---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 03/07/08: 12 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:23 AM - Coax termination and electrical theory explained. (Eric M. Jones) 2. 06:48 AM - Grounding shielded wires (Speedy11@aol.com) 3. 06:49 AM - Re: Re: "Poor Man's" coax termination with RG-400 (Robert L. Nuckolls, III) 4. 07:07 AM - Re: Re: RG-400 vs. RG-142 (Robert L. Nuckolls, III) 5. 07:08 AM - Re: Coax termination and electrical theory explained. (Ernest Christley) 6. 07:19 AM - Re: Grounding shielded wires (Robert L. Nuckolls, III) 7. 07:43 AM - Re: Coax termination and electrical theory explained. (Robert L. Nuckolls, III) 8. 07:47 AM - Re: Coax termination and electrical theory explained. (Eric M. Jones) 9. 12:08 PM - Ignition/Starter switch wiring (Kevin Klinefelter) 10. 12:12 PM - Re: Re: Coax termination and electrical theory explained. (Robert L. Nuckolls, III) 11. 01:20 PM - Re: Coax termination and electrical theory explained. () 12. 03:11 PM - Re: Coax termination and electrical theory explained. (Henador Titzoff) ________________________________ Message 1 _____________________________________ Time: 06:23:32 AM PST US Subject: AeroElectric-List: Coax termination and electrical theory explained. From: "Eric M. Jones" I have been dabbling with the physics of current moving along a wire. One of the remarkable things about physics that I have to keep re-learning is that seemingly simple phenomena have wildly complicated reasons for working as they do. But understanding these reasons keep us on track . You would think that the theory of electricity has been well worked out by now. But heres your test: 1)What carries the energy in a simple electrical circuit? a-Electrons, b-Holes, c-God knows! 2)What returns on the ground or return wire? a-Electrons, b-Holes, c-God knows! 3)In a coaxial cable, exactly where is the energy carried? a-In the center conductor, b-In the shield, c-God knows! If you answered c for the three questions, you are close to correct but we can shed considerable light on the subject and only a few miracles will be invoked. Lets start with some simple truths: 1) You can't expect electrons to carry energy to the load because a coulomb (a miniscule amount of electrons), a meter from another coulomb electrostatically repel each other with about a million tons of force. (So there's probably some kind of taxpayer-funded DARPA electronic weapon based on this fact in our future....). 2) Electrons dont carry signals or information either because they are far too slow. It takes days for an electron to go a mile. Electromagnetic fields do the job. 3) The notion of ground current as used-up tired electrons slowly returning home to battery rehabilitation is wrong. BOTH the high potential and ground return conductors do identical things, but with opposite polaritieseven in DC circuits. 4) Electrons dont carry energy to the load because they usually dont get there anyway. Most circuits just dont connect power and load in any contiguous way. 5) Coaxial cables are waveguides because the energy transmitted is almost entirely within the inner insulation. An amazing proof of this is that the wave velocity is almost exactly the speed of the electromagnetic wave in the particular material out of which the insulation is made. The importance of this is directly proportional to frequency. For audio purposes it matters little. Skin Effect is a 1957 tribute to Bridgette Bardot, and also what happens to electrons that increasingly drift towards the surface of a conductor at high frequencies. Why do we care about this when electrons dont do much anyway? This is interesting only because the center of conductors at high frequencies have no function. This is easily seen in HF induction coils made of hollow tubing instead of solid. The "pigtails" where the coax shield is twisted into a lead and both the inner conductor and twisted up shield lead are treated as separate wires is deadly to high frequency signals >Megahertz. The shield should be terminated by any method that does not decrease the impedance of the shield or the inner conductor. There are many ways to do this, but they all use some collar arrangement to terminate the messy coax shield. Any coax catalog has lots of solutions. Remember that above a megaHertz, the inner INSULATION carries the bulk of the energy! (As an aside--50 Ohms and 75 Ohms are the impedance of vacuum and air respectively. Early coaxial cables were one or the other.) Bob, in my humble opinion, needs a little nudge on this. Here's how NOT to terminate coaxial cable-- http://aeroelectric.com/articles/shldwire/shldwire.html But yikes....! So it turns out that the simplest DC circuit operation is wildly difficult to explain, but basically the electromagnetic fields carry the energy, not the electrons. They are just there to move and cause the magnetic field. The electrons have only an electric field, and it is only the electrons movement through space that generates a magnetic field. If you followed alongside an electron, you wouldnt see ANY magnetic field. This is the difference between static electricity and the regular stuff. Static electricity has no magnetic