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Ashman
27-03-14, 15:09
I've recently changed my tri-light filament bulb to a Boatlamps' tri-colour LED but I've noticed that when I switch it on all the AIS targets disappear off my chart plotter.

I'm using a Digital Yachts transponder via a splitter on a VHF antenna that is sited about 250mm from the led bulb. Other yachtsman have told me that my AIS transmissions are OK but its getting very irritating to turn off my tri-light every hour to see if other vessels are in range. I've now noticed my LED masthead anchor light is having the same effect.

I guess this might be a common problem but can anybody suggest a simple solution other than changing back to a conventional filament bulb or moving the antenna?

Apologies if this subject has already been done to death but I'm out in the Cape Verdes and megabytes are too expensive to permit much research!

sailorman
27-03-14, 15:11
I've recently changed my tri-light filament bulb to a Boatlamps' tri-colour LED but I've noticed that when I switch it on all the AIS targets disappear off my chart plotter.

I'm using a Digital Yachts transponder via a splitter on a VHF antenna that is sited about 250mm from the led bulb. Other yachtsman have told me that my AIS transmissions are OK but its getting very irritating to turn off my tri-light every hour to see if other vessels are in range. I've now noticed my LED masthead anchor light is having the same effect.

I guess this might be a common problem but can anybody suggest a simple solution other than changing back to a conventional filament bulb or moving the antenna?

Apologies if this subject has already been done to death but I'm out in the Cape Verdes and megabytes are too expensive to permit much research!


put a seperate aerial on the stern rail. mine picks up targets much further than i need & i have reduced the target list to 10 Nms

Salty John
27-03-14, 15:50
The problem is the power supply not the LED itself, although knowing this doesn't help you much. The buck-boost regulator in the light circuit controls the power supply to the LED and, depending on the type and the frequency at which it switches, can cause interference at vhf. You may find that you have problems with your vhf radio also if it shares the antenna located near the light.
Various fixes have been proposed - Orcagreen had a problem with this and they suggested using graphite beads fitted into the wiring to the lamp - I don't know if this would be the solution in your specific case.
Strangely, cheaper LED lamps that don't use Buck regulators don't have this same problem, and not all Buck regulators do - depends on the frequency at which they switch. Sorry I can't offer a solution. Others will be along to offer most positive solutions, I hope.

Martin_J
27-03-14, 16:18
I can see this question coming up many more times this season.

The new ISAF Cat 2 requirements for offshore racing for 2014 state that the AIS antenna must be at the masthead. Bearing in mind that many races also require the transmission of AIS with a Class B transponder, I can only guess that in most cases a splitter will be required in order to share the masthead VHF antenna.

For this reason I am currently looking around at splitters and having to bear in mind that a number of LED light fittings do emit at frequencies that appear to interfere (and due to differing technologies in use in the splitters, some may suppress LED interference better). I have a LED tricolour and anchor light at the masthead already.

What make of splitter do you use? I currently have Vespermarine, Raymarine, Digital Yacht, Em-Trak, Comar, AMEC, Sevenstar, Easyplit and True Heading in my shortlist...

Martin_J
27-03-14, 19:13
Hmm.. Been thinking a bit more about this and as Salty John says, if it is radiated interference (as it most likely is) from the power supply within the LED unit then any interference received by the antenna is not going to get filtered out by any splitter.

In fact the splitter should be passing everything through.. So perhaps the part of the LED unit with the high frequency power signals could be shielded better. Sounds like a task for the LED unit manufacturer.

My NASA Supernova combined tricolour/anchor light does not appear to affect radio reception although I think a bit more testing is now in order.

I will see what I can find in the way of interference at the weekend. None noticed so far but then I was not really looking for it.

Ashman
27-03-14, 19:47
Many thanks everybody for the responses, I'm going up the mast tomorrow to replace the bulb back to filament. We are crossing to Brazil in a week or so's time and probably will run the majority of nights without a tricolour to save power - risky I know but we'll keep a good watch and for most of the time there will be little shipping to concern us.
The splitter by the way is from Digital Yacht as well as the transponder.

