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Jabiru 3300 rf Noise
Now that I'm over half-way through Phase I in my 750/Jab 3300, I'm starting to troubleshoot minor glitches. I've got a MGL V6 comm with a Comant antenna, and it works great - ATC, etc., reads me "loud and clear" and nearby transmitters and ATC are received equally well. However, if I get a weak or distant transmission, there is a strong "ignition" noise in the background - it defintely varies with engine rpm. The noise was equal on either mag. (The p leads are shielded and grounded to the engine and the ground on the mag switch.)
I researched this on the web to the nth degree. My engine is of relatively recent production and has resistor spark plug leads. I decided I might get some benefit from resistor plugs, so I went with the NGK DR9EIX - they're resistor, but the iridium means they'll fire at lower voltage, so the additional spark plug wire resistance shouldn't present a problem.
They worked ... sort of! The right mag became COMPLETELY quiet! However, the left sounded about the same! While checking the distributors for secure connections, etc., I noticed the right mag lead was labelled "High Temperature Suppressive", while the left was labelled "Electra Cable ECA 7". Now I'm wondering if the left lead is NOT rf suppressed (or maybe Electra Cable makes crummy cables)??? I had some ferrite beads and added four on the left lead - this made it quieter, but not completely quiet.
Does anyone know if the mag leads can be changed out with a quality rf suppressive lead such as one from Accel, etc? How are they attached to the mag? Can the existing lead be removed without damaging the mag?
I currently (pun intended!) have a #4 ground cable from the starter to the battery, but I "think" I only used a #10 from the battery to airframe. I think I'll upgrade the grounds with a braided strap between the battery and airframe and also add a braided strap between the engine and airframe to ensure good grounds and have some redundancy. I also read in the engine manual about grounding the carb to the engine - apparently it can generate rf noise? - guess I'll had a ground strap there, too.
Any insights or other ideas?
Replies to This Discussion
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Permalink Reply by Phill Barnes on
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Hi John
RG400 is supposed to be much more resistant to RF noise than RG58 but who really knows. That may be in a theoretical world. Either way, it certainly won't hurt to try the ferrites. I was provided with ferrite rings that are added and fastened with heatshrink to one end of the cable before the ends of the cable are swaged. I just looked through the Icom installation manual online and couldn't find reference to them. It is possible it was commant who supplied the ferrites, not sure now. Either way, it was the idea of an aviation communication company and not mine so there must be some merrit in it. Hope you get it sorted mate.
Phill
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Permalink Reply by Thomas Richardson on
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John, I have a friend that just went through the same issue and has it solved. If you will contact me privately, he is willing for me to give you his phone # to talk to about it.Turns out it was a Jaiburu issue that he found after many hours of re-work.
Tom Richardson
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Permalink Reply by John Austin on
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I called Tom's friend and this was really interesting! His Jab 3300 had an identical ignition noise. Ironically, it all centered on the left mag coil, like mine (although his engine is 4 years older than mine). An ohm meter check showed no continuity between the coil and the end of the HT lead. Incredibly, although his engine was running fine, it turned out the coil HT lead was not even making contact with the barbed terminal in the coil (which was bent, too)! It was carrying the current by arcing, thereby generating the rf noise. When he straightened the terminal and reseated the HT lead, the noise was gone.
I've largely got a pretty quiet radio now, but I'm definitely going to check the coil's resistance between the coil and the lead (5.9-7.1 kohm) at the 50 hrs check coming up soon - as I posted earlier, I've always been suspicious of that left HT lead.
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Well, darn! Checked the left coil and it was 7.1 kohms ... exactly to spec! Oh well, like I said, it's really pretty quiet with the ferrites on the HT lead. I originally only had some ferrites that were a little too big, so I wrapped the areas where they were applied with silicone tape to make a snug fit (I understand a snug fit is important for them to work properly.) I now have some 7mm ferrite clamps, so I'm going to install them while I'm down for the 50 hr checks.
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Hi John
I just re read you post regarding carb earthing. The carb has a earth wire preinstalled from the factory and it has a spade terminal on one end. Aparently if this terminal is not connected, the throttle cable acts as an RF antenna and must send the noise to the panel area. I learnt this from the Homebuilt Help DVD, Jab FWF installation. The other thing that I did that is not even done at the jabiru factory on their planes, is to use shielded wire for the headset jacks and the shielding gets grounded at one end only. I grounded at the radio end.
