AIS caution

[iancymru]

Just read this and thought it maybe of interest.


USCG Marine Safety Alert 13-18 Potential interference of VHF-FM Radio and AIS Reception
Strong radio interference from LED sources may not be immediately evident to maritime radio users. Nonetheless, it may be possible to test for the presence of LED interference by using the following procedures:
1. Turn off LED light(s).
2. Tune the VHF radio to a quiet channel
(e.g. Ch. 13).
3. Adjust the VHF radio’s squelch control until the radio outputs audio noise.
4. Re-adjust the VHF radio’s squelch control until the audio noise is quiet, only slightly above the noise threshold.
. Turn on the LED light(s).
• If the radio now outputs audio noise, then the LED lights have raised the
noise floor. (Noise floor is generally the amount of interfering signals / static received beyond the specific signal or channel being monitored.)
6. If the radio does not output audio noise, then the LED lights have not raised the noise floor.
If the noise floor is found to have been raised, then it is likely that both shipboard VHF marine radio and AIS reception are being degraded by LED lighting.

[Trevor]

Hello all,

Just to add a little bit of research to the iancymru post about AIS. I used to be concerned about such things many years ago prior to my retirement. I have included photos of a graphical representation of the radio frequency spectrum without any LED light and then with a typical LED light switched on. The point is the interference signal is huge at the AIS frequencies. Just to outline this, one AIS frequency is 162.025Mhz and the marker on the spectrum analyser display is at 162Mhz.

The first picture below shows a baseline with no interference.
The next picture shows the spectrum with a LED light switched on.   The interference is horrendous.  This is an extreme case but many LEDs exhibit this form of wide band interference.  This can manifest itself while in a marina as being able to see Terrestrial TV services during the day but they are completely wiped out at night as LEDs are switched on in neighbouring yachts.   This is very common in Australia as the LED lights wipe out the VHF TV band (pretty well the same band as marine VHF radio and AIS).

The problem comes from the switching power supply used in the LED driver circuits to allow it to work at the same brighness under extreme voltage variations.   It is important when buying LEDs for your boat to specify that they must be Low RF interference type or sometimes denoted as Anti-RF type. They cost a little more but save a lot of hassle when trying to sort out the radio frequency interference problems.

This is a seldom spoken about subject and some Chinese manufacturers of many LEDs for marine use either don't want to go to the trouble of providing low interference LEDs or simply don't know or care about the problem.

Regards,

Trevor


 


Spectrum without interference




Spectrum with LED light interference

[rene460]

Hi Trevor,

Those are great shots from the spectrum analyser.  Thank you for posting them.

We purchased some early LED lights to replace some of the halogen bulbs originally fitted.  They seem to create that white noise on the FM radio spectrum.  I suppose a function of the components in that switching power supply, obviously a square wave form.

Fortunately we did not have many of that particular design, and could avoid using those lights when we were listening to the radio, so only a minor inconvenience.

But obliterating the AIS signal is a more worrying issue.

Rene460

[alenka]

LED/VHF interference has been known about for some time and when I replaced most of my halogens I bought those that to VHF friendly. You pay bit more than those you can get on eBay but!!!

[Don Reaves]

I realize this is an old thread, but I thought I would add a relevant bit of information...

I have installed a number of 5V USB plugs on my boat. These are very useful for charging the many smartphones, watches, cameras, etc that we seem to have collected over the years.

The last one I installed was located near the electrical panel. It’s interference makes the FM radio unusable for the weak signals we have in the area. I don’t think it affects the VHF or AIS, but will check next time I’m on the boat. The FM radio is particularly susceptible because it’s antenna is located behind the electrical panel, very near to the source of the noise.

We learned long ago that the factory-installed battery charger also affects FM, but since we don’t use it when we’re away from shore power, it’s affect on VHF and AIS hasn’t been an issue.

Don

[Trevor]

Hi Don,

Thanks for the that insight into the possibility of USB outlet interference. Since you have reignited the radio interference thread I believe my vessel is a massive radio interference generator. I enjoy HF radio, have an amateur radio license (ham) and often listen around the HF radio services. I also sometimes just tune into AM band commercial radio.

These are my observations.

1. All internal lights are "RF interference minimising type" but I have two powerful cockpit lights that wipe out VHF TV reception.
2. Water maker (Spectra Newport 400) creates awful HF radio noise.
3. Victron MPPT 50/100 solar regulator causes shocking whooshing noises during the day (when sun is up) on some HF radio bands.
4. Vitrifrigo fridge compressor controller causes very annoying HF radio noise on many bands.
5. Balmar digital duo charging regulator causes a very annoying pulsating noise level on medium wave AM services.
6. Inverters used to power two TV sets cause massive radio interference on HF bands.
7. Xantrex 1800 inverter causes massive interference on HF bands.

I now conclude that radio frequency interference used to be an engineering design criteria for equipment but is now not even thought about or considered. Consequently many of my systems are enormous noise generators. To use the HF radio I accept that I must switch power off from the water maker controller, turn off the Victron solar controller, switch off power to the TV sets, switch off the Xantrex inverter and turn off the fridge. None of these things are a big deal but the consequences of forgetting to turn the fridge back on could jeopardise my relationship with the admiral.

I feel I am floating around on a massive RF interference generator.

Regards,

Trevor

[johannes]

Aug 20, 2019 6:51:18 GMT Trevor said:

I now conclude that radio frequency interference used to be an engineering design criteria for equipment but is now not even thought about or considered.

It is required by law to keep RF interference below certain levels to put a CE mark on most electronics, but it is not really enforced and many manufacturers are sloppy about it.

[ForGrinsToo]

Aug 20, 2019 6:51:18 GMT Trevor said:

I feel I am floating around on a massive RF interference generator.

Regards,

Trevor

Yup. I haven't carefully investigated the effectiveness of the clip-on RF chokes. It seems to me that they are needed for just about every device and almost none include them, though my Standard-Horizon VHF did. It would be helpful to determine what RFI is carried on the DC lines compared to what is radiated.

Geoff

[martie]

Aug 20, 2019 11:41:00 GMT johannes said:

You should also be aware when importing direct from China the CE mark means "China Export".
The logo is slightly different from the "original" CE mark and is more or less useless.