field because the electrons arent moving with respect to the observer. http://science.uniserve.edu.au/school/curric/stage6/phys/stw2002/sefton.pdf and if this (excellent!) paper doesn't blow your mind, try-- http://sites.huji.ac.il/science/stc/staff_h/Igal/Research%20Articles/Pointing-AJP.pdf http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part6/page3.html Textbook, Electromagnetics Explained: Part of the EDN Series for Design Engineers by Ron Schmidt -------- Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge, MA 01550 (508) 764-2072 emjones@charter.net Read this topic online here: http://forums.matronics.com/viewtopic.php?p=168228#168228 ________________________________ Message 2 _____________________________________ Time: 06:48:28 AM PST US From: Speedy11@aol.com Subject: AeroElectric-List: Grounding shielded wires I know - the subject's been covered before. And yes, I know - it's in the archives. But, I can't find it in the archives and I'd appreciate some help. I'm getting conflicting advice from the radio harness maker and from the intercom maker regarding the grounding of shielded wires. One tells me to ground the shield on only one end while the other says to ground both ends. Who to believe? My situation: SL30 with professionally wired harness. Shields are all grounded on the radio chassis. I'm building the harness for the intercom. The intercom instructions show shielding grounded at both ends only on the audio wires. However, email from intercom maker says to ground both ends of all shielded wire. 1. Should shielded wires from SL30 to intercom be grounded at both ends? 2. Should those grounds be ganged together to connect to the single ground pin on the intercom? 3. Should mic phone plug wire shields be grounded at both ends? 4. Should headphone plug wire shields be grounded at both ends? 5. Should all shields be ganged together to connect to the single ground pin on the intercom? Stumped, Stan Sutterfield **************It's Tax Time! Get tips, forms, and advice on AOL Money & Finance. (http://money.aol.com/tax?NCID=aolprf00030000000001) ________________________________ Message 3 _____________________________________ Time: 06:49:43 AM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: RE: "Poor Man's" coax termination with RG-400 At 04:58 PM 3/6/2008 -0800, you wrote: > >While we're on the topic of coax and RG-400....what would you guys recommend >as to a wire stripper tool? I got the Ideal Stripmaster for stripping >regular wire but need something for coax. > >And while we're on wire...what would you recommend for a crimper? My personal favorite stripper is offered by Gilchrist Electric at: http://www.gilchrist-electric.com/3-blade-coax-cable-strip.php They used to have an Ebay store but seem to have split the sheets with Ebay. The link above goes directly to their website. This is a 3-blade tool that comes with the appropriate sized allen wrench to effect adjustment of cutting depth for each blade. See the 3-Blade Stripper pictures at: http://www.aeroelectric.com/Pictures/Tools/Wire_Strippers/ I presume you're asking about coax crimpers . . . for BNC connectors, you need a high-leverage, hard-die tool with 0.068" and 0.213" pockets. This tool offered by Radio Shack is one option: http://tinyurl.com/ys7oed as is the RCT-2 offered by http://bandc.biz For the pre-insulated ring terminals, consider this tool: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93977 Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ---------------------------------------- ________________________________ Message 4 _____________________________________ Time: 07:07:50 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: RG-400 vs. RG-142 At 10:19 PM 3/6/2008 -0500, you wrote: > >I think I asked the same question awhile ago Bill but 11 feet seems to >work fine on a GTX320 despite the 8.8 foot caution. >Ken > >Bill Bradburry wrote: >> >>I installed my transponder antenna about 6 months ago in the rear of my >>plane. Now I am getting ready to install the transponder itself. While >>reading the instructions, I discovered that the max distance for RG400 is >>8.8 feet. My installation is probably 10 feet. Do I need to move the >>antenna? If I don't move it, what will be the down side? It is a Garmin >>GTX327 if that matters.. >>Bill B When a manufacturer publishes performance specifications for a product, they need to state the boundaries on installation variables that influence the numbers. In the case of 8.8' max length, they're only saying that performance will be degraded from the published specifications if that length is exceeded. What is not so apparent is whether or not a user/observer would be aware of the degradation . . . and in this case, the answer is no. There's enough head-room in the receiver's capability to deliver useful performance in spite of an additional 0.1 Db or so of feedline losses. Now, if you were installing this radio in a 787 and needed to put the antenna out on a wing tip, a higher performance coax cable would be a really good idea. Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ---------------------------------------- ________________________________ Message 5 _____________________________________ Time: 07:08:06 AM PST US From: Ernest Christley Subject: Re: AeroElectric-List: Coax termination and electrical theory explained. Eric M. Jones wrote: > Bob, in my humble opinion, needs a little nudge on this. Here's how NOT to terminate coaxial cable-- > > http://aeroelectric.com/articles/shldwire/shldwire.html > The difference between theory and practice is that in theory they are the same. You have two copper strips to form an antennae. One must be connected to the center conductor, the other to the shield. Whether you terminate the coax with some fancy, expensive solution from an electronics catalogue or Bob's method, at some point the center conductor has to split out from the shield. The difference in actual performance in the flying airplane will be lost in the noise (pun intended). In theory, there is an advantage in the expensive, complicated solution. In practice, the advantage ain't worth the headache. ________________________________ Message 6 _____________________________________ Time: 07:19:15 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Grounding shielded wires At 09:44 AM 3/7/2008 -0500, you wrote: >I know - the subject's been covered before. And yes, I know - it's in the >archives. >But, I can't find it in the archives and I'd appreciate some help. >I'm getting conflicting advice from the radio harness maker and from the >intercom maker regarding the grounding of shielded wires. One tells me to >ground the shield on only one end while the other says to ground both >ends. Who to believe? >My situation: SL30 with professionally wired harness. Shields are all >grounded on the radio chassis. >I'm building the harness for the intercom. The intercom instructions show >shielding grounded at both ends only on the audio wires. However, email >from intercom maker says to ground both ends of all shielded wire. > >1. Should shielded wires from SL30 to intercom be grounded at both ends? >2. Should those grounds be ganged together to connect to the single ground >pin on the intercom? >3. Should mic phone plug wire shields be grounded at both ends? >4. Should headphone plug wire shields be grounded at both ends? >5. Should all shields be ganged together to connect to the single ground >pin on the intercom? Follow the instructions. If the wiring diagram provided by the manufacturer SHOWS a ground connection at both ends, then there's a reason for it an the designer's intentions should be observed. However, the general rule of thumb is that shields are to be GROUNDED at one end only . . . that doesn't mean that the shield is not CONNECTED at both ends . . . the shield may have an important role to play with respect to signal or power return paths. A very common double-grounding error in aircraft audio systems occurs when headset and microphone jacks are allowed to find local ground at the point of attachment to the airframe. This is why insulating washers . . . http://www.aeroelectric.com/Pictures/Connectors/Audio/Jack_Insulation_Washers.jpg are recommended where the jacks are to me mounted to a conductive location on structure. The schematic for wiring the product should be quite explicit as to where the shields are connected. Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ---------------------------------------- ________________________________ Message 7 _____________________________________ Time: 07:43:39 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Coax termination and electrical theory explained. At 06:19 AM 3/7/2008 -0800, you wrote: > >I have been dabbling with the physics of current moving along a wire. One >of the remarkable things about physics that I have to keep re-learning is >that seemingly simple phenomena have wildly complicated reasons for >working as they do. But understanding these reasons keep us on track . >You would think that the theory of electricity has been well worked >out by now. But heres your test: > > 1)What carries the energy in a simple electrical circuit? > a-Electrons, > b-Holes, > c-God knows! >Bob, in my humble opinion, needs a little nudge on this. Here's how NOT to >terminate coaxial cable-- > >http://aeroelectric.com/articles/shldwire/shldwire.html > >But yikes....! So it turns out that the simplest DC circuit operation is >wildly difficult to explain, but basically the electromagnetic fields >carry the energy, not the electrons. They are just there to move and cause >the magnetic field. The electrons have only an electric field, and it is >only the electrons movement through space that generates a magnetic field. >If you followed alongside an electron, you wouldnt see ANY magnetic >field. This is the difference between static electricity and the regular >stuff. Static electricity has no magnetic field because the electrons >arent moving with respect to the observer. Eric my friend . . . you're making this far more complex than it needs to be. Yes, the physics of conducting electrical energy from one place to another have been studied, quantified and explained for a century or so. However, there ARE practical departures from "ideal" that do not materially affect performance. Super-simple VHF COMM antennas were