---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 01/28/11: 20 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:03 AM - ELT antenna performance (Robert L. Nuckolls, III) 2. 08:42 AM - Unfortunate Antenna Instructions (Robert L. Nuckolls, III) 3. 08:42 AM - Re: lan tracer (jonlaury) 4. 08:52 AM - Re: ELT antenna performance (Richard Tasker) 5. 10:21 AM - Re: ELT antenna performance (Robert L. Nuckolls, III) 6. 10:41 AM - Re: Re: lan tracer (Bob McCallum) 7. 11:58 AM - Re: Comm Antenna & SWR: More Information (Noel Loveys) 8. 12:22 PM - Re: coax antenna cable length (Noel Loveys) 9. 12:30 PM - Re: ELT antenna performance (kuffel@cyberport.net) 10. 12:38 PM - Re: Comm Antenna & SWR: More Information (Noel Loveys) 11. 12:57 PM - Re: Comm Antenna & SWR: More Information (Noel Loveys) 12. 03:07 PM - Re: Comm Antenna & SWR: More Information (Robert L. Nuckolls, III) 13. 04:28 PM - Re: ELT antenna performance (Noel Loveys) 14. 04:28 PM - Re: ELT antenna performance (Noel Loveys) 15. 04:56 PM - Re: ELT antenna performance (Mike Welch) 16. 06:51 PM - Re: Graphene (Bill Watson) 17. 09:58 PM - BNC connectors (John F. Herminghaus) 18. 10:20 PM - Re: BNC connectors (Robert L. Nuckolls, III) 19. 11:39 PM - OT-potting with RTV silicone (rayj) 20. 11:39 PM - Re: BNC connectors (John F. Herminghaus) ________________________________ Message 1 _____________________________________ Time: 07:03:28 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: ELT antenna performance At 11:54 PM 1/27/2011, you wrote: >Bob and all, >During an emergency landing too many aircraft go over on their backs. or suffer severe deformation/disassembly > I suspect that the back contact and sliding in too many instances > scrapes off or otherwise damages antenna like the ELT typically use. which is why the preferred location for ELT antenna is just forward of the vertical fin. Studies of wreckage remains determined that this was the lowest risk location for the antenna . . . unfortunately, "lowest" is not a nice number near zero. > > From that situation, I have wondered about a design concept that > would allow the ELT to feed either two or one antennas with enough > radiation to get someone's attention. The thought goes something > like this. Have an antenna both top and bottom of the fuselage > region. Hoping that one survives the impact and will radiate the ELT signal. Having the system upside down is not as deleterious as one might imagine. UHF behaves quite a bit differently than VHF. When I first got into electronics as a profession, I was working for a two-way radio company in Wichita. We serviced a few systems in the 72 mHz band but most were in the vicinity of 150 mHz and a few were up about 450. This was all vacuum tube stuff. The 450 mHz equipment was at the upper fringe of what was practical. It was harder to develop power, losses in feedlines was higher, keeping receiver sensitivity to less than 1 microvolt was more demanding. All-in-all, higher cost of ownership. You'd think that customers would shy away from this equipment. On the contrary. Antennas were more efficient. Terrestrial noise was a small influence. Signals behaved much better in the confines of tall buildings. The cab companies wouldn't have anything different. The police wanted it but the FCC decreed that public services will conduct business in the 150 mHz band. 150 mHz was subject to much more multi- path nulls and noise. 121.5 mHz was picked for the first ELTs because it was a frequency already serviced by aviation communication services. Same with 243 albeit military. The idea was that folks having nothing better to do on long trips might monitor the emergency frequencies and report any contacts. Heaven knew that the satellite location technology was EXCEEDINGLY crude. Location accuracy was poor (100 square miles or more), it took three or more satellite passes to get that good (meaning many hours after first contact) and that assumed that they could sort out the distressed aircraft from several dozen false triggers that every satellite could hear within it's line-of-sight cone. Combine this with the relatively poor performance of VHF propagation in general and you begin to see why the system was doomed to poor performance from the beginning. 6% find-rates was considered great performance by some. Then came solid state UHF electronics where communications at 2,000 Mhz was no big deal. Add ship's i.d. GPS location features to the ELT's transmitted signals and that 6% number took a big jump. They have a better chance of sorting out your distress from other people's false alarms.Haven't seen the latest figures but I'll bet there are no more than 25% of found wrecks where attributed to ELT performance where rescue outcomes were good . . . I'd be delighted to be wrong. Getting back to upside-down wrecks. The UHF propagation performance is so much better than the old 121.5/243 junk that antenna orientation and shadowing is much less critical. I've not been privy to detailed discussion on ELT systems. But given what I know of UHF propagation behavior, if the system is not physically disabled, the system is going to perform about as well as expected irrespective of wreckage configuration. But the real bottom line is, what is the return-on-investment for having installed an ELT? How many wrecks in the history of all aviation crashes would have had a better outcome for the occupants had the guys in white coats with stretchers arrived say within two hours of the crash? In other words, what percentage of