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Old 07-10-2014, 02:01   #4
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Re: AIS and RF interference

Our Watchmate does get into the HF, also, and we do as suggested above, turn it off for radio scheds.

Ann
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Old 07-10-2014, 02:44   #5
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Re: AIS and RF interference

With AIS becoming popular the opportunities for interference are there. I would also worry some about AIS to VHF interference. For that just make sure the AIS VHF antenna is more than a meter from the VHF comm antenna. Or use a good quality splitter as there are some splitters with poor performance.

We can't just turn off everything when HF is needed. I like to get weather data from WeFAX and that can take a few hours. To minimize interference make sure you have enough Ferrites for all data cables. Put the AIS VHF antenna at least 1 meter away from the SSB antenna. Run the VHF coax as far from the SSB tuner output wire and coax as possible. Then test the systems for interference. Interference can go both ways so test everything with all systems operating. Be alert for other inboard interference sources such as LED lighting, inverters, battery chargers (some solar units are really good interference generators) and anything else with a switching supply. These devices can interfere with SSB as well as VHF reception.

There are some good SSB stickies here on CF.
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Old 07-10-2014, 05:17   #6
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Re: AIS and RF interference

I dont have HF. My AIS does not affect any other kit or visa versa in the Nav station.

BUT

I have a LED masthead nav light, Bi Colour, not tricolour, and when that is on it cuts down my AIS receive range from 20 to 25 nms to 10 to 15nms, so quite considerable! The Raymarine service agent recommended a ferrite which I put up the top of the mast but didnt do any good.

So I use the deck level nav lights only
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Old 07-10-2014, 07:41   #7
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Re: AIS and RF interference

More info on my question:

The AIS unit I purchased (Garmin AIS 600) can "share" the existing VHF antenna, no extra antenna, no splitter needed. They claim I can just connect the existing antenna coax to the AIS, then interconnect the AIS to the VHF. Looks like the splitter is built-in.

Anyway, I'm gonna wire it exactly like recommended in the wiring diagram, but I will add a power on/off toggle switch on the nav station panel. I will then be able to turn the AIS temporarily off when using the HF if interference is a problem.

Sounds good?

Thx, Pierre J.
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Old 07-10-2014, 08:18   #8
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Re: AIS and RF interference

I don't think they "share" at all. No splitter does. They turn OFF the AIS whenever there is VHF Tx or RX.

So when the approaching ship is getting so close in a crowded area, the time you need the latest AIS fix, some boof-head starts transmitting some long crappy Coast Guard bulletin. Or you are yabbering at the ships captain on the VHF and for the whole conversation, both ways, you don't get an update to see if course adjustments have worked.

For the cost of a $70 net antenna I now have two. One mast head and one stern rail. At sea the AIS is up top, in port the AIS is on the stern. Because at sea I need AIs at a longer range than VHF
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Old 07-10-2014, 08:29   #9
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Re: AIS and RF interference

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Originally Posted by MarkJ View Post
. They turn OFF the AIS whenever there is VHF Tx or RX.

Mmmm . . . . No . . . . At least with my splitter you can receive both ais and vhf simultaneously. The AIS is only turned off for vhf transmit.
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Old 07-10-2014, 08:53   #10
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Re: AIS and RF interference

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Mmmm . . . . No . . . . At least with my splitter you can receive both ais and vhf simultaneously. The AIS is only turned off for vhf transmit.
I am trying to remember my references. You may well be right and its just TXing. Its a while ago hat I went throught the whole splitter/seperate antenna issue.


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Old 07-10-2014, 09:00   #11
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Re: AIS and RF interference

Yes, splitters receive AIS and VHF simultaneously. They turn one or the other off for transmit. You would have to be talking non-stop for a very long time without releasing the TX key to miss a significant amount of AIS traffic or to prevent your AIS transmission.

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Old 07-10-2014, 12:40   #12
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Re: AIS and RF interference

I have heard AIS and LED interfere too, but I am yet to run a test for this.

Otherwise use VHF spacing patterns.

b.
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Old 07-10-2014, 21:43   #13
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AIS and RF interference

Pjazz,

Your plan sounds good. I think splitters are good for minimizing interference as they allow the VHF antenna to be at the masthead which is good. Splitters allow simultaneous reception on VHF and AIS. The good ones don't cause any loss in reception range. Depending on specifications there can be either little or a lot of loss on the transmit side. Check the specifications to be sure. You want 1dB or less attenuation in transmit mode and 0 dB attenuation in receive mode. Some splitters actually have gain in receive mode which can be helpful but not necessary.
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Old 08-10-2014, 11:31   #14
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Re: AIS and RF interference

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I have heard AIS and LED interfere too, but I am yet to run a test for this.

Otherwise use VHF spacing patterns.

b.
Yup, with a lot of the "drop in" led masthead bulbs there is significant RF noise, which cuts the AIS range by about half.

Some/many (but not all) of the dedicated led masthead fixtures eliminate this problem.
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Old 08-10-2014, 17:42   #15
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Re: AIS and RF interference

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Originally Posted by estarzinger View Post
Yup, with a lot of the "drop in" led masthead bulbs there is significant RF noise, which cuts the AIS range by about half.

Some/many (but not all) of the dedicated led masthead fixtures eliminate this problem.
I believe this may be the case in our ship. We have a top shelf, still drop-in, tri-color LED in a regular tri-color fixture.

I have seen our range anything from 13 miles to ... less than one mile. I have also seen a ship that I could see coming then disappear as soon as it passed by.

Now I am in port and there are countless ships with AIS on around us. I will do some testing and if I find anything constructive, I will post on the Forum.

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