Scotty_Tradewind
27-03-14, 19:51
I know little on this subject but would it help to move the aerial away from the LED on an extension bar of some sort or is this 'interference' transmitted over a long distance. ?
Why not have a separate dedicated AIS aerial away from the masthead?

best of luck,
S.

sailorman
27-03-14, 19:58
I know little on this subject but would it help to move the aerial away from the LED on an extension bar of some sort or is this 'interference' transmitted over a long distance. ?
Why not have a separate dedicated AIS aerial away from the masthead?

best of luck,
S.
mine on the stern rail has picked up vessels @ 70 Nmls, exceptional i know guess high pressure @ the time

JeffRobbins
27-03-14, 22:29
We've talked with several customers that have experienced RFI caused by LED masthead lights. The problem is switching noise within the marine band which is above the limits in the marine standards for this. A splitter likely won't help since the noise is within the band and so the splitter wouldn't be filtering it out.

The symptoms are often a high background noise level alert from the AIS unit (this alert is required by the latest Class B standard) and/or reduced target reception due to the noise level. We posted a technical note about it at http://tinyurl.com/mwx5kcy and you can find more info from Orca at http://ogmtechnical.blogspot.co.nz/2009/06/update-on-rf-interference-for-trianchor.html

If you've got one of our transponders, you can do a quick check.... on the AIS Status page it displays the RSSI on each channel. It's normal for it to fluctuate up and down. But if you switch your LED lights on and see the RSSI jump up and stay up, then you've got a noise source.

Martin_J
27-03-14, 23:01
My Advansea AIS transmitter also reports RSSI figures. I will disconnect it from the pushpit antenna at the weekend and connect it to the masthead antenna and see what difference is noted.
I will then reconnect the vhf radio and see if any audible noise received also changes (whilst listening to the AIS channels on the vhf) when the LED tricolour is switched on.

Martin_J
28-03-14, 02:10
Just back on board. With the VHF (using the masthead antenna) I tuned it to listen on channel 87 and 88 in turn... AIS clicks hard clearly on each channel and no discernable noise difference heard when either the LED tricolour or the anchor light switched on..
Not a perfect test. We shall test in more depth at the weekend but it looks like the Nasa Supernova is relatively noise free.

GHA
28-03-14, 08:20
Many thanks everybody for the responses, I'm going up the mast tomorrow to replace the bulb back to filament. We are crossing to Brazil in a week or so's time and probably will run the majority of nights without a tricolour to save power - risky I know but we'll keep a good watch and for most of the time there will be little shipping to concern us.
The splitter by the way is from Digital Yacht as well as the transponder.
Sounds like the best plan given the circumstances. And not really risky, there's next to nothing out there and anything you do come across will pick you up from ais or radar long before or even if visually . Anyway, you'll see them before they appear over the horizon.

Where in a Brazil are you looking to landfall? Jacare would get my vote.
Here's some pushpins might come in handy if you end up in Natal or Jacare.
https://maps.google.com/maps?hl=en&gl=gb&ui=maps

Enjoy :cool:

Ashman
28-03-14, 11:27
Sounds like the best plan given the circumstances. And not really risky, there's next to nothing out there and anything you do come across will pick you up from ais or radar long before or even if visually . Anyway, you'll see them before they appear over the horizon.

Where in a Brazil are you looking to landfall? Jacare would get my vote.
Here's some pushpins might come in handy if you end up in Natal or Jacare.
https://maps.google.com/maps?hl=en&gl=gb&ui=maps

Enjoy :cool:

Thanks GHA
Salvador / Baia de Todos os Santos is the target but it will depend on the trade winds once we've crossed the equator.......I don't want to go closer than a beam reach for comfort!

estarzinger
28-03-14, 14:25
By the way, the Optolamp (http://www.neptunes-gear.com/products/led-tri-color-masthead-light) has a different design power supply and produces no RF noise and no AIS interference. It's my 4th tricolor, as the first three (All major brands) all cut the AIS signal. The Opto is a very nice unit - they do have a couple models at different price points with fewer or more features (this link is to the fuller feature model).

Martin_J
28-03-14, 15:22
Out of interest..

What makes were the three (model and year) that did cause the interference?

When the lights were on, did you just not then have any AIS Rx or did your AIS receiver have an RSSI level indicator as indication?

Did these previous LED lights also cut your AIS transmission?

estarzinger
28-03-14, 16:47
^^ I started with two LED replacement bulbs (one was a BAY 15D TRI-COLOUR MASTHEAD, can't remember what the other model was), tried Lopo and then aqual signal.

Generally, with all of them, my ais reception range was cut by 50%. I know my ais transmission range was cut (i tried flipping the led on and off one night passage when I had another boat on the radio) but don't know by exactly how much.

