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Old 24 July 2015, 20:24   #1
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Country: UK - Scotland
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VHF vs LED lights

http://youtu.be/JMsoflt6thU

Weird. Must be a suppression issue or something. Never happened in 9 years with the boat but then we hardly use the floor lighting, everybody knows where the nearest exit is!

Doesn't do it with anything else on the boat. Will look in more detail tomoro!
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Old 25 July 2015, 03:02   #2
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Not as uncommon as you might think...
One of our vessels is fitted with 4x forward facing 100w led floodlights. Two of the floodlights are withing a couple meters of one of the vhf antennas and the other two are well clear.
The two floods closest to the antenna actually increase in brightness and intensity when the vhf is transmitting. This is very noticeable and has even been commented on by other vessels.
In our case it is the vhf affecting the LED's but as you have found out, there's definately a link the other way also.
I originally figured it was a certain frequency being emmited in the light spectrum of the LED's which was 'bleeding over' into the VHF range??

Simon
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Old 25 July 2015, 03:06   #3
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Suspect there is a Buck Driver that regulates the LED current (standard small LEDs on control panels use resistors, but big LEDs for lighting often use a switched mode power supply to regulate current as its more energy efficient than installing a big resistor which would just waste energy like a standard filament bulb does.

Snag with Buck convertors is the cheap ones chuck out a load of interference...
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Old 25 July 2015, 03:22   #4
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It will likely be the LED driver(s). Is the light control just on/off or does it have a dimmer function?

Often LED drivers use a technique called PWM (pulse width modulation) which generates electrical noise at a harmonic frequency of the VHF frequency. It is a black art to resolve - it may be radiated by the driver and picked up direct by the VHF aerial, radiated by the driver into other wiring on the boat that then acts as an antenna, or conducted by the driver into the LED wiring making the LED wiring act as an antenna.

You need to try and establish which form of propagation is happening. Maximum separation between interference source and VHF aerial is good. Seprating the drive from the LED wiring, or splitting the wiring may also help to pinpoint the problem, Ferrites on any wiring causing the problem may help, but you really need a box of ferrites and patience to see what works via trial and error.

On the plus side at least it is an obvious fault - I have had interference issues where a power supply knocked out the IF stage of a VHF - end result the radio wouldn't receive weak signals, but all testing on the VHF showed no fault. I hate EMC issues .

Cheers

Chris
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