all events resulted in occupants surviving for hours to days but unable to fend for themselves due to non-lethal injury or simple lack of transport? The ELT makes a lot of sense for over-water flight where there is higher probability of non-lethal landing and perhaps days of post crash survival on a float. But pile an airplane into a mountain or even average terrain at night and the ELT becomes more of a whistle in the dark. If you really want the folks in white coats to show up fast, make sure you've added the GPS position data option. At least they KNOW where you are. Now the problem is to get to you with what ever resources are available for the task. Those resources are dwindling . . . but that's another issue. > >Any thoughts about a design that could "reasonably" match and feed >either two (if both survive) or the remaining antenna.... Sure. You could install rugged, flush mounted slot antennas on top and bottom of the tail. Use a power divider to feed both antennas. This would demand some analysis and perhaps demonstrated experiments to determine it was really that much better. I suspect that the numbers guys would find that going to dual, robust antennas would double installation costs while making that 25% go up to 26.2% or some such. I'm pretty sure it's been explored. The ELT guys would be DELIGHTED to have dual robust antennas added to the mandate for installing such systems. If it made any sense at all, they'd be doing it. Bob . . . ________________________________ Message 2 _____________________________________ Time: 08:42:19 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Unfortunate Antenna Instructions I've been given a copy of S-H antenna installation instructions for review. I have the following observations to share with members of the List. The article has been posted at: http://tinyurl.com/4cwq4yy ADJUSTING the ANTENNA CABLE LENGTH The process described under this title is a salute to an old hangar myth that antenna system performance can be improved by cutting coax feed lines to (1) multiples of half-wavelengths or (2) maximize measured field strength on some particular frequency. As we discussed last week, the ONLY time that observable effects are affected by length of the transmission line is when the SWR on that line is high. The most profound effects for fiddling with length will be noted when SWR is a lot higher than what is traditionally accepted as optimum performance. 3:1 or better. This myth has roots that go back a long way in aviation history. I recall similar discussions back in the 60's. I would challenge the publisher of any such document to search any engineering text and/or any ARRL publication on amateur built antennas. They will not find any similar suggestion anywhere. The adequately designed antenna presents a load to the feedline that has no observable, deleterious effects on system performance. An interesting feature of the S-H suggestion is that even if there WERE a valid reason for crafting an even- multiples-half-wave transmission line, the coax cuts would NOT be multiples of the free-space wavelength used to design the antenna. Propagation velocity of energy down a transmission line is SLOWER than in free space. Depending on how the coax is made, the VELOCITY FACTOR will be some number near .66 This means that for a 1/4-wave, 24" antenna element length a 1/2 wave in coax would NOT be 48" but 48 x .66 or 31.5 inches. Unfortunately, the idea published in this document is not only non-sense, it is poorly implemented based on bad science. INSTALLING BNC CONNECTORS Finally, the tri-axial cable called out was designed for use in systems were special connectors maintain SEPARATED shield integrity throughout the system. VERY expensive and rare connectors. On the other hand, RG-58 has been handily replaced throughout the TC aircraft world with RG-400 or RG142 which are DOUBLE LAYER bi-axial feedlines that accept the standard RG-58 connectors with no fabrication acrobatics. It's unfortunate that this publication has been circulated to S-H customers for 14 years. It has no doubt generated a lot of unnecessary no-value added taxation of their customer's time, talents and resources. Bob . . . ________________________________ Message 3 _____________________________________ Time: 08:42:19 AM PST US Subject: AeroElectric-List: Re: lan tracer From: "jonlaury" Try www.allelectroincs.com , cat#28, $12 Read this topic online here: http://forums.matronics.com/viewtopic.php?p=328832#328832 ________________________________ Message 4 _____________________________________ Time: 08:52:51 AM PST US From: Richard Tasker Subject: Re: AeroElectric-List: ELT antenna performance Hey Bob, not to pick nits , but you are the example here after all... ;-) mHz - millihertz MHz - megahertz Dick Tasker Robert L. Nuckolls, III wrote: > When I first got into electronics as a profession, > I was working for a two-way radio company in Wichita. > We serviced a few systems in the 72 mHz band but > most were in the vicinity of 150 mHz and a few > were up about 450. > > This was all vacuum tube stuff. The 450 mHz > equipment was at the upper fringe of what > was practical. It was harder to develop power, > losses in feedlines was higher, keeping > receiver sensitivity to less than 1 microvolt > was more demanding. All-in-all, higher > cost of ownership. > > You'd think that customers would shy away from > this equipment. On the contrary. Antennas were > more efficient. Terrestrial noise was a small > influence. Signals behaved much