I am told that Lopo has redesigned and theri RF noise is now better, but the bigger problem with them is that their reliability sucks. I still use them for my deck nav lights and even with the newest models I am only getting about a year between failures. They are terrific about replacing them for free, but it is a pain when cruising.

caerolusmagnus
28-03-14, 17:14
My arrangements are separate. Aqua-signal LED masthead tricolor, VHF Metz antenna on port side of masthead, about 15 inches out on a bar, same style bar on starboard side NASA AIS receiver again about 15 inches out on separate Metz antenna. Plotter is separate and below on internal antenna. Have not seen any adverse effects when switching the tricolor on and off.

NASA suggested there could be interference on AIS reception when VHF is on transmit but not too likely with the separation achieved. Still it would not be critical if such occurred. Also have VHF handheld and backup VHF with pushpit Metz antenna.

(All Metz from Salty John)

Paul_DY
03-04-14, 12:16
Hi Ashman, this is Paul from Digital Yacht and I have just read this interesting thread. I must admit that we have not had any direct contact from other customers about interference with LED Nav Lights, so I hope that it is not too common an occurrence. That said, I wanted to jump on this straight away and see if there was anything that can be done to fix the problem.

I have called Boat Lamps and spoke to Adrian the owner, who is also very interested in investigating and solving this problem. We have planned for him to send me a lamp with voltage regulator and then I will test it with our receivers and transponders. The goal is to try and recreate the problem and see if a fix can be found.

I am hoping to have my investigation sorted in 1-2 wks and I will post my findings on here as soon as complete.

Salty John
03-04-14, 12:30
It would be good if someone investigated this phenomenon - I thought it might be a good subject for a PBO/YM investigation to identify those LEDs that did interfere and those that didn't.

My own investigation leads me to the view that certain buck regulators with high switching speed, to reduce size and cost, are noisy and effect VHF reception and transmission.

This link takes you to a discussion on noise from a particular type of buck regulator:http://ww1.microchip.com/downloads/en/AppNotes/01466B.pdf

Manufacturers of masthead lights are aware of this problem and are, presumably, modifying their designs to use less intrusive regulators. Some don't use buck regulators for this reason, I think NASA might be one of those.

Martin_J
03-04-14, 23:18
My latest update is that I have now installed a splitter near the chart table so the VHF and the AIS Class B transceiver share the same masthead antenna.

I don't appear to have any interference when the NASA masthead lights are used. AIS RSSI levels are unaltered and AIS TX and RX looks to be unaffected.

As others have said.. it is looking like certain LED power regulation circuits cause issues.. but if they are interfering at the AIS frequencies then they could just as easily be interfering at close to (or on) your channel 16 frequency.. Definitely worth further testing.

chrisclin
20-04-14, 20:01
I am hoping to have my investigation sorted in 1-2 wks and I will post my findings on here as soon as complete.
Hi Paul,
are you anywhere near completing your investigations? I am waiting with bated breath as I am hoping to fit masthead LED lights before my mast goes up next week.

BERT T
20-04-14, 20:48
Notable silence from Adrian Jones???

nimbusgb
21-04-14, 05:59
Hi Ashman, this is Paul from Digital Yacht and I have just read this interesting thread. I must admit that we have not had any direct contact from other customers about interference with LED Nav Lights, so I hope that it is not too common an occurrence. That said, I wanted to jump on this straight away and see if there was anything that can be done to fix the problem.

I have called Boat Lamps and spoke to Adrian the owner, who is also very interested in investigating and solving this problem. We have planned for him to send me a lamp with voltage regulator and then I will test it with our receivers and transponders. The goal is to try and recreate the problem and see if a fix can be found.

I am hoping to have my investigation sorted in 1-2 wks and I will post my findings on here as soon as complete.

The right way to do this is with an RF frequency spectrum analyser. An expensive piece of kit unfortunately.

ianj99
21-04-14, 08:48
Its ridiculous not to mention potentially dangerous having to switch off lights to get an AIS signal or having to fit another antenna.

Surely the CE regs prohibit the sale of led lights that cause rf interference whether directly or indirectly (by allowing it to get in to the supply wiring)?

i would ask Ofcom for their opinion?

GHA
21-04-14, 09:11
The right way to do this is with an RF frequency spectrum analyser. An expensive piece of kit unfortunately.
Would an oscilloscope be of any use?

With a USB scopeI I can just see a blip which seems to coincide with a target coming in but see no change turning on and off the lopo light.

lw395
21-04-14, 09:27
Its ridiculous not to mention potentially dangerous having to switch off lights to get an AIS signal or having to fit another antenna.

