---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 01/26/11: 20 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:00 AM - Re: vor antenna (BobsV35B@aol.com) 2. 06:47 AM - Re: vor antenna (Noel Loveys) 3. 07:50 AM - Re: Low resistance measurement adapter. (paul wilson) 4. 07:50 AM - Re: vor antenna (BobsV35B@aol.com) 5. 08:24 AM - Re: Comm Antenna & SWR Reading (Robert L. Nuckolls, III) 6. 10:49 AM - Re: Low resistance measurement adapter. (Robert L. Nuckolls, III) 7. 01:30 PM - Re: Comm Antenna & SWR Reading (Noel Loveys) 8. 01:36 PM - Comm Antenna & SWR: More Information (Bob Falstad) 9. 02:26 PM - Re: Low resistance measurement adapter. (Keith Burris) 10. 05:15 PM - Re: Re: Low resistance measurement adapter. (Robert L. Nuckolls, III) 11. 06:36 PM - coax antenna cable length (Mike Welch) 12. 07:01 PM - Comm Antenna & SWR: Grounding the Ground Plane: Ref: Bob N's. Message 27 Posted on 1-25-11 (Bob Falstad) 13. 07:04 PM - lan tracer (bob noffs) 14. 07:18 PM - Re: Comm Antenna & SWR: More Information (Robert L. Nuckolls, III) 15. 07:19 PM - Re: coax antenna cable length (Robert L. Nuckolls, III) 16. 07:27 PM - Re: Comm Antenna & SWR: Grounding the Ground Plane: Ref: Bob N's. Message 27 Posted on 1-25-11 (Robert L. Nuckolls, III) 17. 07:48 PM - Re: Comm Antenna & SWR: More Information (BobsV35B@aol.com) 18. 08:08 PM - Re: Comm Antenna & SWR: More Information (Don) 19. 08:35 PM - Graphene (Speedy11@aol.com) 20. 08:47 PM - Re: lan tracer (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 04:00:35 AM PST US From: BobsV35B@aol.com Subject: Re: AeroElectric-List: vor antenna Good Morning Noel, I am sure you can get as many opinions as there are mechanics holding an IA, but I would just make log book entry which can be done by anyone holding an Airframe mechanic certificate. Strictly a Minor alteration in my opinion. Happy Skies, Old Bob A&P/IA Downers Grove, IL In a message dated 1/25/2011 10:15:30 P.M. Central Standard Time, noelloveys@yahoo.ca writes: Several early Pipers and Cessnas had the VOR antennas pointed forward. That is the way the Maintenance Manual required they be installed. I suppose to legally turn them around would require an STC. Noel From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Jared Yates Sent: January 25, 2011 6:16 PM Subject: Re: AeroElectric-List: vor antenna On an airplane with conventional landing gear, you might want to consider walkaround safety in your forward/aft decision. I had a friend with an old Piper and he just about poked his eye out one time on a set that was bent forward. On Tue, Jan 25, 2011 at 3:07 PM, Robert L. Nuckolls, III <_nuckolls.bob@aeroelectric.com_ (mailto:nuckolls.bob@aeroelectric.com) > wrote: <_nuckolls.bob@aeroelectric.com_ (mailto:nuckolls.bob@aeroelectric.com) > At 03:52 PM 1/25/2011, you wrote: I was once asked if it made any difference to the VOR whether the cats whiskers were sloping forward or rearward. What's your take? Mine was simply to follow the directions.. but in homebuilt planes you may have to write your own directions. Noel Good question. I've seen them both ways. Putting any kind of rake angle on them will have effects on radiation pattern, feed point impedance and aerodynamics. I suppose somebody had a reason for selecting one over the other but I doubt that it had to do with optimization in more than one of the three areas of investigation. From the performance perspective, it's almost sure to make no perceivable difference. Sometimes things are done just because that's the way we've been doing it for a long time . . . and nobody remembers why. Most folks would probably think they look sexier with a rearward rake . . . and indeed, that may have been the reason. Bob . . . , www.matronics.com/Navigator?AeroElectric-List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List ronics.com/" target="_blank">http://forums.matronics.com Matt Dralle, List Admin. ==== http://www.matronics.com/Navigator?AeroElectric-List http://forums.matronics.com http://www.matronics.com/contribution (http://www.matronics.com/Navigator?AeroElectric-List) (http://www.matronics.com/contribution) ________________________________ Message 2 _____________________________________ Time: 06:47:01 AM PST US From: "Noel Loveys" Subject: RE: AeroElectric-List: vor antenna Practically speaking I would just call the TC (Transport Canada) inspector and ask him about it. They can get uppity about things like that. But considering the speed of the aircraft he would probably authorize an entry. In the log entry I would also mention the discussion with the TC inspector. If the inspector was having a bad day he would insist on following the MM. Noel From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of BobsV35B@aol.com Sent: January 26, 2011 8:26 AM Subject: Re: AeroElectric-List: vor antenna Good Morning Noel, I am sure you can get as many opinions as there are mechanics holding an IA, but I would just make log book entry which can be done by anyone holding an Airframe mechanic certificate. Strictly a Minor alteration in my opinion. Happy Skies, Old Bob A&P/IA Downers Grove, IL In a message dated 1/25/2011 10:15:30 P.M. Central Standard Time, noelloveys@yahoo.ca writes: Several early Pipers and Cessnas had the VOR antennas pointed forward. That is the way the Maintenance Manual required they be installed. I suppose to legally turn them around would require an STC. Noel From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Jared Yates Sent: January 25, 2011 6:16 PM Subject: Re: AeroElectric-List: vor antenna On an airplane with conventional landing gear, you might want to consider