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Radio interference from lighting circuits.

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  • Radio interference from lighting circuits.

    Folks I have had 2 people contact me recently about LED lights specifically for landing lights which are causing significant radio interference to their comms systems. Initial investigations are leading to the LED circuitry within these lights which use PWM (pulse width modulation) to turn the lights on and off VERY fast. This is used to reduce the power they use and to protect them from overheating and destroying themselves. Unfortunately this switching is causing significant noise to be induced into our AM radios. It would seem at the moment that the units which will work off voltages between 12 and 48v are the worst offenders. I/we are keen to hear of any members who have a particular model which seems to work for them as these lights are generally very bright and efficient in terms of power.
    An easy check is to use a handheld aviation radio with the squelch turned down or off so that all of the crackle and background noise is audible. (this method is also useful for fault finding faulty ignition leads and plugs as well!) One of our members has a LED unit which runs only on 12v (a reversing lamp) and is only emitting noise up to 50mm away from it where as another unit is emitting noise when connected to an independent battery some 4 metres away.

    The issue is that this noise or interference is spread neatly across our aviation band of frequencies. If I get enough interest I will investigate further and endeavor to design an in line filter to remove the interference.

    STROBE lights.
    A lot of machines are using the the common and easily available SC103 strobe lights (100mm high circular with aluminium/white plastic base) which also produce an intermittent burst of hash in the headphones. I have reduced this by using shielded power cable between the strobe and a point on the power bus away from the avionics circuitry.

    Over to you.

    Last edited by chook; 31-05-2017, 12:42 PM.

  • #2
    Your a good man Chook👍


    • #3
      I am one of the guys who contacted Chook.
      The light I had purchased was a 'cheap' light bar from E-bay.
      The light worked, produced enough light and was not draining the battery (previous halogen lights, as soon as the lights were turned on, the voltage dropped dramatically)

      I did take the light bar to a fellow in town. He turned his service monitor on , and under normal conditions it was registering very little interference (-70 dbm),
      with the light on, it was 14dbm in the 76 to 180Mhz range. This interference the radio thinks is a signal to pick up (radio starts receiving and you just hear a LOT of static. (very quickly turned the lights off again. Click image for larger version

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      Attached Files
      Last edited by RossM; 17-06-2017, 07:06 PM.
      Remember: no matter where you go, there you are


      • #4
        sounds like a bit of backing form asra would show up as being proactive leaders in the gyro world.
        chook goes out of his way helping fellow gyro-naughts and the led problem will be the way of the future for sure. what say yea Mr President. . ?????


        • #5
          Not quite sure what you mean Tony???? ASRA is always keen to help out when it comes to pilot/ builder education. We are currently looking at the possibility of running TA workshops around the country. We will however require some financial help from CASA and support from the likes of Bert Flood and of course our members.


          • RossM
            RossM commented
            Editing a comment
            Tony is always looking to sponsor someone

        • #6
          Hmmm well next time I fire up the chopper I'll disconnect the power wire to the strobes on it, as after reading this, there has always been something real funny with the radio on it, you can set the squelch normal then a minute latter you need to up it again and again and again un l it is only about 3 mm off full squelch to stop the white noise. Very interesting chook, keep you posted


          • #7
            As a result of this article another gyro pilot contacted me to say that his over $100 pair of LED lights was doing exactly the same thing.

            There are many power supplies available in computers, mobile phone chargers and most domestic electronics that don't cause this interference because they have been correctly designed to acceptable international standards but probably the most telling thing here is that our aviation communications use the AM radio band. This form of transmission has been replaced moreover with the FM band where this type of interference is much less of a problem.

            Tony thank you for your offer of assistance but I will quietly peck away at this problem and release the result free for anyone to use. The main issue is available time for me at the moment (who said retirees had plenty of time?)

            So at this stage the quick fix would be from someone who is using one of these LED lights on an aircraft and who is not experiencing this interference problem. Obviously we would require a model number and a description of their particular application (eg landing light). After a period of time (say 2 months) if I have not heard of a fix and this topic is still active I will endeavor to design a broad band filter that can be placed in the power line feeding these LEDs which will kill the interference.


