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LEDs interfere with radio


Top cat

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Our motley collection of elderly LED bulbs cause interference on the FM radio after dark. It seems to be picked up by the speaker leads that run to the back of the boat in the same conduit as the light wiring (its the only way I can do it)

I see that Bedazzled are offering EMI free leds but at 10x the price of eveyone else. Now i know he has in the past made a big deal over what is standard.

Does anyone know of another more reasonably priced source of non interfering LEDs or are all modern ones radio friendly.

It would be cheaper to fit a second radio at the rear of the boat than buy 6 bulbs from Bedazzled.

Any other ideas on stopping the interference wouldbe most welcome

 

Top Cat

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I am not sure, but will be interested in the reply.

 

We are all on 2D florescents, partly as it was the technology at the 25 years ago, but also because the give a warmer light so as it works I have simply replaced like for like. However the radio does not like the battery charger running, if we are on dock or the like.

 

Same deal with just lots of noise, which I presume comes in via the power lead due to the pwm/ripple on the charger output. Expect the LEDs power supply is the same.

 

 

Daniel

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It's not the LEDs themselves that cause the interference, it's the electronics that drive them. Most LED lamp suppliers use the same LEDs but there is a range of different electronics. Bedazzled have their own suppliers of electronics but I don't know if any others use the same ones. Their lamps certainly seem better than the others in regard to interference to FM radios but don't seem to be much better than others for DAB radios.

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Some LED bulbs (the cheapest ones) use resistive droppers. They don't create interference but they may overheat if the voltage is high e.g. whilst engine is running.

 

LEDs that are tolerant of voltage have switch mode power supplies (SMPS) to regulate the voltage. These can be a source of interference if badly designed.

 

Trouble is, I'm not sure how you can tell the badly designed SMPSs from the good ones. Retail price may not be a good guide.

 

Possibly, and if you are good with a soldering iron, you could fit a high frequency capacitor to the LED's pcb at the supply connections, something like 0.01 microfarad hf ceramic might do. This might help, but eliminating rf interference can be a bit of a black art.

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You could try changing the speaker leads to twin screened wires, earth the screen. This should work if it is radiated fields from the LED lamp electronics.

Or you could try screening the lamps and earthing them, but I think the interference is getting into power supply so this may not work.

Also put a filter in the supply to the radio, or run it from a separate battery.

  • Greenie 1
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Thanks for the suggestions guys.

 

Since posting my question I've been fiddling about swapping the LEDs round in their sockets and have come up with a combination that works.

It seems that if I move the later higher powered LEDs away from the radio and replace them with earlier lower powered types the interference goes away. But I can still use the ones that used to cause interference further back in the boat, which is odd as the speaker wires run full length. One theory is the distance between speaker and lighting wires varies.

One of the problematic LEDs was Ok when first plugged in but started to create interference after a few minutescas it warmed up. Others of the same type did it from cold.

 

Prior to all this I tried putting ferrite rings on both the power and speaker leads with no effect.

 

I'm starting to suspect that my aerial has connection problems. Its is a rubber duck bolted to the roof just a few feet away from the radio on the front corner of the roof. In the past I have found a lot of corrosion there. Having seen but not fully understood comments about not grounding aerials I'm wondering about mine which probably had a poor ground connection (worst of both worlds?)

Any advice on the correct way to install an aerial would be much appreciated.

 

Top Cat

Edited by Top cat
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Trouble is, I'm not sure how you can tell the badly designed SMPSs from the good ones. Retail price may not be a good guide.

Indeed

Possibly, and if you are good with a soldering iron, you could fit a high frequency capacitor to the LED's pcb at the supply connections, something like 0.01 microfarad hf ceramic might do. This might help, but eliminating rf interference can be a bit of a black art.

 

Or you could try screening the lamps and earthing them, but I think the interference is getting into power supply so this may not work.

 

Also put a filter in the supply to the radio, or run it from a separate battery.

 

I will not pretend to know anything about electronics. But I would be looking for things I could do to either stop the noise getting from the lamps back to the battery/disboard, or isolate the radio from it, rather than open either of them up.

 

 

 

Daniel

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Thanks for the suggestions guys.

Since posting my question I've been fiddling about swapping the LEDs round in their sockets and have come up with a combination that works.

It seems that if I move the later higher powered LEDs away from the radio and replace them with earlier lower powered types the interference goes away. But I can still use the ones that used to cause interference further back in the boat, which is odd as the speaker wires run full length. One theory is the distance between speaker and lighting wires varies.

One of the problematic LEDs was Ok when first plugged in but started to create interference after a few minutescas it warmed up. Others of the same type did it from cold.

Prior to all this I tried putting ferrite rings on both the power and speaker leads with no effect.

I'm starting to suspect that my aerial has connection problems. Its is a rubber duck bolted to the roof just a few feet away from the radio on the front corner of the roof. In the past I have found a lot of corrosion there. Having seen but not fully understood comments about not grounding aerials I'm wondering about mine which probably had a poor ground connection (worst of both worlds?)

Any advice on the correct way to install an aerial would be much appreciated.