walkaround safety in your forward/aft decision. I had a friend with an old Piper and he just about poked his eye out one time on a set that was bent forward. On Tue, Jan 25, 2011 at 3:07 PM, Robert L. Nuckolls, III wrote: At 03:52 PM 1/25/2011, you wrote: I was once asked if it made any difference to the VOR whether the cats whiskers were sloping forward or rearward. What's your take? Mine was simply to follow the directions.. but in homebuilt planes you may have to write your own directions. Noel Good question. I've seen them both ways. Putting any kind of rake angle on them will have effects on radiation pattern, feed point impedance and aerodynamics. I suppose somebody had a reason for selecting one over the other but I doubt that it had to do with optimization in more than one of the three areas of investigation. From the performance perspective, it's almost sure to make no perceivable difference. Sometimes things are done just because that's the way we've been doing it for a long time . . . and nobody remembers why. Most folks would probably think they look sexier with a rearward rake . . . and indeed, that may have been the reason. Bob . . . , www.matronics.com/Navigator?AeroElectric-List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List ronics.com/" target="_blank">http://forums.matronics.com Matt Dralle, List Admin. ==== http://www.matronics.com/Navigator?AeroElectric-List http://forums.matronics.com http://www.matronics.com/contribution =================================== List href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matro nics.com/Navigator?AeroElectric-List =================================== ms.matronics.com/">http://forums.matronics.com =================================== tp://www.matronics.com/contribution">http://www.matronics.com/contribution =================================== ________________________________ Message 3 _____________________________________ Time: 07:50:17 AM PST US From: paul wilson Subject: Re: AeroElectric-List: Low resistance measurement adapter. I would buy one from you before tackaling a build myself. Sign me up for one.. PaulW ======== At 04:18 PM 1/25/2011, you wrote: > > >At 05:37 PM 1/25/2011, you wrote: >>Bob, I remember this article well, which is why I asked if >>something is out there to buy. I seriously doubt a succesful build >>of your device considering my abilities. > > Nobody in your local acquaintance that could > help you? > >>Maybe you would consider a new product to sell us or even a kit? > > Hmmm . . . possibly a product. "Kits" tend to be more expensive > to gin-up and sell than completed products. I think something > like this would sell for $35 to $40. It would be interesting > to know if other folks on the List have an interest in having this > class of measurement capability. > > Maybe I could do a one-of-a-kind. It would take about > 30 minutes to built one. > > > Bob . . . > > ________________________________ Message 4 _____________________________________ Time: 07:50:17 AM PST US From: BobsV35B@aol.com Subject: Re: AeroElectric-List: vor antenna Good Morning Noel, I have absolutely NO knowledge as to how the Canadian rules are applied, but in the USA a lot of authority IS granted to a certificated maintenance person. He/she is supposed to make a decision as to whether some modification is a Major Alteration or a Minor Alteration. When the aircraft is next submitted for an annual inspection, the IA doing the inspection may or may not agree that the modification was a Minor one. If the IA thinks it is not, he can refuse to return the aircraft to service, but if the owner takes it to another IA who agrees that it is minor, the aircraft is returned to service. If some FAA inspector has occasion to examine the airplane, he/she may decide it was a Major Alteration, but that does not mean the airplane has been flown illegally between the time the first "A" mechanic signed it off and the time the FED says it is not legal. At that time, the FAA is to contact the parties and get it straightened out to everyone's satisfaction. Depending on how it is handled, it can be a very pleasant experience or a knock down, drag out, fight, but no one has done anything that he/she was not authorized to do. Personally. I NEVER ask an inspector what he thinks. I read the rules and make the decision based on my interpretation of what I read. If the FAA feels I am wrong, they are obligated to take action. What happens is that I am very careful as to what action I take and I try very hard to never do anything that I am not willing to support at a hearing Happy Skies, Old Bo Happy Skies, Old Bob Do Not Archive In a message dated 1/26/2011 8:48:05 A.M. Central Standard Time, noelloveys@yahoo.ca writes: Practically speaking I would just call the TC (Transport Canada) inspector and ask him about it. They can get uppity about things like that. But considering the speed of the aircraft he would probably authorize an entry. In the log entry I would also mention the discussion with the TC inspector. If the inspector was having a bad day he would insist on following the MM. Noel From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of BobsV35B@aol.com Sent: January 26, 2011 8:26 AM Subject: Re: AeroElectric-List: vor antenna Good Morning Noel, I am sure you can get as many opinions as there are mechanics holding an IA, but I would just make log book entry which can be done by anyone holding an Airframe mechanic certificate. Strictly a Minor alteration in my opinion. Happy Skies, Old Bob A&P/IA Downers Grove, IL In a message dated 1/25/2011 10:15:30 P.M. Central Standard Time, noelloveys@yahoo.ca