Light Aircraft Association

Hi folks

I wondered if anyone else has experienced similar RF problems to me with a leburg system. I am having no problems with tx on my ICOM A6 installation but noise induced crackle for all receive frequencies. I have tuned the antenna and ground plane with a SWR meter. I know the antenna and radio and power supply are fine when the engine is off and have confirmed it is RF because any handheld radio within about 50 metres of my airplane picks up the interference. Basically the ignition set up is a big RF transmitter! I have no other problems with powered devices, I have an inline power filter. My guess is that the noise is coming from the ignition system components. The coils are ex honda CBR coils and the rest is made up of the usual leburg ignition units. I have shielded the silicon ignition HT cables with braid and earthed them.

I have read about 2 stroke engine rf problems with electonic ignition but not heard anyone with leburg 4 stroke.

I did not build the plane or install the ignition but have a good idea about what is what.

If anyone has any ideas or similar experiences I would greatly appreciate them?

Thanks

Tony Barber
Colibri G-BNDP

Hi Tony,

Have you always had the interference problem or has it just started happening? Also, is interference present on both left and right systems? I don't have any specific knowledge of Leburg systems, but RF is RF!
Regards

Tony Nowak

Copied from the new Leburg website ...

"Re HT leads for Ford coils on the Leburg system.

I have always supplied Lemark Hotwire leads (PE24 and PE36) with no problems reported. These have the added benefit the the plug connectors can be bent to have a straight or angled entry.
If you have the heavier coil with turrets you will need the X-kit also.

Halfords and Partco have supplied them, otherwise try Martins Motor Supplies Swindon.

I suggest that you stick to the distributed resistance type of HT leads, which are probably best at damping down the "ringing" that is the main source of the RF interference.

Also, we had persistent problems from one user, who had supplied his own leads with low resistance cores. When I supplied the usual set, all problems of blowing up output transistors dissappeared.

Also, I avoid the type with coiled conductors. I don't see how having extra inductance in the plug leads has any benefit, and I suspect that these increase the stress on the driving transistors. The transistors I use have overvoltage protection built in, but I would prefer to avoid the source of the stress rather than rely on the protection.

The Leburg system worked well from the start, and the controllers have changed very little. However users are full of bright ideas, some of which are good, some bad. Much as I wanted to avoid damping down the ideas of others, I found that I had to become more prescriptive in defining the installation.

The installation recommendations are as much a process of evolution as engineering, in that where an individual recommendation is made, at least one snag was solved, although I might only be able to explain vaguely why, in engineering terms. As the system now seems reliable, that process has worked, so we have probably combed out the snags.

I suggest that each user takes advantage of learning from earlier mistakes and follow the recommendations, otherwise he risks stepping into an area where a snag lurks.

Re radio noise.

The first step is to fit a halfway decent aerial as far from the engine as possible. If you have a rubber duck stuck on the top of a handheld clipped to the instrument panel, then you can expect a noisy and ineffective radio.

Re the Leburg system, there are two sources for "radio" noise.

One is due to radiation from the ignition system. The distributed high resistance leads are very effective at reducing the radiated noise, and grounding the engine, engine mount, firewall, instrument panel etc helps.

The second source is alternator noise in the form of spikes on the +12V supply from the rectifier/regulator, which is cheap (which users like), effective, but crude. A cheap 12V, LDO, 3 terminal regulator on a bit of Vero board will get get rid of these spikes.

David Mickleburgh"

Hope something in there may help? I had no problems when I fitted a Leburg to my old T31m having followed the instuctions to the letter.

Ivan
________
Michigan Medical Marijuana

Hi Ivan

yes thanks I have seen this already. I have also has a long conversation with Dave Mickleburgh before he passed on about it. Basically Dave said its the antenna and or the electrical noise from the alternator and to fit a decent antenna and add a LDVR. Both of which I have and make no difference. The noise is generated by both left and right ignition modules although is abates slightly with one or the other switches off. The aircraft has always had this problem and the previous user reported it also. My first thought was to try metal cased spark plug caps but I am more inclined to think this is coming from the ignition modules or cables or some bad ground somewhere. Although a bad ground would manifest itself by a component not working I would have thought?

Yours very frustratedly

Tony

ivanmanley wrote:Copied from the new Leburg website ...

"Re HT leads for Ford coils on the Leburg system.

I have always supplied Lemark Hotwire leads (PE24 and PE36) with no problems reported. These have the added benefit the the plug connectors can be bent to have a straight or angled entry.
If you have the heavier coil with turrets you will need the X-kit also.

Halfords and Partco have supplied them, otherwise try Martins Motor Supplies Swindon.

I suggest that you stick to the distributed resistance type of HT leads, which are probably best at damping down the "ringing" that is the main source of the RF interference.

Also, we had persistent problems from one user, who had supplied his own leads with low resistance cores. When I supplied the usual set, all problems of blowing up output transistors dissappeared.

Also, I avoid the type with coiled conductors. I don't see how having extra inductance in the plug leads has any benefit, and I suspect that these increase the stress on the driving transistors. The transistors I use have overvoltage protection built in, but I would prefer to avoid the source of the stress rather than rely on the protection.

The Leburg system worked well from the start, and the controllers have changed very little. However users are full of bright ideas, some of which are good, some bad. Much as I wanted to avoid damping down the ideas of others, I found that I had to become more prescriptive in defining the installation.

The installation recommendations are as much a process of evolution as engineering, in that where an individual recommendation is made, at least one snag was solved, although I might only be able to explain vaguely why, in engineering terms. As the system now seems reliable, that process has worked, so we have probably combed out the snags.

I suggest that each user takes advantage of learning from earlier mistakes and follow the recommendations, otherwise he risks stepping into an area where a snag lurks.

