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bobg56

Well Known Member
I've been having an issue with this for the past year. Strangely enough it seems worse during the summer months, when engine not running radio reception is good, when engine is running at idle its ok, however increasing rpm increases the static which is a crackling noise not a whine. When hitting 3500 and over its really difficult to hear other broadcasts clearly. When flying I have to go to idle to hear clearly. I do my CI in June, I replaced my spark plugs and voltage regulator. I have done all the TS I can think of so far, disconnecting ELT antenna to turning off GPS , replacing head phone jacks and insulators, removing antenna and cleaning connections. I have turned off each ignition system, I have completely shut down engine in flight which when doing so completely removes the static. I'm getting ready to change out the antenna coax from RG58 to RG142...today I'm going to re install old spark plugs and put swap out the VR...I've heard of others having this problem but heard of no clear solutions, I'm thinking the coax change will be a big help but also a lot of work. Garmin recommends using RG142 over RG58 so I'm hoping that's the fix. Checked the capacitor on the circuit board as well....anything else to inspect?
 
You may have a grounding or a ground loop problem.
Where are the grounds on the various electrical services?
If they do not all go to the same physical location as the engine ground strap then that may be your problem.
Check the grounds from the voltage regulator and ignition modules to ensure the terminations are secure and the connections are tight.
 
I recently experienced very similar problems and eventually found out it's the alternator. After removing the belt, one can clearly feel there is a play of the alternator shaft. The theory is that the alternator output has some additional ripple due to the play, which caused the noise on the radio and the noise is RPM-related.

After installing a new alternator, the problem is gone.
 
RPM based noise on the Comm is a bit of a challenge. Both ignition and alternator can make noise that changes frequency that follows RPM. Also, your antenna, it's wiring and it's ground also serve to reject noise from the ignition and alternator, so the noise could be completely normal but compromised issues with the antenna are failing to stop it from getting to the receiver.

Suggest loosening the alt belt so that the alt does not spin and do a ground run to see if the noise goes away. If it does, the alter or related components are the culprit. Can't really kill power to the VR with a permanent magnet alt, that I thought the Rotax uses.

Modern ignition use plugs with 5K resistors to keep current down and thus noise. If a plug wire shorts to ground the resistance is gone and current spikes and noise could go above the comm systems ability to reject it. In a 2 plug setup, this can go unnoticed to the untrained person, though often caught during a run up / ign check. Have no idea how this is performed on a Rotax.

142 is nice, but I use 58 for my comms and have no noise issues, just as you didn't until the recent past. the change to 142 is not likely to resolve your issue unless there are issues with the connectors on the current wires.
 
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I have / had noise problems also. I found the problem went away when I put my FlightCom 403 in isolate mode. Isolate mode essentially bypasses the intercom. Lots of filtering on the intercom interface improved things a lot. I don't know where the noise is coming from but I know where it was getting in so that's where I focused my efforts.
 
Yesterday I replaced the VR (Ducotti) with my spare VR (after market Ducotti) did a ground run up to 4500 rpm and there was little to no static however I did not yet do a flight check. What I have noticed is that the yellow generator wire blade connectors tend to show signs of overheating and burning after awhile in service. Even the black sealant on the backside shows bubbling in the area or the generator pins from heat. Its important to make sure they are tight by pinching them a bit before installing. I'm getting ready to dump Ducatti and get the latest greatest VR for the Rotax which I believe is the B&C , hopefully that will end this problem for good. I'll repost the results of my test flight, thanks for all the suggestions.
 
Did you twist the two wires from the Alt to the VR? I know this is best practice from B&C on their PM alt installations and doubt they would recommend it if it didn't help in some way?
 
The Rotax installation has the generator wires shielded...the test flight was not good today, however I was able to understand the transmissions I received although static background noise which followed the throttle. It seems to get worse as the VR warms up, mine is mounted inside cockpit to keep the heat down. Next is to inspect ignition harness , I'm still going to up grade the antenna coax. Garmin recommends using RG142, it's double shielded, hopefully that does the trick.
 
FINALLY solved the problem, I found the two wires (Wht/Blk)which are the shield grounds for the headset wires broke off at the butt splice. This connection is at the Intercom connector plug, it was under the shrink. I imagine that when stowing the wires prior to heat shrinking they got stressed and broke off and out from the butt splice. The wires from the head set do not go to the radio, they go to the intercom first. I also change the radio coax to RG142 which is double shielded. No more static on test flight.
 
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