writes: Several early Pipers and Cessnas had the VOR antennas pointed forward. That is the way the Maintenance Manual required they be installed. I suppose to legally turn them around would require an STC. Noel From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Jared Yates Sent: January 25, 2011 6:16 PM Subject: Re: AeroElectric-List: vor antenna On an airplane with conventional landing gear, you might want to consider walkaround safety in your forward/aft decision. I had a friend with an old Piper and he just about poked his eye out one time on a set that was bent forward. On Tue, Jan 25, 2011 at 3:07 PM, Robert L. Nuckolls, III <_nuckolls.bob@aeroelectric.com_ (mailto:nuckolls.bob@aeroelectric.com) > wrote: --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <_nuckolls.bob@aeroelectric.com_ (mailto:nuckolls.bob@aeroelectric.com) > At 03:52 PM 1/25/2011, you wrote: I was once asked if it made any difference to the VOR whether the cats whiskers were sloping forward or rearward. What's your take? Mine was simply to follow the directions.. but in homebuilt planes you may have to write your own directions. Noel Good question. I've seen them both ways. Putting any kind of rake angle on them will have effects on radiation pattern, feed point impedance and aerodynamics. I suppose somebody had a reason for selecting one over the other but I doubt that it had to do with optimization in more than one of the three areas of investigation. From the performance perspective, it's almost sure to make no perceivable difference. Sometimes things are done just because that's the way we've been doing it for a long time . . . and nobody remembers why. Most folks would probably think they look sexier with a rearward rake . . . and indeed, that may have been the reason. Bob . . . , ________________________________ Message 5 _____________________________________ Time: 08:24:22 AM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: Comm Antenna & SWR Reading At 10:51 PM 1/25/2011, you wrote: > >Bob: > >I think we are talking about slightly different things here. > >I suspect there is no direct connection between the braid of the coax >(ground) and the ground plane. Most of these antennas are designed to be >mounted on aluminium skins. I am thinking that the ground plane is totally >afloat and not connected in any way to the braid. Of course this is easy to >check by simply ringing between the ground plane and the exterior of the >BNC. The braid MUST come to a very low impedance connection to the ground plane else the coax becomes 'un-terminated'. In fact, the high SWR readings Bob cited may have been the result of poor contact between the antenna base and the ground plane. The ideal ground plane behaves as an infinite number of elements that might otherwise be a center fed dipole oriented in a plane at right angles to the antenna. Consider the dipole with coax center conductor to one element, shield to the other. Yeah, balanced antenna and unbalanced feedline . . . not the best we know how to do. Now bend the shield-side element 90 degrees to center- conductor element. Very lopsided and not quite so balanced antenna . . . with the 'bent' element NOT contributing to a useful radiation pattern. Start adding elements on the shield side. Once you get to 4 elements, 90 degrees apart, the current in each element is 1/16th and you have 4 resonant elements in parallel giving 1/4th feedpoint impedance compared to a single element. Tendency of the 'radials' to radiate is much suppressed and the lion's share of energy is conducted to the center-conductor element. Now increase the number of radials to 1 bazillion and you have a solid surface, not unlike the skin of an airplane . . . or the sheet of aluminum inside the composite shell of Bob's airplane. But for the antenna to perform at its best, the ideal radiation resistance of the ground plane is zero (lots in parallel). Further, the electrical connection from shield ground to ground plane is as close to zero ohms as we can make it. Bob . . . ________________________________ Message 6 _____________________________________ Time: 10:49:57 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Low resistance measurement adapter. At 10:27 AM 1/26/2011, you wrote: > >I would buy one from you before tackaling a build myself. Sign me up for one.. >PaulW Okay. I've figured out a way to package one with a minimum of time. I'll need to order some parts. The AEC9008-1 Low Ohms Test Adapter has been added to the catalog at: https://matronics.com/aeroelectric/Catalog/AECcatalog.html Interested individuals can place orders there. Bob . . . ________________________________ Message 7 _____________________________________ Time: 01:30:18 PM PST US From: "Noel Loveys" Subject: RE: AeroElectric-List: Comm Antenna & SWR Reading Now... I think I'm on your page! Most of the fancy high speed antennae I've seen have been made specifically made to mount on metal planes. Antennae for composite planes generally have the ground plane built in to them. The base of the antenna makes the connection for the ground plane while the mounting screws are simply that, a method to physically mount the antenna to the plane.... not necessarily to provide a path for the ground plane. BTW I do admire your explanations. Noel The braid MUST come to a very low impedance connection to the ground plane else the coax becomes 'un-terminated'. In fact, the high SWR readings Bob cited may have been the result of poor contact between the antenna base and the ground plane. The ideal ground plane behaves as an infinite number of elements that might otherwise be