            Last edited by chook; 04-06-2017, 01:48 PM.


            • #8
              Another one I have come across recently is the cigarette lighter to USB charger for phones and tablets. I have a factory turbo 100 series Cruiser and when I plug in mine to the cigarette lighter it makes buzzing sounds through the radio but when I plug it into the accessories socket right next door the radio doesn't buzz. Don't know why but I just leave it in the accessories socket.


              • #9
                Yeah these LEDs have either step up or step down voltage oscillator circuits pending on the application. My first observation was led lights in a solar powered house on a farm and trying to listen to AM radio was torture. Why AM because its Amplitude Modulation receiving and the LED is Emitting Electro Magnetic interference radiating by same amplitude modulation by the little voltage oscillator circuit. The strobe circuit is similar as it has a high voltage oscillator circuit that excites the Xenon gas tube and causes the bright illuminate as a flash. This circuit need some caution if handling as it can deliver a nasty high voltage shock. I have had a hit from it years ago and believe me it sent me into next week, and it wasn't fully charged at the time the circuit hadn't fully discharged as i thought it was.Shielding to earth and inline voltage filters is about all you can do. There are regulations about EMF that these lights probably not complaint or meeting the standards. Difficult to apply these days as about every thing is imported without inspection.


                • #10
                  I have bought 2 lights from Jaycar. part # SL3930

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                  you can get flood beam as well, part SL3932

                  I borrowed a hand held radio and tested in store. These lights do not make any interference on the radio. I also took to the fellow in town and tested on his service monitor, and there was no detectable interference.

                  Jaycar buy these lights from TechBrands.
                  If you have an ABN, you can buy from Techbrands (If you are a registered company, manufacturer, service agent, reseller or any organisation purchasing product in commercial quantities you may be eligible for wholesale prices. To find out if you are eligible contact us on 1300 738 555 or by email.)

                  I also tested some other lights in Jaycar , i think they were these lights, but these made noise on the hand held radio
                  (or Techbrand site )
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                  The lights that I did buy come with the tick in a circle that is inside a triangle.
                  Chook will probably tell you that these lights conform to a standard (cannot remember the name) and should not cause EMI (interference )
                  The dimension as stated on the TechBrand site say they are 100mm high , that is including the bracket. you
                  Remember: no matter where you go, there you are


                  • #11
                    from techbrand web site, SL3930

                    Super tough and compact LED spot/floodlights which can be bolted onto your 4WD, boat, car, off-road buggy or even for security use. Features a die cast aluminium alloy heatsink housing with an unbreakable polycarbonate front cover. Thanks to the deep optic reflector lens, the beam length on these lights is incredible for the lumen output. The spot light model can almost reach half a kilometre! Inside each model is a single next-generation 25W Cree MT-G LED, driven by high end PWM driver circuitry that protects the LED from over temperature and extends the operating life. Includes reverse polarity protection in case you make a junior error when wiring up! Sold individually.

                    - IP68 waterproof
                    - Shock proof
                    - 50,000 hour life
                    - Instant ON/OFF

                    - Beam pattern: Spot
                    - Beam distance : 490m
                    - Lumen output: 1733
                    - Equivalent halogen lamp: 200W
                    - Operating voltage: 9-36VDC
                    - Operating temperature: -40°C to + 60°C
                    - Dimensions: 86(W) x 100(H) x 93(D)mm

                    (86mm wide is the diameter of the light.
                    They also come with a waterproof connector on the light,
                    so, you get the light, 250mm of power lead, then the waterproff power connector, and 250mm tail on the power side on the connector
                    Remember: no matter where you go, there you are


                    • #12
                      As I said before,
                      theses two lights do not cause interference over the radio, though these lights are soon to be discontinued
                      (retail for $69, just over $50 if you have a ABN and set up an account, plus postage (not sure of minimum order value)

                      From Techbrands QLD rep, the blow links should not cause interference (as always, best to try for yourself)


                      And, as I said before, these lights cause interference.

                      Remember: no matter where you go, there you are