Surely the CE regs prohibit the sale of led lights that cause rf interference whether directly or indirectly (by allowing it to get in to the supply wiring)?

i would ask Ofcom for their opinion?

I suspect that the problem may be the long runs of cable parallel in the mast.
The switchers will be running at most a few MHz, AIS is over 160MHz, it's unlikely to be 160MHz RF coming from the LEDs.
I would not be surprised if the mechanism was actually switching pulses at a few MHz coupling into the aerial line from the light wiring.
Some filtering (of the light wires) at the masthead might well work.
A choke/inductor good for a few MHz and some small capacitors would be a starting point.
It can also help to have the light wiring twisted together.
Also, it might be worth making sure the AIS receiver has good rejection of low frequency blocking, maybe put a high pass filter in the aerial line to cut off everything below say 50MHz.
Unfortunately, if it's a transceiver, that filter will need to be rated for 25 Watts, hence expensive.
A ferrite ring around the coax might help, by stopping 'common mode' current flowing in the outer.
Also looking at the grounding of the AIS set relative to the lights. Big earth loops can be a nuisance.

I don't think OFCOM or CE will help, it's probably as much to do with installation practice as product design.

ffiill
21-04-14, 09:29
For what its worth my kitchen mains led spots(12) completely jam FM reception in my house!

lw395
21-04-14, 09:34
Would an oscilloscope be of any use?

With a USB scopeI I can just see a blip which seems to coincide with a target coming in but see no change turning on and off the lopo light.
Look on the light wiring.
A good scope might see switcher noise at 250kHz to a few MHz. There are scopes that work above VHF but ....
If you can see the low MHz noise and cut it down with filtering, you'd be very unlucky if you weren't cutting its harmonics too.
The signal that actually gets to the receiver only needs to be microvolts to block the channel. That's not easy to see.

ianj99
21-04-14, 09:38
Won't pass any CE conformity tests* and are they affecting your neighbours radio reception? If you had the spots onboard, would they jam your VHF?

*These basically state that electrical/electronic equipment must neither cause interference to other equipment nor be susceptible to it.

The problem is that CE is a self certification process so I suspect that many products are never actually tested: the manufacturers just stick on the CE label.

ianj99
21-04-14, 09:46
I suspect that the problem may be the long runs of cable parallel in the mast.
The switchers will be running at most a few MHz, AIS is over 160MHz, it's unlikely to be 160MHz RF coming from the LEDs.
I would not be surprised if the mechanism was actually switching pulses at a few MHz coupling into the aerial line from the light wiring.
Some filtering (of the light wires) at the masthead might well work.
A choke/inductor good for a few MHz and some small capacitors would be a starting point.
It can also help to have the light wiring twisted together.
Also, it might be worth making sure the AIS receiver has good rejection of low frequency blocking, maybe put a high pass filter in the aerial line to cut off everything below say 50MHz.
Unfortunately, if it's a transceiver, that filter will need to be rated for 25 Watts, hence expensive.
A ferrite ring around the coax might help, by stopping 'common mode' current flowing in the outer.
Also looking at the grounding of the AIS set relative to the lights. Big earth loops can be a nuisance.

I don't think OFCOM or CE will help, it's probably as much to do with installation practice as product design.

The point is: the light should NOT be allowing any interference to get back into the wiring. Its not acceptable that you should have to poke about with a scope or spectrum analyser or start adding ferrite rings to existing wiring whether DC or RF or even to the existing wiring to the light.
If you had paid a marine electrical engineer to install the light and then had AIS problems, you'd not be impressed if you were told you then had to pay extra to cure the interference from said light or even worse, switch it off when you wanted to check for AIS targets.

You should fit a properly CE certified light and get a refund on the original.

I'm sure Ofcom would certainly be interested if anyone was selling any product that interfered with reception in the marine VHF band and would recommend you remove it immediately.
I

Salty John
21-04-14, 09:53
Interference from buck regulators (even at 150 MHz) is well documented - see my link above for one of many examples. The responsible manufacturers of these regulators warn about this problem and advise methods to control it and also advise where a particular product is not suitable because of the probability of radio interference.

The problem is mis-application of particular types of buck regulator when they have to operate close to vhf equipment. I suspect all the main LED nav light suppliers are aware of this problem, but those that make LEDs for general use may not have planned for this issue.

If you put LED nav lights in close proximity to vhf antennae, check for interference. Simple.