a center fed dipole oriented in a plane at right angles to the antenna. Consider the dipole with coax center conductor to one element, shield to the other. Yeah, balanced antenna and unbalanced feedline . . . not the best we know how to do. Now bend the shield-side element 90 degrees to center- conductor element. Very lopsided and not quite so balanced antenna . . . with the 'bent' element NOT contributing to a useful radiation pattern. Start adding elements on the shield side. Once you get to 4 elements, 90 degrees apart, the current in each element is 1/16th and you have 4 resonant elements in parallel giving 1/4th feedpoint impedance compared to a single element. Tendency of the 'radials' to radiate is much suppressed and the lion's share of energy is conducted to the center-conductor element. Now increase the number of radials to 1 bazillion and you have a solid surface, not unlike the skin of an airplane . . . or the sheet of aluminum inside the composite shell of Bob's airplane. But for the antenna to perform at its best, the ideal radiation resistance of the ground plane is zero (lots in parallel). Further, the electrical connection from shield ground to ground plane is as close to zero ohms as we can make it. Bob . . . ________________________________ Message 8 _____________________________________ Time: 01:36:31 PM PST US From: Bob Falstad Subject: AeroElectric-List: Comm Antenna & SWR: More Information Bob N., et al, I've been doing some reading re my antenna issue and here's what I've found so far (in no particular order). Cobham/Comant has some good information on installing their antennas. See Installation Guides (including PDF of AC43.13-2B): http://www.cobham.com/about-cobham/avionics-and-surveillance/about-us/satc om/fullerton/installation-guide.aspx FAQs http://www.cobham.com/about-cobham/avionics-and-surveillance/about-us/satc om/fullerton/faqs.aspx Data Sheet for the subject Comm Antenna that I'm using (Comant CI-122) http://www.cobham.com/media/9104/ci%20122%20data%20sheet.pdf Cobham/Comant's installation instructions follow AC43.13-2B fairly closely and, in fact, refer to that FAA Advisory Circular in several places. Additional detail about my ground plane installation. My ground plane isn't symmetrical (and, contrary to my earlier post, it is actually 24" x 34", not 24" x 36" -- I had cut 2" off the length so that it would fit in the space I had available). I also didn't mention that I cut two slots in the ground plane so that it would fit over a couple of supports for the floors in my baggage compartment. These slots are ~3" x 1/2" and are about 10" aft of the antenna base and about 4" either side of the fuselage centerline. Will these slots in the ground plane degrade the ground plane's performance? The ground plane is also primed with "rattle-can" self-etching primer. But as Bob N. supposed, I do have an access hole in the ground plane for the antenna BNC connector centered among the four 10-32 stainless machine screws in the antenna base. I used a washer stack to get as close as possible to the cored composite shell thickness and the hardware is clamped on the antenna base, through the non-cored fiberglass exterior skin, the washer stack and the ground plane. The ground plane metal is "bright" under the washers. Cobham/Comant endorses this approach (see FAQ #6 at http://www.cobham.com/about-cobham/avionics-and-surveillance/about-us/satc om/fullerton/faqs.aspx#171). Cobham/Comant says the resistance between the ground plane and the antenna connector should be 3 milliohms (see http://www.cobham.com/media/5051/compositeaircraftinstallation.pdf). My ohmmeter only reads to 0.1 Ohm and I can't measure lower than that without making up one of Bob N's four-wire ohmmeters. Antenna choice, revisit? Cobham/Comant isn't very positive about bent whip antennas for Comm 1. They say "Bent whips may not provide the best VSWR because of proximity to the ground plane (aircraft skin), which can cause reflections, plus they lack overall height. Remember, VHF antennas =93like=94 to be tall and straight for best operation." See FAQ #2. Other than the antenna selection issue itself, this reading leads me to three additional areas to investigate: ground plane symmetry, ground plane size, and antenna mounting location on ground plane. Re ground plane symmetry... AC43.13-2B, paragraph 310(b) on page 27 says that "...ground plane symmetry is critical." There is no reason or engineering data given but its a fairly direct statement. After re-running the tests with my 24" x 34" practice ground plane, I may cut it back to 24" x 24" to see what VSWR readings I get with that size. Re ground plane size... I understand that, in theory, the ideal ground plane is of infinite dimension. (For an aside, see quote below.) Bob N. says the practical ideal is a disc with a radius equal to one-quarter of the wavelength. An on-line calculator told me that the wavelength at 122.95 MHz is 8'. One fourth of that is 2'. But that means the idealized disc should have a diameter of 4'. My ground plane is only 24" wide -- half of what it should be. It isn't feasible to put a ground plane 4' wide in my plane -- most of it would have to curl up the sides of the fuselage which would defeat the purpose anyhow. Moreover, AC43.13-2B, paragraph 310(b), page 27, says most antennas require a ground plane size of approximately 24" x 24". Re antenna mounting location on ground plane... In addition to the issue of the symmetry of the ground plane itself, will it make a difference in VSWR if the antenna base is not mounted in the center of the ground plane. As I mentioned in my