AeroElectric-List Digest Archive

Sat 07/02/11


Total Messages Posted: 11



Today's Message Index:
----------------------
 
     1. 07:29 AM - Re: Re: a bit O/T ...AEA Responds (Robert L. Nuckolls, III)
     2. 07:32 AM - Re: Antenna static discharge protection (Robert L. Nuckolls, III)
     3. 09:48 AM - Ground loops (John Grosse)
     4. 11:08 AM - Re: Ground loops (Robert L. Nuckolls, III)
     5. 11:14 AM - Re: Ground loops (Robert L. Nuckolls, III)
     6. 11:15 AM - Re: Ground loops (Charlie England)
     7. 01:17 PM - Re: Ground loops (John Grosse)
     8. 01:38 PM - Re: power line interferances (James Robinson)
     9. 02:34 PM - Re: power line interferances (Robert L. Nuckolls, III)
    10. 03:35 PM - Re: Ground loops (Robert L. Nuckolls, III)
    11. 05:59 PM - WxWorx REWX9ID USB Weather Receiver For Sale... (Matt Dralle)
 
 
 


Message 1


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    Time: 07:29:51 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: a bit O/T ...AEA Responds
    >Perhaps we can get together some time & pursue it, either in person >or on Bob's potential new politics list. I'm working with Matt to fix some bugs in the list-server engines I mentioned. When Matt has some spare time, he'll get them squared away. At that time, I'll invite anyone who desires to join a discussion group for what I'll call Simple-Ideas. An exploration of fundamental truths that transcends politics (but is often stirred in with politics). Subscription to these lists is by request/invitation. I maintain the registered address lists manually for now . . . as opposed to the user management system that supports this list. Will let you all know when it's up and running. Bob . . .


    Message 2


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    Time: 07:32:15 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Antenna static discharge protection
    At 10:40 PM 7/1/2011, you wrote: >Ah! I hadn't considered a shunt inductor! > >Thanks for the info! If anyone else knows where to find data on in >flight ESD I'd still love to see it. We had a big shake-up at Beech about 25 years ago to deal with some static discharge wick issues on the fleet. There are pretty simple bench tests to test the relative effectiveness of a static wick. I'm aware of no flight test data . . . you might poke around in the patents (freepatentsonline.com) and NASA documents. Bob . . .


    Message 3


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    Time: 09:48:36 AM PST US
    From: John Grosse <grosseair@comcast.net>
    Subject: Ground loops
    I think I understand about avoiding ground loops by providing only a single path to ground, but I'm confused by the fact that the avionics manufacturers (Garmin and PS Engineering in particular) tell you to ground both ends of a shielded cable. Specifically, when going from a mic or phone input to the audio panel or going from a com radio to the audio panel all the wiring diagrams show the shield grounded at both ends. Doesn't this create a ground loop? Can someone please enlighten me. John Grosse


    Message 4


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    Time: 11:08:35 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Ground loops
    At 11:43 AM 7/2/2011, you wrote: > >I think I understand about avoiding ground loops by providing only a >single path to ground, but I'm confused by the fact that the >avionics manufacturers (Garmin and PS Engineering in particular) >tell you to ground both ends of a shielded cable. Specifically, when >going from a mic or phone input to the audio panel or going from a >com radio to the audio panel all the wiring diagrams show the shield >grounded at both ends. Doesn't this create a ground loop? If they are grounded to different locations . . . absolutely. I am increasingly mystified by the instructions from folks who should know better are mis-using shields over wires . . . and especially 'grounding both ends' when the shield is NOT being used as a signal path. Here's an example of an audio system using NO shielded wires. It also takes potential for ground loops into account with note 2. http://www.aeroelectric.com/PPS/Audio/2000014C.pdf Here's a drawing I produced where shields ARE part of the signal pathways. Note specific treatment callouts for shields at both ends. http://www.aeroelectric.com/PPS/Audio/DualCommAudio.pdf Same thing here . . . http://www.aeroelectric.com/PPS/Audio/hv1_760vhf.pdf >Can someone please enlighten me. If the shield over a wire is ALSO a signal path, i.e. the 'ground' connection for a remotely mounted mic or headset jack, then that shield goes to ground at ONE END ONLY which will be the "lo" side of that feature AT THE INTERCOM or RADIO's ground . . . which in turn is taken to the instrument panel ground for extension to aircraft ground as illustrated in Z-15. You can have LOTS of grounds if they are strung out in a planned, linear fashion. The "loop" happens when a conductor operating at ground is tied to the airframe in more than one place . . . when that structure carries potentially antagonistic 'noise currents'. Suggest you review http://www.aeroelectric.com/articles/richter/response_1.pdf http://www.aeroelectric.com/articles/richter/response_2.pdf by searching on the word 'shield' in these two documents and then review the context in each case. The 'Richter Affair' was some years back but it seems that many individuals have the same mis-conceptions in common about shields. It's a sad day when the installers instructions are not well thought out. Bob . . . Bob . . .