Salty John
21-04-14, 09:56
Perhaps PBO or YM would do some independent, unbiased, research into this issue?

ianj99
21-04-14, 10:31
Perhaps PBO or YM would do some independent, unbiased, research into this issue?

Sounds like they should since its not imho a minor issue and indicates poor design and inadequate CE testing.

lw395
21-04-14, 10:32
The point is: the light should NOT be allowing any interference to get back into the wiring. Its not acceptable that you should have to poke about with a scope or spectrum analyser or start adding ferrite rings to existing wiring whether DC or RF or even to the existing wiring to the light.
If you had paid a marine electrical engineer to install the light and then had AIS problems, you'd not be impressed if you were told you then had to pay extra to cure the interference from said light or even worse, switch it off when you wanted to check for AIS targets.

You should fit a properly CE certified light and get a refund on the original.

I'm sure Ofcom would certainly be interested if anyone was selling any product that interfered with reception in the marine VHF band and would recommend you remove it immediately.
I
I agree with your sentiment, but the allowed emissions are not zero.
Radio receivers are by their nature sensitive.
Couple the two too closely and the blame is split.
EMC (electromagnetic compatibility)radiated testing tends to be done at a range of a few metres, not a few millimetres as might be the case inside a mast.
Also, I've seen plenty of instances of things like switching power suppliers working quite cleanly when powered directly from a good 12V supply, but very dirty when on long leads.

Unfortunately, just because a bunch of products like a light and a radio pass CE individually does not mean they will be OK together, particularly if the installation is done in an 'RF unaware' way.

I do have access to spectrum analysers and so forth, it might be interesting to measure emissions from some of these lamps.
Also maybe the front end of the AIS receiver might be more susceptible to out of band than is desireable.
It's a long way from proven that the light is emitting directly on the AIS channel.

Unfortunately, most of this stuff is designed down to a price, and sticking in a quid's worth of extra components to improve EMC in 'real life' installations falls by the wayside.

ianj99
21-04-14, 10:39
I agree with your sentiment, but the allowed emissions are not zero.
Radio receivers are by their nature sensitive.
Couple the two too closely and the blame is split.
EMC (electromagnetic compatibility)radiated testing tends to be done at a range of a few metres, not a few millimetres as might be the case inside a mast.
Also, I've seen plenty of instances of things like switching power suppliers working quite cleanly when powered directly from a good 12V supply, but very dirty when on long leads.

Unfortunately, just because a bunch of products like a light and a radio pass CE individually does not mean they will be OK together, particularly if the installation is done in an 'RF unaware' way.

I do have access to spectrum analysers and so forth, it might be interesting to measure emissions from some of these lamps.
Also maybe the front end of the AIS receiver might be more susceptible to out of band than is desireable.
It's a long way from proven that the light is emitting directly on the AIS channel.

Unfortunately, most of this stuff is designed down to a price, and sticking in a quid's worth of extra components to improve EMC in 'real life' installations falls by the wayside.

I agree that the CE regs also imposed a duty on manufacturers to make their equipment as immune from interference as possible as well as not causing it.
Until some independent tests are carried out we'll never know what's going on.

lw395
21-04-14, 10:40
Sounds like they should since its not imho a minor issue and indicates poor design and inadequate CE testing.

Perhaps some of the 'poor design' blame needs to be pointed at those deciding that all this stuff needs to be co-located at the masthead, and at the yacht level rather than the sub-system level?
It all seems very similar to a project I worked on, lots of stuff that worked fine in itself, not so good when installed on the same vehicle....

The danger is you will need a ce approved or whatever bloke to wire your mast.

GHA
21-04-14, 11:47
Some scope images....
With a bedazzled LED and lopolight tricolour

Worth noting I can tell no difference in ais reception with lopo being on or off, though there are reports of people who have.
Also using a SSB reciever the bedazzled LED's are noticable with the antenna a almost touching the LED but silent further away. Unlike a previous fluorescent tube which was extremely RF noisy. The fridge is noisy in the ham bands, haven't tried it further up, think it's OK.

So this all tells us........ almost nothing :)
..
Sharing feed with a usb charger and LED not connected..
http://i204.photobucket.com/albums/bb10/yacht_conachair/sharednoled-1_zps45ffa300.jpg..

