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SIDESLIP
Joined: 14 Oct 2012
Posts: 78
Location: CYOO
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 Posted: Sun Nov 04, 2012 4:06 pm Post subject: Radio/Comm issue! Grounding airplane from flying... HELP! |
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Hello all. Just purchased a Homebuilt Zodiac 601XL-B. Rotax 912ULS powered. A200 Radio, Flightcom 403 intercom. Aero flash strobes. The radio is intermittently squealing and tower cannot understand my transmissions. Tried both engine running and not running. Intermittent either way. When it is working, I get 5/5. When it begins squealing, 0/0. Previous owner said he had the same issue with cheaper headsets. Radio worked great, then it didn't. I'm using David Clark 13.2s's. The previous owner has a portable wired in as well, telling me that he's had issues in the past. There is a falcon T/B gyro, Garmin transponder and aero flash strobes. When the strobes are on, the pop of the flash comes thru headsets. I'm really stuck! Bought this plane, and now can't fly it! The rest of the plane is great,, ending runs PERFECT..... But this radio issue has me beat! HELLLP!
Chad
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bryanmmartin
Joined: 10 Jan 2006
Posts: 1018
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| Posted: Tue Nov 06, 2012 2:20 pm Post subject: Radio/Comm issue! Grounding airplane from flying... HELP! |
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You should ground all of your avionics units to the same point on the airframe but each one should have its own separate ground wire running to that point. your lighting circuits and such can share ground wires but the avionics units and many of your engine gauges should not. I have a common grounding point for nearly everything on my airplane. I even have the engine block and battery grounded to this point. The only things that use the airframe as ground are the nav and landing lights.
One more point to remember is this: the shield on your audio transmission lines should not be part of the audio circuit. The audio should line should have a separate wire for signal high and signal low within the same shield. All of the shields on audio transmission lines should be grounded at one end only, not both. It is best to ground all of the shields at the same common point. Usually this means grounding them at the audio panel or intercom panel, whichever is the main hub of the audio system.
This is not to be confused with the shield on radio frequency transmission lines. In this case the shield IS part of the circuit and MUST be grounded on both ends.
The shield on audio lines is to keep stray signals out, the shield on RF lines is to keep the signals in.
The audio low line should not be grounded if it can be avoided. If the audio is returning to the radio through the airframe, all the noise running through the airframe will come through with it. Most head phone and microphone jacks have the audio low line connected to the outer threaded shell of the jack. If these jacks are mounted to the metal airframe they should be installed with insulators to prevent them from grounding out to the airframe.
Some avionics equipment is built with the audio low line grounded to the equipment chassis, in this case you can't avoid grounding the audio. You just have to be extra careful not to ground it anywhere else.
On Nov 6, 2012, at 4:23 PM, SIDESLIP <Chad2007(at)rogers.com> wrote:
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Tim;
I know what you are saying, and I've also had actual personal issues with bad grounds before. Electricity will find the least resistant method of completing a circuit. I've seen it first hand. I haven't had a chance to climb under the dash, as you need to be a contortionist to do so, and it's freezing here. Where my confusion comes in is that almost all of the research I've done says to actually group the grounds together. Avionics together, NAV lights together and so on. So, which do I do? Grounds to same spot / block or to all different places on the airframe? Flightcom says to make the grounds all terminate together. So, you can imagine my confusion. I think a few of the grounds were made by riveting the grounds to the airframe in a few locations. The other challenge is to actually LOCATE all the grounds.
Thanks for your help Tim! It is VERY appreciated!
Chad
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Bryan Martin
N61BM, CH 601 XL,
RAM Subaru, Stratus re-drive.
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Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive. |
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SIDESLIP
Joined: 14 Oct 2012
Posts: 78
Location: CYOO
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| Posted: Thu Nov 08, 2012 7:08 am Post subject: Re: Radio/Comm issue! Grounding airplane from flying... HELP |
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Here are a few "birds nest" photos.
Chad
| | - The Matronics Zenith601-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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| Description: |
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4371 Time(s) |
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| Description: |
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1.64 MB |
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4371 Time(s) |
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C-GYXQ. 912ULS. 601XL-B |
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SIDESLIP
Joined: 14 Oct 2012
Posts: 78
Location: CYOO
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| Posted: Thu Nov 08, 2012 7:13 am Post subject: Re: Radio/Comm issue! Grounding airplane from flying... HELP |
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So, after studying the images I've got, it appears not overly complex. My assumptions are that the braided wires are shielded and the grouping of wires onto those metal blocks are the grounds compiled together. ??
In the image below, it shows a ground of some sort directly to the firewall. Not sure where it goes. Almost impossible to see under dash.
Chad
| | - The Matronics Zenith601-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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4367 Time(s) |
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C-GYXQ. 912ULS. 601XL-B |
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SIDESLIP
Joined: 14 Oct 2012
Posts: 78
Location: CYOO
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| Posted: Fri Nov 09, 2012 7:20 pm Post subject: Re: Radio/Comm issue! Grounding airplane from flying... HELP |
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Anyone???
Chad
Bob? He's the expert?
| | - The Matronics Zenith601-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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