More |AIS... interference with VHF

[Boomshanka]

Didn't want to detract from the other AIS posts tonight as I have a specific question... I fitted an EasyAIS and EASYsplit (VHF aerial splitter) today, all seemed to go well on the installation, switch on VHF and chartplotter and sure enough managed to get the AIS info showing nicely on the chartplotter (SH180i). However, I now have a constant 'hiss' on Channel 80 on the VHF which no amount of squelch will get rid of and the 'busy' sign comes up on the radio. When I touch the cable joining the spitter and AIS box, the hiss stops, I let go and it comes back! I checked the cable with a multimeter and there's no problems with continuity... does anyone have any idea what might be the problem...

As an aside... why does nothing in the marine industry seem to work first time? I brought a standard horizon radio and chartplotter thinking installation would be easier... both bits of kit have the same coloured wires (two for power, the others NMEA) and so logic would suggest just connecting them up like for like on the colours... ehm, no... different colours join together blah blah, aaaahhhhh... had to wait until about page 74 of the manual to find that out!

 

[EDM]

It sounds as though you are earthing the cable - if when you touch it the noise stops.

Is it just channel 80 there is hiss on - or all channels ?

 

[Boomshanka]

It's just channel 80 - which is my marina channel! When I say touch the cable, I mean the black plastic insulation not any metal parts (although the hiss stops when I touch the metal parts as well). The radio says 'busy' all the time as if someone else's PTT button is pressed all the time (I phoned the marina to confirm the channel was actually clear and it was.

I'm thinking to send the splitter back and go for a small (0.5m ??) vhf aerial on the pushpit for the AIS (which could be a back up aerial if the worst happened. I know this will reduce the range of pick up, but I feel uneasy about anything that could interfere with the VHF. It would be great if you had some ideas of what I might try to overcome the problem before I start to take it all out again.

 

[shmoo]

[ QUOTE ]

'm thinking to send the splitter back and go for a small (0.5m ??) vhf aerial on the pushpit for the AIS (which could be a back up aerial if the worst happened.


[/ QUOTE ]

Actually we find a full size one on the pushpit is not too much in the way. We get about 10 - 15NM on the NASA engine like that. That range is plenty: unless you are dealing with very fast ships they still come into view with TCPAs of about 30mins.

 

[wotayottie]

The idea of a second aerial is a good one IMHO. But there is a problem with your installation - touching the cable should have no effect. If you have made any of the terminal connections yourself you need to check them. Its very easy to get a single almost invisible thread of the coax outer bridging the plug for example. You also need to make sure that you have a good earth to all units ie a decent negative connection to all metal cases. try putting ferrite rings on the 12 v wires into the radio just in case the ch 80 signal is getting in that way.

If you still have the problem when everything is connected OK, it seems likely that you are picking up a stray harmonic on ch 80. Try operating all the kit but with only the vhf connected to the aerial. Still get the problem? Try shutting down the AIS engine, or the plotter. The splitter wont be emitting the harmonic istelf.

 

[Channel Ribs]

[ QUOTE ]
I'm thinking to send the splitter back and go for a small (0.5m ??) vhf aerial on the pushpit for the AIS (which could be a back up aerial if the worst happened.


[/ QUOTE ]

I can highly recommend this set up. Having a seperate antenna is by far the better plan.

 

[chrisbailey]

I am very happy with an arial on my pushpit and get more that sufficient range. this photo of my screen during the summer shows the Dover Straight with me about 10 miles out from Calais bound for Ramsgate and there are plenty of ships to be seen.

I am sorry that the image is not very sharp but it will give you an idear of coverage from a pushpit mounted arial which is not only cheaper than a splitter it is also a back up should the masthead arial for the VHF fail

 

[Boomshanka]

Went back to have another go today and tried all connections, removing bits of kit one by one, etc, same problem. All now back in the boxes ready for a return job. I'll retreat, regroup and then tackle AIS via a second pushpit based VHF aerial me thinks. Thanks for all the advice... it was reassuring to hear (and see) that a pushpit AIS aerial still gives a reasonable range.

 

[Oldhand]

1. I found the length of cable between an EasySplit and my VHF was critical, seems to cause a tuned circuit. I increased the cable length by 5 inches and all problems disappeared. I think the mistake EasyAIS make is not supplying this cable with the splitter. Get about 32 nm AIS range through the EasyAIS splitter with the masthead antenna.

2. You are not thinking when you go on about wire colours. If 2 pieces of equipment have the same wire colours for each function then for example, NMEA OUT +ve may be Green and NMEA IN +ve may be Blue. If you connect the Green wires together, NMEA communication will fail because you have connected OUT to OUT. If you connect the Blue wires together, NMEA communication will fail because you have connected IN to IN. To succeed you must connect OUT to IN so Green must connect to Blue. The application of a little common sense is all that's required, surely the manufacturers can make the assumption installers have a bit of that?