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Radio Noise on Mag

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Re: Radio Noise on Mag

Postby NigelW » Fri Dec 25, 2015 12:49 pm

Hi All,
Happy Xmas. Still no further progress with the noise. New Ignition units fitted. Avionics?Radio engineer with me all day, new plugs with resistors. The shame is it has seriously curtailed my flying this year although I have also been extremely busy at work and had no time to set to it properly. Got to get it sorted in the new year!
Have a great break everyone and Happy New Year!
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Re: Radio Noise on Mag

Postby diablo » Fri Dec 25, 2015 4:15 pm

Hello Nigel,

There is a number of things that can be tried out. Specialist test kit / equipment (that steve and I have) is required. I am happy to give you a helping hand.

where are you based?

Dean
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Re: Radio Noise on Mag

Postby Steevo » Fri Dec 25, 2015 9:14 pm

Nigel

Are your mag leads that go to your mag switches using shielded cable?

The best wiring scenario for mags is to take single core shielded cable AWG16 and connect the single core from the mag to a terminal on the mag switch. The shield of that wire should connect to an engine earth with the other end of the shield going to the other terminal on the mag switch.

I cannot guarantee that will solve the problem but it will protect the wires from bringing interference in to the cabin.

Where have you put the trig radio main box? Is it in the back as far from the engine as you can get it?

You need to establish if the interference is getting in to the radio or the intercom. If you turn the radio off, can you still hear mag noise (I assume you are using a separate intercom and not the in-built Trig one)?

The mags can transmit interference quite a distance and that's one of the reasons Jab put their antenna in the tail. But there are a few reasons interference can get in to the audio system.

First of all, there is a ground loop. This is where there are multiple grounds for you audio system. Trig are quite bad for this as if you follow their wiring diagrams to the letter, they specify multiple grounds that can go to different places. The reason they do that is for reliability reasons so that if you lose one ground, the radio will still function and will not sustain damage when it is trying to source another ground that it may try and pull through something that cannot provide the power required to run the radio. That's OK in a metal aircraft as the metal helps absorb the interference to some degree. This is good in one respect but bad for interference. Ideally there should be only one secure ground source for all your audio system with single grounds for the devices. All wire should be shielded with the shields only connected at one end and all connected to the same earth point.

All ground wires should be run alongside each other as close as possible. If grounds are separated, then they can take on the job of an antenna which will receive and transmit interference. The mag wires and any power wires that run equipment with motors (electric fuel pump etc) should stay as far away as possible from audio system wires. Create separate bundles for audio and general equipment.

Unfortunately, audio wiring is a very complex topic and requires careful planning to get a noise free system. Some people are lucky and just throw it all in and it works and other people are not so lucky. Different devices are susceptible to different types of interference as they are all designed with different components. The Jab is also a very small space made of fibreglass so there is very little room or options for separating cable properly and no metal structure to act as an interference shield.
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Re: Radio Noise on Mag

Postby NigelW » Sat Dec 26, 2015 5:19 pm

Sorry guys tried to post reply but got an error code.
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Re: Radio Noise on Mag

Postby Steevo » Sat Dec 26, 2015 5:28 pm

Seems to be working ok this end.
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Re: Radio Noise on Mag

Postby NigelW » Sat Dec 26, 2015 5:52 pm

Hi, Trying again on a different machine!
Thanks both for your replies. The main unit is fitted in the 'glove box' area. I am based at Leicester. My problem is that my mind goes completely blank as soon as any form of electronics are mentioned. i have tried to ask for help including the so called avionics engineer who I paid to install it, but keep drawing a complete blank.
I was really keen when I bought the Jab but have hardly flown it since the radio problems. In fact the last outing out I ended squeaking 7600 with D&D calling me when I landed to see if I was OK!
I have always flown with the radio and do not feel comfortable flying without it.
If you guys could find a way of getting to Leicester in the new year sometime I would be more than happy to pay for your services.
Thanks
Nigel
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Re: Radio Noise on Mag

Postby Steevo » Sat Dec 26, 2015 8:12 pm

Nigel

Leicester is not a million miles away from me. I am sure I can find my way up there in the new year and do like a challenge. My one took weeks to get to a noise free system which is why I ended up with so much specialised audio installation equipment (oscilloscope, spectrum analyser, EMI detector etc). Although my issues were for other reasons.

In the meantime, just a couple of things you can do in advance which may give a few clues and rule out anything repetitive. It will also give an idea of what I may need to bring with me.

You say that an avionics professional has looked at and done a lot of the installation. What has he said regarding the issue so far?

I don't suppose you could get some photos of the installation and a wiring diagram if one exists. The glove box, in all honesty, is not the best place for the Trig main unit. Is it the right mag that is causing the interference?

I may have missed something so could you please provide the following information.

Make/Model of intercom if not using the in-built Trig one.
If separate intercom, is there interference with the radio off and just the intercom on?
Has the installation been done using shielded cable?
Does the intercom or radio connect to anything else (music input or audio alerts etc)?
Where are your mic and phone jacks installed?

Steve
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Re: Radio Noise on Mag

Postby NigelW » Sat Dec 26, 2015 9:24 pm

Hi Steevo,
Replied in detail and got error code. I'll get some pics tomorrow and get back with the details.
Many thanks!
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Re: Radio Noise on Mag

Postby Steevo » Sat Dec 26, 2015 9:47 pm

Hi Nigel

If you get an error code again, could you make a note of it or better still take a screenshot. Just in case it is something to do with the site and that gives me a good chance of fixing it.

Steve
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Re: Radio Noise on Mag

Postby NigelW » Sun Dec 27, 2015 10:33 pm

Hi Steevo,
I will do. It's a bit frustrating after typing it all out. I did take the photos but I am away for a few days now. Be back in a few days and will have my Lap Top to hand. Thanks again for your help. Be in touch very soon.
Best Regards Nigel
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