installed by the tens of thousands in light aircraft using the technique illustrated. Yes, the effects on SWR, radiation patterns, and radiation efficiency were degraded from ideal . . . but the the ideal was never perfect either. For the frequencies of interest (118 - 135 Mhz), effects of the 1" or so of non-coaxial conductor that results from the use of terminals on pigtails was barely noticeable in the lab and never noticed by a pilot in an airplane. Now, the effects of this technique at transponder frequencies is much larger . . . easily measured in the lab. But with some judicious refinement of fabrication technique to get the shortest possible leads (below 1/2") the effects on real time performance were not observable. When we go to the lab to make calibrated measurements of performance, the obvious goal is to minimize the effects of test-setup error. In this environment we strive for the-best-we-know-how-to-do with the goal of suppressing sum of all test errors to less than 1/4 that of the phenomenon being measured. But in the real world of talking to Flight Watch from an RV, well considered departures from the best-we-know-how-to-do don't reflect badly upon our craftsmanship. Bob . . . ________________________________ Message 8 _____________________________________ Time: 07:47:43 AM PST US Subject: AeroElectric-List: Re: Coax termination and electrical theory explained. From: "Eric M. Jones" > The difference in actual performance in the > flying airplane will be lost in the noise (pun intended). In theory, > there is an advantage in the expensive, complicated solution. In > practice, the advantage ain't worth the headache. Maybe, maybe not. It depends on the details. But you have not tested it, (nor has Bob). I submit that when the HANDY SHORT-CUT solution is proposed as the GENERAL solution, the best interests are not well served. The coax terminations in electronics catalogs are neither difficult nor complicated. Furthermore you can make you own in a pinch. So there are two choices: 1) The right way. 2) The other way. -------- Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge, MA 01550 (508) 764-2072 emjones@charter.net Read this topic online here: http://forums.matronics.com/viewtopic.php?p=168247#168247 ________________________________ Message 9 _____________________________________ Time: 12:08:55 PM PST US From: Kevin Klinefelter Subject: AeroElectric-List: Ignition/Starter switch wiring Bob and all, I have a couple questions. I am wiring a Rotax 914 in my Europa per Z-16(sort of). I want to use a switch for each "mag" that will be down-off, middle-on, momentary-up of both to start. Is there a drawing somewhere on the site that shows how to wire this? I also want to wire a switch to control two alternators, the rotax built dynamo and a Denso IR alternator mounted on the vac pad. I would like to use one switch; down-dynamo middle-off and up-main alternator(denso).Is there a drawing showing how to wire that? Thanks, Kevin ________________________________ Message 10 ____________________________________ Time: 12:12:55 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Coax termination and electrical theory explained. At 07:42 AM 3/7/2008 -0800, you wrote: > > > > The difference in actual performance in the > > flying airplane will be lost in the noise (pun intended). In theory, > > there is an advantage in the expensive, complicated solution. In > > practice, the advantage ain't worth the headache. > > >Maybe, maybe not. It depends on the details. But you have not tested it, >(nor has Bob). ???? I've made a good living for over 40 years delivering products to a customer's needs and in many cases, verifying performance both in the lab and in the customer's application. For you to make ANY assertions about what I have or have not learned by experiment, or success of myself and colleagues in the field is specious and without foundation. > I submit that when the HANDY SHORT-CUT solution is proposed as the > GENERAL solution, the best interests are not well served. You extrapolate much floobydust from the original question. The goal was to make an electrically adequate connection between a coax feedline and the classic stone-simple, rod-on-a-feedthru comm antenna. This style antenna is still offered by many suppliers not the least of which is . . . http://www.chiefaircraft.com/Aircraft/Antennas/Images/AS_AV534.jpg and yields 76 hits on a Google search. So, returning to the original question, what are your recommendations for attaching a coax to this product? Further, if your recommendations involve extensive $time$ to satisfy some goals for transmission line matching or keeping the holes separated from the electrons, what's the expected return on investment for making that effort? You should know that the last time I designed one of these antennas into an installation, I discarded the large ring-terminal intended for shield braid connection to airframe (large area, low pressure) in favor of the PIDG ring terminal (small area, high pressure) connection of the shield to the airframe. What we were discussing was NOT a SHORT-CUT as a GENERAL solution but a well considered, time tested, current marketplace