NMEA causing noise on VHF

[Cardo]

So as part of my Raspberry Pi wiring fun I've also redone a bunch of the NMEA stuff. My VHF, which was previously wired up only to a stand alone GPS unit is now connecting to the 4800 NMEA ports on my AIS, which is in turn connected via 34000 NMEA to the Pi.

Unfortunately, I've now found that the VHF is receiving a lot of noise and I have to turn the squelch to around 3/4 up just to get rid of the noise. This seems a tad excessive! I'm using proper twisted pair, shielded cables.

Any thoughts on how I could try and sort this? I have a bag full of ferrite thingies, which I'll admit I haven't tried, yet.

 

[lustyd]

So as part of my Raspberry Pi wiring fun I've also redone a bunch of the NMEA stuff. My VHF, which was previously wired up only to a stand alone GPS unit is now connecting to the 4800 NMEA ports on my AIS, which is in turn connected via 34000 NMEA to the Pi.

Unfortunately, I've now found that the VHF is receiving a lot of noise and I have to turn the squelch to around 3/4 up just to get rid of the noise. This seems a tad excessive! I'm using proper twisted pair, shielded cables.

Any thoughts on how I could try and sort this? I have a bag full of ferrite thingies, which I'll admit I haven't tried, yet.

I have no advice but just wanted to say hopefully it goes without saying you should test this while not on channel 16, and should turn off as soon as you get interference rather than try to squelch it out just in case you're affecting other sets.

 

[Cardo]

I have no advice but just wanted to say hopefully it goes without saying you should test this while not on channel 16, and should turn off as soon as you get interference rather than try to squelch it out just in case you're affecting other sets.

I'm a bit confused. If I'm not transmitting, why would it affect other sets?
Also, why not channel 16?

 

[lustyd]

I'm a bit confused. If I'm not transmitting, why would it affect other sets?
Also, why not channel 16?

Channel 16 is for emergency. How certain are you that you're not transmitting? I had almost identical issues with my sets a while ago and between them the devices managed to find a way to transmit on their own, confirmed by the coastguard. Separately the devices did not do this but I assume a fault in one of them was causing a transmission when NMEA was connected in a certain way.

Given that lives depend on this system the simple answer is don't take any risks at all. If you're having problems, leaving those problems happen won't help you to identify them so turn the set off. If you're getting interference then step one would be change channel and see if other channels exhibit the behaviour, if they do the problem is definitely you. Next step is get a completely separate device to see if you're causing outside issues but until you are absolutely certain you're not causing outside interference then turn it off - that's why radio devices are so heavily regulated.

 

[lustyd]

Or whatever your local emergency channel is, of course

 

[AngusMcDoon]

I had almost identical issues with my sets a while ago and between them the devices managed to find a way to transmit on their own, confirmed by the coastguard.

If you have a VHF radio that starts to transmit when it receives interference from data lines it has a seriously faulty design! Part of the regulation you mention is compliance with EMC which is to do with electrical interference. There are 2 parts - a device must not cause electrical interference, and also it must accept it without failure. Your radio obviously isn't, so how it ever received a CE mark I don't know. Perhaps, given that lives depend on your system, you shouldn't take any risks and replace it with a more robust model. How do you know it isn't continually transmitting randomly on channel 16?

 

[AngusMcDoon]

So as part of my Raspberry Pi wiring fun I've also redone a bunch of the NMEA stuff. My VHF, which was previously wired up only to a stand alone GPS unit is now connecting to the 4800 NMEA ports on my AIS, which is in turn connected via 34000 NMEA to the Pi.

Unfortunately, I've now found that the VHF is receiving a lot of noise and I have to turn the squelch to around 3/4 up just to get rid of the noise. This seems a tad excessive! I'm using proper twisted pair, shielded cables.

Welcome to the wonderful world of EMC! Here be dragons, black magic, soothsayers and outrageously expensive test kit.

 

[AngusMcDoon]

I'm a bit confused. If I'm not transmitting, why would it affect other sets?

I would also think it highly unlikely you are causing your radio to start transmitting and the interference range will be within the confines of your boat.

 

[Cardo]

Welcome to the wonderful world of EMC! Here be dragons, black magic, soothsayers and outrageously expensive test kit.

Thanks

 

[AngusMcDoon]

Thanks

If using shielded cable try grounding the shield at one end.

 

[lustyd]

How do you know it isn't continually transmitting randomly on channel 16?

Because I disconnected the handheld radio (NMEA source) which was causing the issue. I never said it was definitely an issue, I simply said to be careful and gave a couple of simple tests to determine whether it is a problem. I'm not the only one to have suffered this, Chrissie posted a similar story a while ago although I'm uncertain of the cause in her case but her radio was definitely transmitting too. She was replying to someone else with similar symptoms so it's clearly not as rare as you think it is (I do know you're an expert)

 

[AngusMcDoon]

I'm not the only one to have suffered this, Chrissie posted a similar story a while ago although I'm uncertain of the cause in her case but her radio was definitely transmitting too. She was replying to someone else with similar symptoms so it's clearly not as rare as you think it is (I do know you're an expert)

For any VHF radio to start transmitting on its own for any reason, whether interference or switch failure, is such a serious design fault that I think that it would be worth reporting it to trading standards if it is a recent model so they can be recalled and replaced.

