radio noise

·         rob brown

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I have just fitted a new 833 radio and I am getting very load rev related noise, I have identified that the right mag is at fault as when turned off the reception is interference free, Model is j430, has anyone else experienced this problem before, The radio it replaced was a Microair and I have always has rev related noise but its worse now. any help would be most apreciated.
Regards Rob Brown

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·         Doug Smith

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Hi Rob,

What's the make of your new radio?

Basic health checks of your electrical and ignition systems are the first place to start with radio noise: make sure the plug gaps and coil gaps are right, the distributor and rotor are in good shape, the plug leads are undamaged and the terminals at their ends tight... from there, depending on the age of your J430, it may not have the later noise-suppressing features to the electrical system: shielded wires to the ignitions, ferrite beads on the wiring looms and VHF antenna. They're shown in the schematic in the Technical Manual but happy to walk you through them.

Regards,
Doug.

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·         rob brown

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Thanks for the promt reply Doug, the radio is a trig ty91 and the plane is 10 years old, as mentioned before the interference is on the right mag,
i am not good with electrics and any advice should be phrased as if talking to five year old, sounds like shielding is the answer, any help would be most apreciated.
Kind Regards Rob

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·         Doug Smith

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Hi Rob,
Unfortunately RF noise can be a huge pain to locate and control. It sounds like you've got it located in the ignition so I'll bypass any advice on instruments, avionics etc (which can all cause problems of their own!).

I'm having some trouble attaching the wiring diagram so I'll email it to you. It's the one on page 268 of the airframe technical manual anyhow.

After making sure of the coil gaps etc, the next thing to try is adding some ferrite suppressors to the system: you can see on sheet 1 that wherever a wire goes through the firewall there is a ferrite suppressor fitted. You can get these from places like Jaycar. We use the ones that are split, in a little plastic housing, so you can just clamp them over the wire bundles. The ferrite tends to damp high frequency signals in wires, and so reduce RF noise a bit.

I've also found that ferrite toroids on the radio antenna help. Page 86 of the J160 construction manual shows how they get fitted to the aft end of the VHF antenna. Similar to the ferrite suppressors above, these help damp out RF noise in the antenna and make the antenna work better with the radio (better SWR).

Next we get into the realm of swapping wires... in particular, the ignition wires: in the upper right corner of sheet 1. In this configuration we use a single core, shielded wire for each ignition wire. Connect the wire itself to the terminal on the coil, connect the shield of the wire to the engine and then connect the ignition switch to the wire and shield - when that switch is closed it will earth the coil and kill the spark. That arrangement means that the ignitions aren't actually connected to the aircraft electrical system at all and tends to reduce the amount of nose in the system.

Those are the relatively easy items... Using shielded wire on all the headset wires can also help a lot, but it's a pretty big job to change that out, and from there we really get into the areas it'd be best to leave to a qualified technician...

Hope that helps!

Regards,
Doug.

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·         Doug Smith

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Email from Rob:
Hi Doug. I have sorted the noisy radio.
The left mag was the problem, I put a new wiring loom back to mag switch in screened wire and run wires away from the other bundles, perfect now.
Thank you for your help
Regards Rob Brown

Nice one Rob, good outcome.
Regards,
Doug.