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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems > FM stereo interfence, Sensibulb LEDs and 12V Jacks
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Thread: FM stereo interfence, Sensibulb LEDs and 12V Jacks Reply to Thread
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Topic Review (Newest First)
03-16-2012 08:56 PM
josrulz
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

Thanks hellosailor. The verdict is in. It appears to be RFI. I got interference from all the Sensibulbs on my FM portable radio. The radio was plugged into AC, but not the boat's AC. The boat was not plugged in at all, and my radio was plugged to a shore-based extension cord. Each Sensibulb appeared to interfere at different frequencies, but they all did it. I'm not referring to just a little background static--I'm talking about going from listening to music to static when I turn the light on.

I'm a bit disappointed in the Sensibulbs. They have a good reputation for low RFI. Maybe I got a bad batch? I'm going to have to ask for my money back, unless the manufacturer can offer a solution. Bummer.

On a side note, I got either none or negligible RFI interference from the MarineBeam lights.
03-16-2012 03:56 PM
hellosailor
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

AC with an extension cord, totally isolated from the boat's electrics, ought to work. AC can bring in other noise sources, battery radios used to be easy to find. And easier to move around, up close to other devices to see which is the culprit.
03-16-2012 03:03 PM
josrulz
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

Hellosailor, for the purposes of this test, could the "other" radio be AC powered, from a power source not connected to the boat? Or is there some reason it would need to be battery powered?

Thanks!
-J
03-14-2012 09:50 PM
josrulz
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

Thanks everyone.

Hellosailor, that sounds like a great place to start. I have a battery-powered radio I can bring out easily to see if I still get the interference.
03-14-2012 09:31 PM
hellosailor
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

-
Phone chargers are some LED control circuitry are digital circuits these days, and they can make noise. If the noise if RFI, radio frequency interference that is broadcast through the air, that's hard to stop. If it is EMI, electromagnetic interference that is being carried out on the power lines, it can be easily filtered out.

Simplest way to tell which it is, is to bring another battery powered FM radio into the boat. Since that is not connected to the same power leads, it will have no problem if the interference is EMI. In which case you put noise filters on the radio's power branch, and on the ones to the charger and cabin lights as well. Those filters can be simple "noise filters" that you pick up at an auto stereo shop, or sometimes just 10mF capacitors will do the job well enough. (25c or so each?)

If the separate radio stills gets interference, it is RFI and you have to stop that at the source. A better charger and different lights might be called for, or moving the FM radios antenna further away from those noise sources.
03-14-2012 04:51 PM
redline
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

I have a similar situation with the 12V power supply for an XM MyFi satellite radio, which contains a very (electrically) noisy switching power supply. The situation is even worse if I use the hardware audio connection to Line-In on the stereo, despite several attempts at filtering. In other words, you may need more than a few loops through a ferrite.

Once upon a time car stereo shops had L/C (inductor/capacitor) filter assemblies to suppress alternator whine and such; you might have some luck with something like that if the ferrites aren't enough. Some info (and a caution on filters) can be found at http://www.carstereo.com/help/Articles.cfm?id=71

Apparently my high-frequency hearing is still pretty good, because several guests 10 years younger than I don't notice the whine, which my wife and I find intolerable. For now the workaround is to use the MyFi's internal FM-modulator to feed the radio tuner, but that's a compromise in quality and necessitates scanning and picking a new frequency as we move from place to place.

Next step will be more aggressive filtering, more direct power grounds (currently radio and accessories take their negative from the small busbars on the back of the breaker panels nearest their breaker). I think a heavy-duty common negative rail before the panels' pigtails would avoid some common-rail noise from running each "ground" all the way up to the breaker and back. I may try a pair of small 600-ohm audio transformers on the Line-In to determine if the noise is indeed coming in on the LineIn shields, vs power supply ground.
03-13-2012 03:00 PM
josrulz
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

Thanks Mark. I'll give it a shot.
03-13-2012 01:56 PM
MarkSF
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

Quote:
Originally Posted by josrulz View Post
The antenna cable looks like any standard antenna cable I've seen in a car or on a boat. That should be shielded, yes?

There are no ferrite cores installed on any of the stereo, if I recall correctly.

Certainly worth a try.
Yes it should be shielded. Mine just has a thin piece of ordinary wire for an antenna.

So what you do is take both the live and ground wire, pass them through the hole in the middle of the ferrite, then wrap them several times around the ferrite.

Like the top picture here but more wraps : Filtering Out Interference Signals with Cable Ferrites
03-13-2012 01:37 PM
josrulz
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

The antenna cable looks like any standard antenna cable I've seen in a car or on a boat. That should be shielded, yes?

There are no ferrite cores installed on any of the stereo, if I recall correctly.

Certainly worth a try.
03-13-2012 01:31 PM
MarkSF
Re: FM stereo interfence, Sensibulb LEDs and 12V Jacks

Your radio sounds sensitive to noise. On which lines, I don't know, but maybe the power supply wires - GND and 12V.

Does it have a shielded antenna cable or just a wire stuffed into the antenna socket (as mine does)? If the latter, switch to the former.

You could try putting a ferrite on the power supply wires, as close as possible to the radio.
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