Zenith Aircraft Builders and Flyers
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New rf Noise!
I've got about 325 hrs on my STOL CH750/Jabiru 3300. My radio (MGL V6) has been relatively (rf noise) quiet for most of those hours. The Jab 3300 came with quality rf suppressive plug wires - I added Iridium resistor plugs and upgraded the Honda magneto coils with Magnecor rf suppressive leads and this gave me a relatively quiet installation, as far as the radio is concerned!
Lately, however, a new rf gremlin has appeared. The radio is dead quiet during the engine warm-up. Upon takeoff, I get a "Brap!" static noise sound that lasts about as long as it takes to say "Brap!" This may occur in irregularly spaced bursts of 2, 3, or more and then a few seconds later, occur again. Curiously, it seems to continue for the first few minutes of flight and then gradually fades away and is completely gone after 15-20 minutes. If I switch the ignition to "left," it completely kills the noise. If I switch it to "right," it markedly reduces the noise but I "think" I can still hear it. Only when on "both" is it loud and annoying.
The Jabiru 3300 has a unique alternator in that it does not produce charging current until approximately 1900 rpm, so it doesn't produce significant output until full throttle at takeoff. It has been suggested to me that a weak battery, requiring more charge, could be triggering the voltage regulator to make the noise. But, I have a relatively new EarthX lithium battery and it is quite strong and not "weak!"
I have the magnetos' p-leads' shields grounded at the magnetos and not at my ACS switch. The ACS switch's center ground is grounded to the airframe. To the best of my recollection, I've not changed or modified anything electrical recently. I'm at a loss to explain why this noise is just now appearing! Makes one wonder if something is "aging" and failing. Does a bad voltage regulator get "rf noisy?" It appears to be working perfectly as far as maintaining battery charge, etc.
Any ideas?
John
N750A
Replies to This Discussion
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Permalink Reply by John Austin on
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Hi Wayne,
Here's where I am now:
I did a test hop with the voltage regulator completely out of the circuit and the noise persisted.
I soldered the alternator output leads and installed a terminal strip to eliminate the multi-pin connector to the voltage regulator and the noise persisted.
THEN, I finally (duh!) suppressed the squelch and determined the background rf noise was much louder than it used to be - why, I haven't a clue! Turning up the squelch helps to some degree, but there's a lot of noise when listening to weak/distant transmissions - this is all like it used to be when the engine was new and before I tweaked the ignition with ferrite cores and modified the coils with spiral-wound leads to the distributor.
SO, when I was at AirVenture, I looked at the CAMit engine (very similar to Jabiru 3300 and most parts are interchangeable) and noticed the very good quality spiral-wound coil leads and spiral-wound ignition wires on the engine. I've got this nagging fear that my coil conversion might be breaking-down, causing the noise. I also think the CAMit spark plug wires are better quality than what I have, SO I've ordered a set of CAMit distributor caps, coils with leads, and ignition wires! These should arrive in a couple of weeks and we'll see if they're quieter!
John
N750A
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Permalink Reply by Wayne Tyson on
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What a drag! I'd be glad to describe your problem to an electronic "genius" I know if you like.
Wayne
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Permalink Reply by christopher fryatt on
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on a way out theory...... you don't happen to also have garmin 796 and gdl set-up? I have similar noises that some say relates to garmin recharge of internal battery when hardwired.
corvair engine
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No, no Garmin equipment at all!
I've determined that the overall rf ignition noise has increased and is breaking through the previous squelch setting. I had modified some coils with rf suppressive spiral-wound distributor leads and now am worried that perhaps my connection is breaking down, so I'm replacing both coils (with integral leads) and also the plug wires while I'm at it with quality ones from CAMit - all their wires are spiral-wound and look to be very high quality!.
Stay tuned ...
John
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Some pun! I'm standing by . . .
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Permalink Reply by Bill Bear on
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Hi John,
I know this is an old thread, but I am curious...what was the FIX? Did your new coils and plug wires solve the noise problem?
Bill Bear
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Yes, the new coils and wires, along with resistor plugs, greatly reduced the rf noise. Radio is still scratchy on very distant transmissions but at 750 STOL speeds, local transmissions, which are loud and clear, are the only ones I need to hear! LOL!
John
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Permalink Reply by Guy Zindel on
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We had no issues in my old plane but the second my buddy plugged in his Dave Clarks.... The system went nuts with static.
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