better in the > confines of tall buildings. The cab companies > wouldn't have anything different. The police > wanted it but the FCC decreed that public > services will conduct business in the 150 mHz > band. 150 mHz was subject to much more multi- > path nulls and noise. > > 121.5 mHz was picked for the first ELTs > because it was a frequency already serviced > by aviation communication services. Same > with 243 albeit military. ________________________________ Message 5 _____________________________________ Time: 10:21:54 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: ELT antenna performance At 11:15 AM 1/28/2011, you wrote: >Hey Bob, not to pick nits , but you are the example here after all... ;-) > >mHz - millihertz > >MHz - megahertz > >Dick Tasker You're quite correct. Unfortunately, when trying to bang out a timely but extensive reply, I don't have the luxury of coming back to edit it tomorrow to attempt a 99% clean posting. When I go back and read my past postings, it's not unusual to get whacked by spelling/semantics issues. I'll just have to beg the Lists indulgence. That doesn't mean I don't want to hear from folks when I've stubbed my toe. Just be forewarned that in spite of your most honorable efforts, my head will probably continue to run out in front of fingers on the keyboard. Thanks for the heads-up! Bob . . . ________________________________ Message 6 _____________________________________ Time: 10:41:23 AM PST US From: Bob McCallum Subject: RE: AeroElectric-List: Re: lan tracer John; Check the link you posted. It leads to a website phishing for cell phone numbers. I suspect that when you wrote "allelectroincs" you might have meant "allelectronics", but catalogue #28 does not appear to exist on their website and all of their part numbers appear to consist of an alpha prefix followed by a dash and then a number. There do not appear to be any numbers fitting your posting. Please clarify. Bob McC > -----Original Message----- > From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list- > server@matronics.com] On Behalf Of jonlaury > Sent: Friday, January 28, 2011 11:39 AM > To: aeroelectric-list@matronics.com > Subject: AeroElectric-List: Re: lan tracer > > > Try www.allelectroincs.com , cat#28, $12 > > > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=328832#328832 > > > > > > > > _- > ==================================================== > ====== > _- > ==================================================== > ====== > _- > ==================================================== > ====== > _- > ==================================================== > ====== > > ________________________________ Message 7 _____________________________________ Time: 11:58:55 AM PST US From: "Noel Loveys" Subject: RE: AeroElectric-List: Comm Antenna & SWR: More Information The stick in the tail reminds me of when I was a kid my dad had shares in a company which carried out the seal hunt using a spotter plane and a helicopter. Daily reports from the front (the harvesting area) were sent form the spotter plane via HF. The plane had a trailing =9CWet Noodle=9D antenna which could not be heard when he was flying toward our town.. If the plane flew a direction 90 deg to that we copied him perfectly. With a com radio it is important that everyone be able to hear you and the reverse too... You must be able to hear everyone else in your vicinity... That is hard to do with a horizontally p[olarized antenna at those frequencies. As for telling people they can=99t do that... That=99s not my job but I sure don=99t mind telling them of some of the problems they probably will have with a specific set up. Noel From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of BobsV35B@aol.com Sent: January 27, 2011 9:53 PM Subject: Re: AeroElectric-List: Comm Antenna & SWR: More Information Good Evening Noel, I don't think anyone will disagree with what you say, but the point is that a lot of good competent and concientuous folks have found that the crummy location does work acceptably. You and I can agree it is not good, but if it works for others, are we supposed to tell them it is not allowed? As 'Lectric Bob has said, chances are a wet noodle will work most of the time. While I know folks who are still using the stick in the tail cone, I know more who have given up on it and gone to a more conventional antenna. As Always.It All Depends! Do Not Archive Happy Skies, Old Bob In a message dated 1/27/2011 6:27:12 P.M. Central Standard Time, noelloveys@yahoo.ca writes: The important thing with com antennas is good omnidirectional ( all directions ) coverage. A horizontally polarized antenna in a tailcone, outside of having too small a ground plane, will have a dead area in front of the plane and another one behind it. I can=99t see how this can be considered good for airplanes heading into or away from a control zone. Many large aircraft actually have antennae above and below the fuselage to allow communication with other aircraft as well as ground. Noel From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of BobsV35B@aol.com Sent: January 27, 2011 12:14 AM 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? 