earlier post, I mounted the base about 1/3 of the distance along the long axis so that the entire bent whip would be "covered" by the ground plane. But if, electrically, the bent whip really behaves like the straight piece of 12 AWG wire Bob N. used in his experiment, then that seems to indicate that the antenna base needs to be installed in the center of the ground plane, whether the ground plane is square or rectangular. Next steps... I'm finishing up the final terminations on my feed lines and will jury-rig an external ground plane in order to re-do the tests outside the airplane as Bob N. suggested. I hope to have the new test data to you in the next couple of days. Bonus data point re VOR Antenna installation direction... Cobham/Comant says the dipoles should be pointed forward. See http://www.cobham.com/about-cobham/avionics-and-surveillance/about-us/satc om/fullerton/faqs.aspx#171 Do VOR/GS V-Dipoles such as the CI 158C need to be =93pointed=94 forward or aft ? For best results, the radiating elements should be directed forward, as the emitted pattern needs to =93see=94 forward and downward. However, some aircraft owners believe they provide a better appearance if the radiators are pointed aft. If mounted in this manner, the installer should flight check for proper antenna performance. (I installed my pointing aft because it looks better. Now I'll have to pay extra attention on the flight check.) Best regards, Bob Falstad GlaStar N248BF "In theory, there is no difference between theory and practice. In practice, there is." (I've heard this attributed to various people, most often Yogi Berra.) ________________________________ Message 9 _____________________________________ Time: 02:26:55 PM PST US From: "Keith Burris" Subject: AeroElectric-List: Re: Low resistance measurement adapter. Bob; Id be interested in the device. -- Keith ________________________________ Message 10 ____________________________________ Time: 05:15:25 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Low resistance measurement adapter. At 05:20 PM 1/26/2011, you wrote: >Bob; >I'd be interested in the device. I have orders for several. You can join them at: https://matronics.com/aeroelectric/Catalog/AECcatalog.html Bob . . . ________________________________ Message 11 ____________________________________ Time: 06:36:46 PM PST US From: Mike Welch Subject: AeroElectric-List: coax antenna cable length Guys=2C I have seen it suggested that when cutting off an antenna cable for your com radio=2C nav radio=2C etc.=2C that you are supposed to cut the cable at EVEN multiples of one length of a dipole mast. In the example of a com radio=2C one article states the dipole length of a com radio to be 20". Therefore=2C you should double this=2C and use this new length to calculate your final minimum cable length. Like this=3B dipole = 20"=2C so our increment would be 40". Now=2C beginning at the back of the radio (not at a junction of a pigtail)=2C start counting off 40" increments until we have enough cable to comfortably reach the actual antenna. Meaning=3B only cut the cable at 40"=2C 80"=2C 120"=2C 160"=2C 200"=2C etc. If=2C after we've done an excellent routing of the cable=2C we find our antenna is not located at a 40" increment=2C then we should proceed to the next full length of our 40" increment prior to cutting the cable. Here's my question=3B I read from a prominent=2C nationally known=2C avionics guru that this is not all that necessary. If I recall correctly =2C he said he has done SWR tests=2C and the cable length (cut off at even multiples) had little effect on the antennas performance. In other words=2C it didn't really matter what the cable length was=2C i.e..=2C 180" or 205"=2C etc. If I'm a little fuzzy on my facts here=2C it's because this information is from several years ago. But=2C after all these years=2C I really would like to now the facts!! Is it really all that critical what the cut-off measurement is for a coax cable for aircraft radios? Thanks=2C Mike Welch ________________________________ Message 12 ____________________________________ Time: 07:01:19 PM PST US From: Bob Falstad Subject: AeroElectric-List: Comm Antenna & SWR: Grounding the Ground Plane: Ref: Bob N's. Message 27 Posted on 1-25-11 Bob N., et al, Based on his reading of Figure 3-4 on page 28 of AC43.13-2B, my Ham/EE/PE buddy asked me to check the resistance between the ground plane and the ground system in my plane. (And yes, as you correctly surmised, I'm using a B&C "forest of tabs" on the firewall for my grounding system supplemented with your 37-pin Dsub ground bus for avionics grounds mounted next to it.) As expected, there was a complete open between my ground plane and the grounding system in the airplane. This is consistent with your comments in the message referenced above. But when, for example, a comm antenna is mounted on top of the wing on a Cessna, I presume it is electrically bonded to the wing which acts as the ground plane. But isn't the wing also part of the ground system for the airplane itself? With a coax connector attached to the antenna isn't there now two ground paths from the antenna to the radio chassis in its mounting rack? Does this create a ground loop and if so, are its effects positive, benign, or negative? Or is the ground through the coax between the antenna and the radio isolated in the radio chassis so the loop isn't completed? In thinking about my setup (if I had an-all metal airplane), it seems like the loop would be completed since the BNC connector at the radio end of the feed line connects to another BNC connector that is mounted in the back