    Message 5


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    Time: 11:14:10 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Ground loops
    At 11:43 AM 7/2/2011, you wrote: > >I think I understand about avoiding ground loops by providing only a >single path to ground, but I'm confused by the fact that the >avionics manufacturers (Garmin and PS Engineering in particular) >tell you to ground both ends of a shielded cable. Can you point me to wiring diagrams on the 'net that speak to this? Bob . . .


    Message 6


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    Time: 11:15:28 AM PST US
    From: Charlie England <ceengland@bellsouth.net>
    Subject: Re: Ground loops
    On 07/02/2011 11:43 AM, John Grosse wrote: > <grosseair@comcast.net> > > I think I understand about avoiding ground loops by providing only a > single path to ground, but I'm confused by the fact that the avionics > manufacturers (Garmin and PS Engineering in particular) tell you to > ground both ends of a shielded cable. Specifically, when going from a > mic or phone input to the audio panel or going from a com radio to the > audio panel all the wiring diagrams show the shield grounded at both > ends. Doesn't this create a ground loop? > > Can someone please enlighten me. > > John Grosse Hi John, One thing to remember is that for signals in an unbalanced circuit, 'ground' is usually referring to the return path to complete a circuit. The return is usually at 'ground' potential, but in some circuits, it might not be. A ground 'loop' is actually having 2 different paths for the ground, as you say. In most audio circuits, the shield is used for the return path. With the mic circuit, the mic jack is almost always specified as isolated from the airframe to avoid that 2nd return path. The radio to audio panel issue is a bit harder to reconcile with the 'rule', but signal levels are higher there & the shield path is typically so short that secondary return paths don't seem to be as much of an issue. If you allow one end of the shield to float, and let the return find its own path through the airframe, I'd bet that you'd be creating the kind of problems that the 'rule' is trying to prevent. That's not a very satisfying answer, I know. Maybe someone else can give a more technically specific answer. Charlie


    Message 7


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    Time: 01:17:36 PM PST US
    From: John Grosse <grosseair@comcast.net>
    Subject: Re: Ground loops
    Thanks for the responses. I misspoke about PS Engineering. They ground the shield at one end, but here's the diagram for a Garmin SL40: You'll notice that they specifically say to ground both ends of the shield to the case. John > ------------------------------------------------------------------------ > > Robert L. Nuckolls, III <mailto:nuckolls.bob@aeroelectric.com> > July 2, 2011 1:11 PM > > > <nuckolls.bob@aeroelectric.com> > > > Can you point me to wiring diagrams on the 'net that > speak to this? > >


    Message 8


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    Time: 01:38:01 PM PST US
    From: James Robinson <jbr79r@yahoo.com>
    Subject: Re: power line interferances
    Hi Bob I have talked to you before about my needing to move the batteries in my Glasair 111 from the firewall to behind the baggage compartment. My latest problem with this conversion is the routing of the 2 #2s and 2 #4s. To run down the center console there are a lot of things running in that area, but there may be enough room. The other option is to go under the wing, but that has it's problems as well. There is minimum room between the bottom of the wing and the belly panel, and a VOR antenna is in the way. My main question is: Are there potential problems I need to factor into the equation as to where these big wires run in relationship to the other wires and antennas. Any suggestions or ideas. Jim James Robinson Glasair lll N79R Spanish Fork UT U77


    Message 9


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    Time: 02:34:47 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: power line interferances
    At 03:35 PM 7/2/2011, you wrote: >Hi Bob >I have talked to you before about my needing to move the batteries >in my Glasair 111 from the firewall to behind the baggage >compartment. My latest problem with this conversion is the routing >of the 2 #2s and 2 #4s. Why two #4. The two batteries can share a single #2 ground. > To run down the center console there are a lot of things running > in that area, but there may be enough room. The other option is to > go under the wing, but that has it's problems as well. There is > minimum room between the bottom of the wing and the belly panel, > and a VOR antenna is in the way. My main question is: Are there > potential problems I need to factor into the equation as to where > these big wires run in relationship to the other wires and > antennas. Any suggestions or ideas. Run them all together. There are no proximity issues with respect to other wires/accessories. Bob . . .