Top Cat

I'm not a great aerialist but rubber duck aerials normally have inherent attenuation - but don't require a ground plane. Aerials that require a ground plane can be accommodated by connecting the lead's screen to the hull, but by means of a small capacitor so that there is no DC path.

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Thanks Nick, I have capacitors in stock I will try that when I get home tomorrow.

T C

Just be aware that all capacitors are not made equal! Some capacitors are optimised for high capacitance (electrolytics etc) but they have high intrinsic inductance that makes them absolutely hopeless at high frequencies. As a general rule, low value capacitors (ceramic, plastic film etc) tend to be best at radio frequencies.

 

What I am saying is that you can't just use any old capacitor, you have to use one that has a low ESL (equivalent series inductance) aka a low equivalent series resistance at the sort of frequencies we are talking about (200MHz)

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Just be aware that all capacitors are not made equal! Some capacitors are optimised for high capacitance (electrolytics etc) but they have high intrinsic inductance that makes them absolutely hopeless at high frequencies. As a general rule, low value capacitors (ceramic, plastic film etc) tend to be best at radio frequencies.

 

What I am saying is that you can't just use any old capacitor, you have to use one that has a low ESL (equivalent series inductance) aka a low equivalent series resistance at the sort of frequencies we are talking about (200MHz)

.01uf ceramic should do it. AKA 'a little brown number'.

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The very high value capacitors woulf be around 100 picofarads. However, all my radios are vacuum tube receivers and the frequencies tend to be on the Kilocycle range. On my Fifties sets the AF capacitors are very often about 0.1mF. And the voltages are high.

I have RF ground done as it was by homeowners in the Forties. A stake in the ground with wire.

I cannot use halogen lights or the signals get swamped so I use a lamp. And I must say it easily beats modern radio. If you want the best radio ever you need a German made late Fifties model. Sound is in another league.

My oldest set is 1947 and still going. Purists frowned on my using Film capacitors but for me it's not an issue.

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I would have thought that the speaker leads are the least susceptible part to interference, although I wouldn't personally have them running the full length of the cabin. You can do a quick check; if the interference gets louder as you turn the volume up, then the problem is upstream of the power stage (aerial or input stage) & not the speaker leads. If the interference noise stays constant, then it could be the speaker leads but I reckon more likely the power supply leads.

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I traced it to the speaker leads by disconnecting them ( there is another set going to the front speakers) and the interference went away. Tomorrow I will try powering the radio from a different totally isolated battery.

I've noticed also that if we are in a poor signal area reception is affected by where I'm standing in the cabin, seeming at its worst when I'm about 3 foot away. If I place my hand on top of the cupboard the radio is installed in the front of it gets better. Odd.

Does this indicate an aerial issue ?

 

Top Cat

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Difficult to say. Certainly the aerial doesn't sound great (you mentioned corrosion around the base) but the speaker wires inducing interference and passing that to the radio internals might not be related to that.

 

A twisted pair has recently been mentioned with regard to a battery monitor - it may well be that a twisted pair of speaker leads could help you.

 

Tony

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I would have thought that the speaker leads are the least susceptible part to interference, although I wouldn't personally have them running the full length of the cabin. You can do a quick check; if the interference gets louder as you turn the volume up, then the problem is upstream of the power stage (aerial or input stage) & not the speaker leads. If the interference noise stays constant, then it could be the speaker leads but I reckon more likely the power supply leads.

Speaker leads are notoriously susceptible to picking up radio interference because they often have a feedback path back into the early stages of the audio amplifier

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This topic is also being discussed in another mailing list I follow, the WS19 group, although in relation to H.F. , rather than V.H.F..

Current thinking is that a lot of LED lights shouldn't have received C.E. approval, (NOT China Export! :) )

 

They're still looking for a solution, and they include some very clued up radio operators!

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I've just realised that my moonraker dtv1000 aerial can also pick up VHF signals ( well the spec claims that it does) . So tomorrow I'm going to try it with a duplexer in the lead to feed TV and radio off of it.

 

I pulled the old aerial apart and found slight corrosion in the both connections, cleaned it up and gave it a coat of "Liquid electrical tape". Doesn't seem to have made much difference, but it's hard to tell as reception varies .

 

Top Cat

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I've just realised that my moonraker dtv1000 aerial can also pick up VHF signals ( well the spec claims that it does) . So tomorrow I'm going to try it with a duplexer in the lead to feed TV and radio off of it.

 

I pulled the old aerial apart and found slight corrosion in the both connections, cleaned it up and gave it a coat of "Liquid electrical tape". Doesn't seem to have made much difference, but it's hard to tell as reception varies .

 

Top Cat

Just aside, I'm being lazy I know, but is the dtv 1000 directional?

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Sorting RF interference is a black art.

 

I think TC in your position the first thing I would do is fit a ferrite choke to each of the LED supply cables close to the lamp. If it is truly a pickup on the speaker cables there has to be a bad connection or similar to rectify the RF down to audio levels. I would suggest that a check of every speaker connection for a bad connection and remaking every one. If they are crimped I would suggest a remake and a tinning with solder.

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