plane of the radio (Garmin 430W) chassis and it appears to me that the pass-through BNC connector in the chassis back plane isn't insulated from the radio chassis itself. Your thought and comments? Best regards, Bob Falstad GlaStar N248BF ________________________________ Message 13 ____________________________________ Time: 07:04:14 PM PST US Subject: AeroElectric-List: lan tracer From: bob noffs hi all, anyone have any experience with a wire tracer that they can recommend one? under $ 60 i hope. bob noffs ________________________________ Message 14 ____________________________________ Time: 07:18:18 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Comm Antenna & SWR: More Information Additional detail about my ground plane installation. My ground plane isn't symmetrical (and, contrary to my earlier post, it is actually 24" x 34", not 24" x 36" -- I had cut 2" off the length so that it would fit in the space I had available). I also didn't mention that I cut two slots in the ground plane so that it would fit over a couple of supports for the floors in my baggage compartment. These slots are ~3" x 1/2" and are about 10" aft of the antenna base and about 4" either side of the fuselage centerline. Will these slots in the ground plane degrade the ground plane's performance? Not much . . . if any. Let's consider the way a ground plane works. In an earlier post I explained how the sum total of 4 'prefect' radials routed 80% plus of energy delivered to the end of the coax to be delivered to the antenna. Now, if you draw say 100 equally spaced lines from the antenna location on your ground plane out to the edge, we can see that the minimum 'radial' length is on the order of 12". No single 12" radial is very useful . . . but there's a lot of them. The longest radial goes out to 2 or more corners. They might be as short as 20' but perhaps longer if the antenna is not directly centered on the sheet. [] Obviously, the ground plane is not "ideal". But then lots of satisfactory antenna installations were 'grounded' to small plates welded to the structure of a rag-n-tube airplane. Terrible radials. Your ground plane sheet is blessed with a few pretty good radials and lots of not so good but the SUM TOTAL of their effects at the base of the antenna is substantial . . . and probably quite adequate. With respect to 'measuring' resistance between the antenna base and the airframe, know that very few installations get such treatment. Practiced installers know that certain processes ALWAYS yield good bonding. Further, those same processes yield joints with good longevity in service. If your coax is good, the connectors are properly installed AND you apply reliable processes for getting high pressure connection between antenna base and ground plane, an micro-ohmmeter test will be quite predictable and therefore redundant. Antenna choice, revisit? Cobham/Comant isn't very positive about bent whip antennas for Comm 1. They say "Bent whips may not provide the best VSWR because of proximity to the ground plane (aircraft skin), which can cause reflections, plus they lack overall height. Remember, VHF antennas "like" to be tall and straight for best operation." See FAQ #2. Not true. It's the current flowing in about the bottom 20% of the antenna element that controls most of an antenna's performance. In fact, it's common practice to mechanically shorten an antenna with "capacity hats" that act strongly in low current, high voltage portion of the antenna element. Bending the top of the antenna horizontal has little effect on radiation pattern but will lower the frequency of resonance. Other than the antenna selection issue itself, this reading leads me to three additional areas to investigate: ground plane symmetry, ground plane size, and antenna mounting location on ground plane. Go for the bonding . . . get that right and you're 98% done. Re ground plane symmetry... AC43.13-2B, paragraph 310(b) on page 27 says that "...ground plane symmetry is critical." There is no reason or engineering data given but its a fairly direct statement. After re-running the tests with my 24" x 34" practice ground plane, I may cut it back to 24" x 24" to see what VSWR readings I get with that size. Please don't do this. AC43-13 was NOT crafted by skilled practitioners of the arts or science of building airplanes . . . That's another story. See page 2 of http://www.aeroelectric.com/articles/Getting_Started.pdf Re ground plane size... I understand that, in theory, the ideal ground plane is of infinite dimension. That's the 'perfect'. . . the 'ideal' is more practical (For an aside, see quote below.) Bob N. says the practical ideal is a disc with a radius equal to one-quarter of the wavelength. An on-line calculator told me that the wavelength at 122.95 MHz is 8'. One fourth of that is 2'. But that means the idealized disc should have a diameter of 4'. My ground plane is only 24" wide -- half of what it should be. It isn't feasible to put a ground plane 4' wide in my plane -- most of it would have to curl up the sides of the fuselage which would defeat the purpose anyhow. Moreover, AC43.13-2B, paragraph 310(b), page 27, says most antennas require a ground plane size of approximately 24" x 24". Which supports the assertions I made earlier about AC43-13 . . . 