    Message 10


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    Time: 03:35:22 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Ground loops
    At 03:13 PM 7/2/2011, you wrote: >Thanks for the responses. >I misspoke about PS Engineering. They ground the shield at one end, >but here's the diagram for a Garmin SL40: You'll notice that they >specifically say to ground both ends of the shield to the case. > >John Okay, I'll bet you a dollar to a donut that the "audio grounds" connected with wires are internally grounded to chassis on both devices. Adding a shield over a twisted pair adds no benefit for two devices located next to each other. In this case, adding shields and grounding at both ends is only redundant to the ground-to-ground wire . . . hence, no risk. You could just as easily wire these boxes up with twisted pairs and no shields. <ceengland@bellsouth.net> The radio to audio panel issue is a bit harder to reconcile with the 'rule', but signal levels are higher there & the shield path is typically so short that secondary return paths don't seem to be as much of an issue. If you allow one end of the shield to float, and let the return find its own path through the airframe, I'd bet that you'd be creating the kind of problems that the 'rule' is trying to prevent. I think the potential is already there with the 'audio grounds' If the radio were, say, in a rear cockpit and the audio panel in front . . . and the battery grounds were in the tail, then there is potential for ground loop coupling whether or not a shield is present. That's not a very satisfying answer, I know. Maybe someone else can give a more technically specific answer. Most general aviation systems make prolific use of chassis ground for both power and signals within any given device. This generally not a problem for small aircraft . . . especially when we go to some pains to avoid noisy circuits circulating on the airframe. Military stuff uses chassis ground only for shielding where LOCAL bonding to airframe is desirable. RFI filters grounded to chassis bring signal and power wires in to dedicated, floating grounds within the device. This makes is MUCH easier to manage ground systems. So I guess I'd have to continue to say there are no hard 'rules' for handling shields because we seldom are privy to wiring details inside the black boxes. If the schematic John provided us was for some really 'advanced' equipment, those paired audio lines would be true balanced pairs and only one "low side" would be grounded internally to inside the source box. The load end would be totally floating with a ton of common mode rejection. Shielding would still be of no particular benefit. All we can do is the best guess and then go after a noise problem should it happen to pop up. Our best guess is adequate probably 99% of the time. What we can say for sure is that all the schematics showing shields that are not part of a return path could easily be replaced with a wire. Shielding has essentially zero probability of added value in our working environment. Bob . . . Bob . . .


    Message 11


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    Time: 05:59:42 PM PST US
    From: Matt Dralle <dralle@matronics.com>
    Subject: WxWorx REWX9ID USB Weather Receiver For Sale...
    I have a 1-year old WxWorx REWX9ID USB XM Aircraft Weather and XM Audio receiver for sale. It was just removed from my RV-8 and is in perfect working order. Includes Antenna, Mount, Receiver Unit, and USB Interface. It is compatible with the Grand Rapids EFISs and a number of others. Gives text and graphical representations of weather including Rain, Wind, Temp, etc. Requires separate monthly XM subscription which is not included in this offering. Attached are some pictures of the actual unit for sale. Works great and I wouldn't fly without a similar product. I'm replacing the functionality with an ADS-B receiver. Additional information on the unit can be found here: https://www.wxworx.com/portable-receiver-overview https://www.wxworx.com/interface-modules Aircraft Spruce has the unit for $595: http://www.aircraftspruce.com/catalog/avpages/fl190True.php I will take $400 firm for the unit as shown plus $10 for shipping. First come, first served. Email me with questions. I can accept PayPal http://www.paypal.com using "dralle@matronics.com" or I can accept Visa/MC directly. I will take a 2.5% discount for a check, but it will have to clear before I ship. Best regards, Matt Dralle - Matt Dralle RV-8 #82880 N998RV "Ruby Vixen" http://www.mattsrv8.com - Matt's Complete RV-8 Construction Log http://www.mattsrv8.com/Rebuild - Post Landing Mishap Rebuild Log http://www.youtube.com/MattsRV8 - Matt's RV-8 HDTV YouTube Channel Status: 170+ Hours TTSN - Rebuilding Fuselage After Landing Mishap...




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