 

[lustyd]

For any VHF radio to start transmitting on its own for any reason, whether interference or switch failure, is such a serious design fault that I think that it would be worth reporting it to trading standards if it is a recent model so they can be recalled and replaced.

It was two Standard Horizon sets in my case which only had a problem when wired together, and possibly then only with my wiring. I don't have the time to chase it up because I'm certain that they are fine on their own otherwise I'd take them in to the Winchester office for service.

As I said, all I was trying to do was suggest tests to check this and to be certain it's not causing problems for others. I don't see why that's such an issue?

 

[David2452]

If using shielded cable try grounding the shield at one end.

At the talker end and only the talker end.

 

[Cardo]

So, I've managed to get this sorted. Turned out to be a problem with the routing of the VHF antenna cable. I followed its route and it was bunched together with various cables, including sizeable power cables. These were clearly creating interference on the cable. I'd imagine the VHF cable has been there since day 1, but various other electronics have been added and routed together over time. I've added a few extra bits myself, which has over time made things worse and worse.
Bit the bullet yesterday and rerouted the VHF cable, running it away from other cables as best I could.
Problem solved!
Even with _everything_ switched on, I only need to turn squelch up about 1/3 to get rid of the noise, which seems perfectly reasonable to me.

 

[lustyd]

So, I've managed to get this sorted. Turned out to be a problem with the routing of the VHF antenna cable. I followed its route and it was bunched together with various cables, including sizeable power cables. These were clearly creating interference on the cable. I'd imagine the VHF cable has been there since day 1, but various other electronics have been added and routed together over time. I've added a few extra bits myself, which has over time made things worse and worse.
Bit the bullet yesterday and rerouted the VHF cable, running it away from other cables as best I could.
Problem solved!
Even with _everything_ switched on, I only need to turn squelch up about 1/3 to get rid of the noise, which seems perfectly reasonable to me.

You've also probably just explained why I had to turn my squelch up the other day. I installed a new chart plotter next to the VHF on the antenna cable side. I though it was odd that I had to turn squelch up for the first time ever!

 

[testmonkey]

You've also probably just explained why I had to turn my squelch up the other day. I installed a new chart plotter next to the VHF on the antenna cable side. I though it was odd that I had to turn squelch up for the first time ever!

how about adding some snap-on ferrites to all instrument power and NMEA cables plus fridge, LED lights etc. - would that have any positive effect or just waste of time?

 

[lustyd]

how about adding some snap-on ferrites to all instrument power and NMEA cables plus fridge, LED lights etc. - would that have any positive effect or just waste of time?

I suspect that installing it in less of a slapdash manner will probably solve the problem in my case, I was busy sailing so I just bunged it in and have yet to even screw it down

 

[Piers]

So as part of my Raspberry Pi wiring fun I've also redone a bunch of the NMEA stuff. My VHF, which was previously wired up only to a stand alone GPS unit is now connecting to the 4800 NMEA ports on my AIS, which is in turn connected via 34000 NMEA to the Pi.

Unfortunately, I've now found that the VHF is receiving a lot of noise and I have to turn the squelch to around 3/4 up just to get rid of the noise. This seems a tad excessive! I'm using proper twisted pair, shielded cables.

Any thoughts on how I could try and sort this? I have a bag full of ferrite thingies, which I'll admit I haven't tried, yet.

Hi Cardo. I am advised by an electronics researcher that any equipment that does not the meet IEC-60945 standard of emission (Maritime Navigation and Radiocommunication Equipment and Systems – General Requirements – Methods of Testing and Required Test Results) runs the risk of interfering with Marine VHF, and in particular with ch16.

With the prevalence of laptops, iPads etc, more and more people are finding the squelch has to be turned up more and more to styop the interference which in turn reduces the sensitivity of receiving calls, and I this case, distress calls.

So I'd look to the kit rather than the nmea. A simple test would be to turn all kit off (except the radio) and turn items on 1 by 1 and see which causes the issues.

Hope this helps....

 

[Cardo]

Hi Cardo. I am advised by an electronics researcher that any equipment that does not the meet IEC-60945 standard of emission (Maritime Navigation and Radiocommunication Equipment and Systems – General Requirements – Methods of Testing and Required Test Results) runs the risk of interfering with Marine VHF, and in particular with ch16.

With the prevalence of laptops, iPads etc, more and more people are finding the squelch has to be turned up more and more to styop the interference which in turn reduces the sensitivity of receiving calls, and I this case, distress calls.

So I'd look to the kit rather than the nmea. A simple test would be to turn all kit off (except the radio) and turn items on 1 by 1 and see which causes the issues.

Hope this helps....

Whilst I appreciate the response, it's a little late!

Of interest, the worse offender was the Fusion marine radio. As soon as I turned this on, squelch had to be turned right up. No amount of ferrites, praying to the gods or naked interference dances seemed to solve it.
Until I moved the antenna cable away from it all, now it's great.