24 x 24 is a practical 'ideal' ground plane for 174 Mhz given that the 4 best radials are only 17" long. Re antenna mounting location on ground plane... In addition to the issue of the symmetry of the ground plane itself, will it make a difference in VSWR if the antenna base is not mounted in the center of the ground plane. As I mentioned in my earlier post, I mounted the base about 1/3 of the distance along the long axis so that the entire bent whip would be "covered" by the ground plane. But if, electrically, the bent whip really behaves like the straight piece of 12 AWG wire Bob N. used in his experiment, then that seems to indicate that the antenna base needs to be installed in the center of the ground plane, whether the ground plane is square or rectangular. Next steps... I'm finishing up the final terminations on my feed lines and will jury-rig an external ground plane in order to re-do the tests outside the airplane as Bob N. suggested. I hope to have the new test data to you in the next couple of days. A good experiment . . . if you're really curious and want to do it. Bob . . . ________________________________ Message 15 ____________________________________ Time: 07:19:35 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: coax antenna cable length At 09:32 PM 1/26/2011, you wrote: >Guys, > > I have seen it suggested that when cutting off an antenna cable >for your com radio, nav radio, etc., that you are supposed to cut >the cable at EVEN multiples of one length of a dipole mast. > > Is it really all that critical what the cut-off measurement is for a coax >cable for aircraft radios? No. Bob . . . ________________________________ Message 16 ____________________________________ Time: 07:27:02 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Comm Antenna & SWR: Grounding the Ground Plane: Ref: Bob N's. Message 27 Posted on 1-25-11 At 09:56 PM 1/26/2011, you wrote: Bob N., et al, Based on his reading of Figure 3-4 on page 28 of AC43.13-2B, my Ham/EE/PE buddy asked me to check the resistance between the ground plane and the ground system in my plane. (And yes, as you correctly surmised, I'm using a B&C "forest of tabs" on the firewall for my grounding system supplemented with your 37-pin Dsub ground bus for avionics grounds mounted next to it.) Check the chapter on grounding in the 'Connection. Also check the antennas and feedline chapter. DC power ground systems and antenna ground planes have no functional relationship to each other. It just so happens that they are sort of one chunk of metal when your talking about a metal airplane. But if the airplane is plastic, all commonality ceases. As expected, there was a complete open between my ground plane and the grounding system in the airplane. This is consistent with your comments in the message referenced above. There are gazillions of antennas on tops of poles that look like this: Emacs! None are even associated with the DC power system of the radio at the other end of coax feed line. But when, for example, a comm antenna is mounted on top of the wing on a Cessna, I presume it is electrically bonded to the wing which acts as the ground plane. But isn't the wing also part of the ground system for the airplane itself? With a coax connector attached to the antenna isn't there now two ground paths from the antenna to the radio chassis in its mounting rack? Does this create a ground loop and if so, are its effects positive, benign, or negative? Or is the ground through the coax between the antenna and the radio isolated in the radio chassis so the loop isn't completed? In thinking about my setup (if I had an-all metal airplane), it seems like the loop would be completed since the BNC connector at the radio end of the feed line connects to another BNC connector that is mounted in the back plane of the radio (Garmin 430W) chassis and it appears to me that the pass-through BNC connector in the chassis back plane isn't insulated from the radio chassis itself. Your getting the investigation wrapped around the axles of irrelevant data. Get your ground plane bonding taken care of and you're good to go. Bob . . . ________________________________ Message 17 ____________________________________ Time: 07:48:28 PM PST US From: BobsV35B@aol.com Subject: Re: AeroElectric-List: Comm Antenna & SWR: More Information Good Evening All, This discussion about ground planes has forced me to send another one of my way off subject messages! Some of you may be aware of the speed modifications that Mike Smith was selling for Bonanzas a few years ago. While Bonanzas are certainly NOT homebuilt aircraft, Mike's work was very much in the realm of what homebuilders do. He guaranteed a speed increase of at least ten knots on any Bonanza that used his full set of speed kits. In his quest for speed, he took EVERYTHING off the top of the fuselage and as much off the belly as humanly possible. He even installed a VHF communication antenna in a fiberglass tail cone. It was horizontally oriented rather than vertical and the ground plane was no more than six inches by eight inches. Did it work? Some folks found that it was a perfectly usable solution and are still using it regularly. Others have either eliminated it or added another stock antenna on the belly. Personally, I have never flown a Bonanza that was equipped with the tail cone antenna, but I have personally spoken to a pilot who has flown his that way in heavy IFR operations for over twenty years. Just how good do antennas really NEED to be? Mike also was a big exponent of using a set of VHF Navigation blades mounted as far back on the Bonanza fuselage as possible. The manufacturer of the antennas said they were way too close to the tail feathers to work properly. I have personally mounted several blade antennas in that position and they have all worked very well. Just some data for further thought. Happy Skies, Old Bob Downers Grove, IL LL22 Stearman 3977A Do Not Archive In a message