Phill
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Phill - I guess you missed last Tuesday's post - the joke was on me! After carefully earthing the carb, I happened to see the factory earth wire way up on the top of the carb! It had been there all along! I don't know how I missed seeing it! Well, she's got two carb earth wires, now! LOL!
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Hi John
No I didn't see your Tuseday post but no matter. What does matter is that you actually found the cause, you must be stoaked. I hope we will see videos soon.
Phill
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Long-term follow-up:
I've got the 750/Jabiru 3300 so dialed-in as far as day-to-day operational parameters - CHT's, EGT's, oil temps, etc., that I've returned to chasing down very minor nuisances just for the heck of it! I still have a bit of rf ignition noise with weak/distant transmission reception. I decided to have another go at it, and upon close inspection, found a curious thing: my engine (#2427), as delivered from Jabiru, has a "Jabiru" coil/lead on the left and a Jabiru-modified "Honda" coil/lead on the right. I had noted earlier that the leads were different, but never really closely examined the coils!
I checked with Jab USA as to whether this was correct and if there was some reason for the two different coils. The best explanation they could give me was that perhaps my engine just got caught in a changeover to the latest Honda coil, so I got one of each. Jab USA reassured me the coils are completely interchangeable, but all they stock now are the modified Honda coils (@$169 each!)
Comparing rf ignition noise on the left (Jabiru) vs right (Honda), it was still obvious the right/Honda coil and lead had much lower noise. I therefore determined to modify a Honda coil and install it on the left, replacing the Jabiru coil and lead. I obtained two (I wanted a spare) 30500-ZE2-023 Honda coils from Partspak.com for approximately $80 delivered. I obtained a 3' length of KV85 spiral wound core suppression wire from Magnecor (probably the best quality obtainable) with distributor connectors and boots on each end for $30 delivered. This can be cut in the center so as to have two coil leads.
The Honda coil has the original, stranded copper, non-suppressed lead epoxied into the coil tower. You have to basically use an Exacto knife and forceps to remove the wire from the tower, clean it up with a file, and then insert the new coil lead. Since the Magnecor is a spiral wound core with a non-conductive center, the most sure way to get a good connection is leave about 1/8" of the conductor exposed and bend it to one side. This will ensure the spike in the coil tower penetrates the conductive portion of the core. I reduced the 8.5 mm diam silicon rubber insulation to about 7mm, lubed it with epoxy, and inserted it into the coil tower. A heat shrink sleeve was used for further security.
I immediately checked the continuity and resistance of the coil and lead to assure I had a good connection before the epoxy set up! All was OK! Whew! I then changed out the modified coil for the noisy Jabiru coil and lead on the left and was rewarded with less rf ignition noise than the original Jabiru-modified Honda right coil and lead!
I've seen no difference in operational parameters such as rpms, etc. I plan to test it for about 10 hrs to assure it's a reliable coil and lead, then I think I'll modify my spare with the remaining Magnecor lead and change out the right coil, too.
John
N750A
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Permalink Reply by David W. Brown on
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I have always had bad ignition noise with my 750 hr jabiru 3300 601XLB. I had tried all the grounding and shielding techniques that have been suggested. I just learned to "live with it". Recently the left mag developed a greater RPM drop. Upon examination the resistance showed open in the high voltage lead to ground, right mag okay. So I ordered a new Honda mag and Magnecor wire. This solved the RPM drop but also checked the ignition noise. It was much less on the left. I have since changed the right also. There is still some noise but it's better. Upon examining the left mag, there was corrosion between the lead wire and the pin that sticks into the wire. The spark was jumping through the corrosion because the resistance from the pin to ground was okay.
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I eventually wound up putting CAMit coils, leads, distributor caps, and ignition leads on my engine - really nice quality and it made things definitely quieter - sad that CAMit closed-up shop recently! I still had a little rf noise when the alternator was charging the battery after take off that would last a few minutes early in each flight. I put a 25V 47000uF capacitor in parallel with the battery and that mostly stopped that! I finally have a very quiet radio!
John
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