practice to a very SPECIFIC application. >The coax terminations in electronics catalogs are neither difficult nor >complicated. Furthermore you can make you own in a pinch. So there are two >choices: > >1) The right way. >2) The other way. There are MANY ways to work toward design goals. Some perform better, some most more, some are not possible to implement in the present situation. The hallmark of craftsmanship is achieving the best solution to the task of the moment with resources at hand. Bob . . . ________________________________ Message 11 ____________________________________ Time: 01:20:32 PM PST US Subject: RE: AeroElectric-List: Coax termination and electrical theory explained. From: Holy cow, I just want to talk on the radio. I've got a plastic airplane so I just snip off the ends and throw them away. Radio works great - all 3 of them. You guys are splitting hairs over a stupid cable 8 feet long (if that). What are you flying, 747's? I'll bet my radio would send/receive just as well using some RJ6 leftover from my satellite installation. Do Not Archive -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: Friday, March 07, 2008 10:38 AM Subject: Re: AeroElectric-List: Coax termination and electrical theory explained. --> At 06:19 AM 3/7/2008 -0800, you wrote: >--> > >I have been dabbling with the physics of current moving along a wire. >One >of the remarkable things about physics that I have to keep re-learning is >that seemingly simple phenomena have wildly complicated reasons for >working as they do. But understanding these reasons keep us on track . >You would think that the theory of electricity has been well worked >out by now. But heres your test: > > 1)What carries the energy in a simple electrical circuit? > a-Electrons, > b-Holes, > c-God knows! >Bob, in my humble opinion, needs a little nudge on this. Here's how NOT >to >terminate coaxial cable-- > >http://aeroelectric.com/articles/shldwire/shldwire.html > >But yikes....! So it turns out that the simplest DC circuit operation >is >wildly difficult to explain, but basically the electromagnetic fields >carry the energy, not the electrons. They are just there to move and cause >the magnetic field. The electrons have only an electric field, and it is >only the electrons movement through space that generates a magnetic field. >If you followed alongside an electron, you wouldnt see ANY magnetic >field. This is the difference between static electricity and the regular >stuff. Static electricity has no magnetic field because the electrons >arent moving with respect to the observer. Eric my friend . . . you're making this far more complex than it needs to be. Yes, the physics of conducting electrical energy from one place to another have been studied, quantified and explained for a century or so. However, there ARE practical departures from "ideal" that do not materially affect performance. Super-simple VHF COMM antennas were installed by the tens of thousands in light aircraft using the technique illustrated. Yes, the effects on SWR, radiation patterns, and radiation efficiency were degraded from ideal . . . but the the ideal was never perfect either. For the frequencies of interest (118 - 135 Mhz), effects of the 1" or so of non-coaxial conductor that results from the use of terminals on pigtails was barely noticeable in the lab and never noticed by a pilot in an airplane. Now, the effects of this technique at transponder frequencies is much larger . . . easily measured in the lab. But with some judicious refinement of fabrication technique to get the shortest possible leads (below 1/2") the effects on real time performance were not observable. When we go to the lab to make calibrated measurements of performance, the obvious goal is to minimize the effects of test-setup error. In this environment we strive for the-best-we-know-how-to-do with the goal of suppressing sum of all test errors to less than 1/4 that of the phenomenon being measured. But in the real world of talking to Flight Watch from an RV, well considered departures from the best-we-know-how-to-do don't reflect badly upon our craftsmanship. Bob . . . ________________________________ Message 12 ____________________________________ Time: 03:11:36 PM PST US From: Henador Titzoff Subject: Re: AeroElectric-List: Coax termination and electrical theory explained. I hate to say this, but just because it works for you doesn't mean that it's going to work for everyone else. I would follow the manufacturer's recommendations and even improve upon it if possible. Henador Titzof ----- Original Message ---- From: "longg@pjm.com" Sent: Friday, March 7, 2008 4:15:52 PM Subject: RE: AeroElectric-List: Coax termination and electrical theory explained. Holy cow, I just want to talk on the radio. I've got a plastic airplane so I just snip off the ends and throw them away. Radio works great - all 3 of them. You guys are splitting hairs over a stupid cable 8 feet long (if that). What are you flying, 747's? I'll bet my radio would send/receive just as well using some RJ6 leftover from my satellite installation. Do Not Archive Never miss a thing. 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