dated 1/26/2011 9:19:32 P.M. Central Standard Time, nuckolls.bob@aeroelectric.com writes: Additional detail about my ground plane installation. My ground plane isn't symmetrical (and, contrary to my earlier post, it is actually 24" x 34", not 24" x 36" -- I had cut 2" off the length so that it would fit in the space I had available). I also didn't mention that I cut two slots in the ground plane so that it would fit over a couple of supports for the floors in my baggage compartment. These slots are ~3" x 1/2" and are about 10" aft of the antenna base and about 4" either side of the fuselage centerline. Will these slots in the ground plane degrade the ground plane's performance? ________________________________ Message 18 ____________________________________ Time: 08:08:43 PM PST US From: "Don" Subject: RE: AeroElectric-List: Comm Antenna & SWR: More Information One more antenna that is not done right and still works fine. The ELT on many RV's is horizontal and inside the tail cone fairing. Or in the baggage area with only the top few inches not close to metal. Neither of these install techniques have good ground planes nor the correct orientation but they work with both the 121.5 and the 406 versions of ELT From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of BobsV35B@aol.com Sent: Wednesday, January 26, 2011 7:44 PM Subject: Re: AeroElectric-List: Comm Antenna & SWR: More Information Good Evening All, This discussion about ground planes has forced me to send another one of my way off subject messages! Some of you may be aware of the speed modifications that Mike Smith was selling for Bonanzas a few years ago. While Bonanzas are certainly NOT homebuilt aircraft, Mike's work was very much in the realm of what homebuilders do. He guaranteed a speed increase of at least ten knots on any Bonanza that used his full set of speed kits. In his quest for speed, he took EVERYTHING off the top of the fuselage and as much off the belly as humanly possible. He even installed a VHF communication antenna in a fiberglass tail cone. It was horizontally oriented rather than vertical and the ground plane was no more than six inches by eight inches. Did it work? Some folks found that it was a perfectly usable solution and are still using it regularly. Others have either eliminated it or added another stock antenna on the belly. Personally, I have never flown a Bonanza that was equipped with the tail cone antenna, but I have personally spoken to a pilot who has flown his that way in heavy IFR operations for over twenty years. Just how good do antennas really NEED to be? Mike also was a big exponent of using a set of VHF Navigation blades mounted as far back on the Bonanza fuselage as possible. The manufacturer of the antennas said they were way too close to the tail feathers to work properly. I have personally mounted several blade antennas in that position and they have all worked very well. Just some data for further thought. Happy Skies, Old Bob Downers Grove, IL LL22 Stearman 3977A Do Not Archive In a message dated 1/26/2011 9:19:32 P.M. Central Standard Time, nuckolls.bob@aeroelectric.com writes: Additional detail about my ground plane installation. My ground plane isn't symmetrical (and, contrary to my earlier post, it is actually 24" x 34", not 24" x 36" -- I had cut 2" off the length so that it would fit in the space I had available). I also didn't mention that I cut two slots in the ground plane so that it would fit over a couple of supports for the floors in my baggage compartment. These slots are ~3" x 1/2" and are about 10" aft of the antenna base and about 4" either side of the fuselage centerline. Will these slots in the ground plane degrade the ground plane's performance? ________________________________ Message 19 ____________________________________ Time: 08:35:13 PM PST US From: Speedy11@aol.com Subject: AeroElectric-List: Graphene Bob, I'm sure you're familiar with this, but this blog is the first I've heard of it. More info is on the CAFE Blog at _http://blog.cafefoundation.org/?p=2439 _ (http://blog.cafefoundation.org/?p=2439) . Stan Sutterfield Thin, Light, Strong, and Energy Dense by Dean Sigler on 01/07/2011 _2010=99s Nobel Prize in Physics _ (http://nobelprize.org/nobel_prizes/physics/laureates/2010/press.html) wen t to Andre Geim and Konstantin Novoselov, who extracted graphene from a piece of graphite when they stuck a piece of adhesive tape to it and peeled away a single atom-thick layer of the thinnest, strongest material in the world. The Nobel Prize web site explains other remarkable properties of this new material. =9CAs a conductor of electricity it performs as well as copper. As a conductor of heat it outperforms all other known materials. It is almost completely transparent, yet so dense that not even helium, the smallest ga s atom, can pass through it. Carbon, the basis of all known life on earth, has surprised us once again.=9D When mixed into plastics, graphene can turn them into conductors of electricity while making them more heat resistant and mechanically robust. Over 28,000 square feet per gram for a single layer of the material =93 or about the size of a football field ________________________________ Message 20 ____________________________________ Time: 08:47:03 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: lan tracer At 10:01 PM 1/26/2011, you wrote: >hi all, > anyone have any experience with a wire tracer that they can > recommend one? under $ 60 i hope. > bob noffs How about these? http://tinyurl.com/49bj2pa http://tinyurl.com/4hnlvvh Bob . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.