Shared USB with LED
http://i204.photobucket.com/albums/bb10/yacht_conachair/sharedwithled-1_zps697a9464.jpg
Almost direct to battery with no LED
http://i204.photobucket.com/albums/bb10/yacht_conachair/directnoled-1_zpsc6a2c7e7.jpg
Almost direct to battery with LED
http://i204.photobucket.com/albums/bb10/yacht_conachair/dierctwithled-1_zpsb2ec3ca9.jpg
To Lopo inside swith turned off
http://i204.photobucket.com/albums/bb10/yacht_conachair/tricolouroff-1_zpsd9422cf4.jpg
To lopo turned on
http://i204.photobucket.com/albums/bb10/yacht_conachair/tricolouron-1_zpsb2bc7270.jpg

lw395
21-04-14, 12:59
Some scope images....
With a bedazzled LED and lopolight tricolour

Worth noting I can tell no difference in ais reception with lopo being on or off, though there are reports of people who have.
Also using a SSB reciever the bedazzled LED's are noticable with the antenna a almost touching the LED but silent further away. Unlike a previous fluorescent tube which was extremely RF noisy. The fridge is noisy in the ham bands, haven't tried it further up, think it's OK.

So this all tells us........ almost nothing :)
..


Well it tells me that the lopolight is not nearly as bad as the usb charger.
You can see why things like phone chargers often ruin Navtex reception, which is around 500kHz.
In my view, I would hope a VHF/AIS receiver would be fairly well immune to noise under a MHz, otherwise it might have a hard time on a boat with an HF or MF transmitter.
Alternators, solar panel regulators and so forth will also create noise, and with a lot more power behind it.

The traces also suggest that the 12V system is quite high impedance at a few 100kHz, a lower impedance might turn those voltage spikes into current spikes, the trick is to absorb some of the energy in the process...

Thanks for posting useful pictures!

Paul_DY
14-05-14, 00:11
Hi this is Paul from Digital Yacht again. Sorry for the time it took me to complete the investigation but this is a really busy time for us and I have only been able to work on this in the evenings.

I have now completed my testing of a number of different LED lights/bulbs from various manufacturers and in my tests a small number of LED Navigation Light systems were found to potentially cause interference with AIS reception, if the cable to the light was run directly alongside the VHF antenna cable.

The electrical noise was generated by the switch mode regulator in the LED Navigation Light and we would recommend to all manufacturers of these lights to look closely at using lower frequency switch mode regulators and fitting suppression filters.

The noise was pre-dominantly radiated (through the air between the cables), rather than conducted (through the wiring) and routing the LED Navigation Light cable away from the VHF Antenna cable had the biggest positive affect on reception.

Differences were found between manufacturers and even between different LED Light models in the same manufacturer's range, so we would recommend checking an LED light before fitting them on a boat with an AIS system installed. This can be done by placing a coil of LED Light power cable alongside the AIS VHF antenna cable and checking if the RSSI figure increases or checking the number of AIS targets with the LED Light ON and then when you turn the LED Light OFF.

Below is an oscilloscope image of the noise created by one light that caused total loss of AIS reception and was the worst of the lights tested. You will note that the actual voltage of the noise is not great (<100mV) but it is the frequency of the signal and the sharpness of the leading spike that causes the problem. In fact we found lights that created larger amounts of noise (in terms of voltage) but the frequency and smoother waveform resulted in no affect on the AIS reception.

42546

William_H
14-05-14, 01:21
It did occur to me that it may be possible to vary or even fix the interference without going up to the nav light. If a variable resistor or variable voltage linear regulator were connected in the power supply to the LED then at lower supply voltages some buck regulators will increse the mark space (on off ) ratio to the point where they are on almost all the time. This should vary the interference or possibly stop it or move it's frequency out of band.
So something like an LM 317 regulator with a potentiometer on the output such that you can vary the voltage supplied to the LED. Reduce the voltage supply to the point where the LED loses brightness. Check for interference. Check for interference at various supply voltages to the LED. The different voltages may cause the LED oscilator to run at different frequencies so different degrees of interference. Depending on the current drain of the LED and the voltage you reduce to, it may overheat the LM 317 so you may need an LM317K metal IC with a heat sink. Check the specs for the regulator and the LED. good luck olewill
This would be a very crude fix but having the advantage that you can do it from below. good lcuk olewill

chrisclin
24-05-14, 12:11
Thanks for your reply, Paul. Too late for me - the mast went up with old technology bulbs on it, but there does seem to be a solution for next time the mast comes down. Presumably you aren't willing to publish recommendations on a public forum but it will be worth contacting you when the time comes. Apart from anything else, the speed of change in the LED world is such that any recommendations become out of date very quickly.