Re radio noise.

The first step is to fit a halfway decent aerial as far from the engine as possible. If you have a rubber duck stuck on the top of a handheld clipped to the instrument panel, then you can expect a noisy and ineffective radio.

Re the Leburg system, there are two sources for "radio" noise.

One is due to radiation from the ignition system. The distributed high resistance leads are very effective at reducing the radiated noise, and grounding the engine, engine mount, firewall, instrument panel etc helps.

The second source is alternator noise in the form of spikes on the +12V supply from the rectifier/regulator, which is cheap (which users like), effective, but crude. A cheap 12V, LDO, 3 terminal regulator on a bit of Vero board will get get rid of these spikes.

David Mickleburgh"

Hope something in there may help? I had no problems when I fitted a Leburg to my old T31m having followed the instuctions to the letter.

Ivan

Tony,

I notice in your first post that you have shielded the ignition leads and earhed the shielding. I had a similar problem of radio interference on my biplane when it was fitted with a VW. That installation had Slick magnetos, but the interferance was from the leads. When I fitted braded shielding the problem went away, but at that time I was advised that the shields must only be earthed at one end, and that is how I fitted them.

Kind Regards

Barry Plumb

Hi Barry

I have earthed the leads in a rather more haphazard way in effect they are grounded somewhere in the middle and by a combination of being interconnected. Which end did you ground them at ?

Regards

Tony

Barry Plumb wrote:Tony,

I notice in your first post that you have shielded the ignition leads and earhed the shielding. I had a similar problem of radio interference on my biplane when it was fitted with a VW. That installation had Slick magnetos, but the interferance was from the leads. When I fitted braded shielding the problem went away, but at that time I was advised that the shields must only be earthed at one end, and that is how I fitted them.

Kind Regards

Barry Plumb

Hello Tony,sorry for butting in on your problem but we have exactly your symtoms on our jabiru hawk. what caught my eye was ivan's reply regarding ign' harnesses , we have a harness cut to size with the leads to no 3and 4 pots shorter than 1@ 2. should they all be the same length and equal resistance? and how much supression +resistive plugs can be used before the spark disappears .cheers jb.

Hi Jim

Do you have a Leburg EI system? I can pass on on data that Dave Mickleburgh had given to me if so and it will be relevant. There is a lot of info on this topic all over the Internet, its not totally uncommon but it does manifest in different ways it seems. I am still a rookie but have learnt a lot.

If you have resistive leads such as the silicon core ones then ideally they should all be the same length so that the spark intensity is the same on all cylinders. If you have resistive caps or plugs then with copper cores then length is not an issue. With the leburg system Dave recommended at least 5kOhm between coil and plug and 5-10kOhm is considered optimum. Mine are silicone core cut to length for about 7kOhm. I had them made by www.fastlaneauto.co.uk.

I have shielded them with tinned copper braid and 'loosely' inter-connected them via an earth wire (standard copper earth wire as used in domestic appliances). However, after reading Barry Plumb's post I have got some flat tinned copper earth braid and individually earthed all of the HT leads with it at the plug end. I have only done the bottom plugs so far but results suggest that in the 'bottom' ignition module the noise has radically reduced. This weekend I intend to do the top plugs and fly so that I can test at full throttle.

Speaking to others who know far more, it seems that where earth is concerned the surface area is more important than the volume when considering current and RF effects. So replacing the earth connections with flat braid and earthing only at one end seems to be the way forward. I should be able to confirm next week.

I am happy to pass on my hard fought experience if you want to know more. Just drop me a PM and I will send my phone number.

Regards

Tony

jim bolton wrote:Hello Tony,sorry for butting in on your problem but we have exactly your symtoms on our jabiru hawk. what caught my eye was ivan's reply regarding ign' harnesses , we have a harness cut to size with the leads to no 3and 4 pots shorter than 1@ 2. should they all be the same length and equal resistance? and how much supression +resistive plugs can be used before the spark disappears .cheers jb.

I will add that in my opinion having slightly different length resistive leads is neither here nor there really and I would not think this is causing an RF problem. Its more likely to be earthing and shielding of some form.

jim bolton wrote:Hello Tony,sorry for butting in on your problem but we have exactly your symtoms on our jabiru hawk. what caught my eye was ivan's reply regarding ign' harnesses , we have a harness cut to size with the leads to no 3and 4 pots shorter than 1@ 2. should they all be the same length and equal resistance? and how much supression +resistive plugs can be used before the spark disappears .cheers jb.

I am not familiar with the Leburg system but..

does the system have wires to 'kill switches' or similar??

My Slick mag system was as quiet as a mouse but then started to increasingly crackle on the radio after a year or so.

The cause was eventually found at annual - the screw earthing the ring terminal on the wire connected to the shield braid of one of the kill switches had worked very slightly loose. It was only earthed at one end (magneto end) as per correct practice.

Half a turn with a screwdriver and all was restored to quietness.

Moral - don't underestimate what the earthed shields do - even low the voltage wires can cause interference.

Good luck Sherlock!

Hi folks

tried grounding the braid on all the 8 HT leads at the plug end. No joy.
tried grounding them other end (ignition module). No joy.

Tried shielding the plugs with braid, no joy.

In fact the noise now seems worse than ever before.

Only things left to try are proper shielded plug caps and a 22uMF capacitor in the power supply.

In response to Steve, the wires to the kill switches for the ignition modules are insulated copper core, i.e not shielded. But then no other system has shielding either on this installation. It was built in line with leburg recommendations to my knowledge but it was the second unit ever installed.

Without stripping out the engine and rewiring I am at a bit of a loss now. The radio is nigh on unusable but thanks for all your ideas.


Tony