A novice builders experience with building a Jabiru J430 aeroplane.
Radio Noise Issues
I have been plagued by various noise issues from the time I started flying the aircraft. Most times it has been just a minor irritation but I have had several times where it got worse and have actually been refused permission by air traffic control to take off on two occasions because of noise in radio transmissions that was so bad they could not understand me. I am now (after about two years) getting to the stage where I have it usable though by no means perfect.
The basic problem:
In a nutshell the problem is the Microair radios AND the Jabiru ignition system. The radio design is susceptible to Radio Frequency Noise and the Jabiru Ignition System is a very noisy system.
It is highly unlikely you will be able to get a perfect result while you have both in your aircraft.
About 90 % of my problems have been on the receive side. In fact I used to be regularly told the transmit signal was very clear, although that changed for a while.
What causes the problems?
The Microair radios
Basically the Microair radios have poor noise rejection capabilities. Even putting filters on almost every wire in the aircraft really only resulted in some decrease, not elimination, of the noise.
They seem to pick up extraneous Radio Frequency (RF) noise from any source. We have had Microairs (in a mate's Glassair) that were pretty bad with ignition noise which were replaced with another brand (Becker) and instantly cured the problem.
The problem I have is compounded because I have two radios and an intercom. The RF can be picked up by any of the wire looms external to the radios and carried into the radio.
Jabiru now actually recommend either Becker or even better Funkwerk radios over Microair, for the noise issues. The advantage of the Funkwerk (Funkwerk ATR833 VHF Transceiver)
is that they now make a single box that has two listening frequencies and a 4 place intercom combined which will remove all the external looms that can act as an antenna for RF. (The trade off though is that if one goes U/S they all go)
The second part of the radio equation is the coaxial cable. My kit came with cheap coaxial cable. This should be thrown out immediately and replaced with RG400 aviation standard cable.
The cheap stuff has single layer outer shielding which is quite thin. I was able to increase and decrease my ignition noise by bending the cable under the dash. There is absolutely no doubt that it lets lots of RF through the shielding especially if you have to bend it. RG400 is proper aviation grade cable. Also it is important to use top quality plugs. All the books I read state you should use crimp types in preference to solder types and to not even consider using the screw on type ones (the ones provided in the kit.)
So in summary, buy better radios, better cable and better plugs. Easy!
The Jabiru Ignition Noise
Unfortunately the simplicity and cheapness of the ignition coil system comes at a cost. They are a VERY noisy system. I have done a huge amount of research on these issues and have found some interesting information.
Firstly Jabiru themselves have put a lot of time and money in and have not found a cure for the problem. Rod Stiff told me himself they have tried everything and can't completely remove the noise. The chapters in the construction manual allude to the difficulty but the fixes they suggest only go some way to helping but they don't expect them to cure the problem.
Without going to some other system we are stuck with the noisy coils. So the next best thing to do is to work at the wiring installation and shielding. I would commend the chapter in the Jabiru manual but would also add that you should undertake some preliminary reading about electronics and wiring.
I also found others that were useful for a few bits but often not much beyond that. I also spoke to several radio techs, including one tech who claimed to be very experienced on Jabirus. However they all were able to only give general advice as every aircraft has slightly (or very ) different wiring, connections, components etc and what work's on one aircraft may not work on others.
So some general ideas to try.
You have to ensure all your connections are secure and earths good.
Minimise the lengths of your wiring and don't have redundant loops.
Don't have wires that carry any hint of AC type, RF or potential signal tied in
bundles with any of your radio, intercom or headset wires.
Buy yourself a large number of ferrite beads ( circular or clamshell types)
and preferentially install them with a loop going through the ferrite twice.
(I have not worked out if any particular wires really have more effect than others.
I put them on everything I could!)
Things that didn't work for me included:
Shielding the spark plug leads or distributor and coil leads - well it actually worked
but made the engine unreliable.
Randomly replacing leads, components and coils & changing gaps made no difference
at all and was an expensive waste of time.
I also learned to be very wary of professionals who tell you “I do this and it works EVERY time!” I have spoken to some of their customers who had a very different opinion of their success rate!
Something I found in an article somewhere (which I have now lost) and which I found in my aircraft is that it is likely that you will never find a single magic bullet that cures all. It is likely that those things that do help will help a little and the cumulative effect will be a cure or at least a decrease in the noise to an acceptable limit.
So without labouring the points I will list what problems I had and what helped. Try them all and see what works. Something that didn't work on mine may work on yours. Click to download the spread sheet
Something I did find is that ferrite beads, which are basically the “cure all” in the Jabiru manual, don't work just “anywhere” on the wires. They don't work much but when they do I found I had to slide the ferrite back and forth along the wire near the connector till I found the “sweet spot”. In most cases it is a few inches from the end, not right at the end itself. In some cases it made no difference at all but it seemed to be a case of if it was going to work at all you had to actually have the engine running and the radios on to find the best spot. That proved quite tricky at times.
Overall, what I have found is that if you want to work within the parameters of the Jabiru ignition system and Microair radios you have to be prepared for lots of trial and error. Don't expect a single cure but rather a cumulative gradual decrease in noise. But the most daunting problem I have found is the changing nature of the causes. I have had things seemingly work when I have tried them and then have the noises return later.