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. matronics.com/Navigator?AeroElectric-List ms.matronics.com/">http://forums.matronics.com tp://www.matronics.com/contribution">http://www.matronics.com/contributio n ________________________________ Message 8 _____________________________________ Time: 12:22:58 PM PST US From: "Noel Loveys" Subject: RE: AeroElectric-List: coax antenna cable length What I was getting at was not to reroute the wire or coil it up to take care of excess. Cut it off. I think you agree as I agree the longer coax appears to have a better swr but in fact it has greater line losses. Certainly I agree that no one should ever add length to the feed wire to achieve a mach. Noel -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: January 27, 2011 10:00 PM Subject: RE: AeroElectric-List: coax antenna cable length At 06:27 PM 1/27/2011, you wrote: >That's the first I've heard of anything like this. As Bob has said, >the longer the feed cable (coax) the closer the match to the radio >will be to 50 Ohms but you will then also have to contend with line losses. > >The question than has to be what to do with the access cable? If >you coil it up you can be opening a whole new can or >worms. Re-routing it can also cause problems. Best to decide on >the best possible routing and install leaving just enough cable for drip loops. I did not intended proffer the idea that one would purposely ADD coax to a feedline for the purpose of reducing SWR. It is because longer feedlines ADD losses that the SWR appears to improve while in fact, the effects of real SWR are being masked by those losses. It was an observation of fact, not a recommendation. Bob . . . ________________________________ Message 9 _____________________________________ Time: 12:30:08 PM PST US From: "kuffel@cyberport.net" Subject: Re: AeroElectric-List: ELT antenna performance After my first couple hundred aircraft searches up in Alaska, and only two crashes myself, I've come to the strong opinion a terrible ELT antenna inside the structure works infinitely better than any exterior one removed in the crash. Suggest builders consider a tailcone location for fiberglass aircraft or somewhere, anywhere, in the cockpit for metal ones. It appears the 406 MHz ELTs will require one to use the manufacturer's antenna to be legal so we probably can no longer roll our own ELT dipoles or whips. But using a simple ground plane in a glass tail or any handy metal surface in the cockpit will do the job. Don't worry too much about "seeing the sky". Orientation doesn't matter. If you really need ELT operation you are unlikely to be upright anyway. Tom Kuffel ________________________________ Message 10 ____________________________________ Time: 12:38:59 PM PST US From: "Noel Loveys" Subject: RE: AeroElectric-List: Comm Antenna & SWR: More Information ???? The VOR antenna whiskers are horizontally polarized dipole with major lobes fore and aft with nulls off to the sides. Further, dipole antennas require no ground plane. VOR is not a transmitting antenna. The VOR transmitters are on the ground and are also horizontally polarized. The receive lobes of the antennae are part insignificant as aircraft do not approach the VOR sideways. No such "null" exists fore and aft. Experience as well as radio theory tells me is sure does exist on the tip of horizontally polarized signals. >Many large aircraft actually have antennae above and below the >fuselage to allow communication with other aircraft as well as ground. ???? Antenna placement is largely a matter of separation between the antennas for similar systems . . . and judicious use of real estate. Once an airplane is airborne, relative differences between top and bottom mounted antennas is insignificant. Then why do large Aircraft often have two com antennae? One on top, Sometimes in the vert stab and one below. The reason for the two antennae is because of shading of the signal to stations directly below the plane (upper antenna) or shading of a other aircraft more or less directly above the plane (Belly position antenna) For some reason Bob I think we are off the same page again. Noel ________________________________ Message 11 ____________________________________ Time: 12:57:30 PM PST US From: "Noel Loveys" Subject: RE: AeroElectric-List: Comm Antenna & SWR: More Information True the ELT antenna should be seen first and foremost by satellites. But they must also be able to be seen by search aircraft. The new 406 ELTs do a much better job of being seen by the satellites (Assuming an open area) and are also more linear than the old 121.5 units thus making them superior for the task they perform. >From here I'm going to go on a bit of a tangent. The new units are programmed to a specific aircraft. The first problem I see with this is as soon as a signal is received it can be identified as a single seat something or the other and not all the resources that could be put in the field will be used. This is selective response and I for one am against it. The next item is because each unit is coded to a particular aircraft it becomes impossible to lend a unit out while one is in for mundane battery changing. The AMO I worked for often loaned out ELTs because we really didn't want to see our customers going off into the wilds nude of the security an ELT can offer. Commercial aircraft are allowed to operate without an ELT on board forup to 90 days if the unit is in for maintenance. Several years ago a party of executives crashed about two miles off the end of one runway at Goose Bay, Labrador in a snow storm. Their ELT had legally been removed for scheduled maintenance. The passengers did survive the crash but froze to death. The wreckage was found several months later when the snow started to melt. Finally pilots will often monitor 121.5 enroute. This is a nice security feature in that a down plane can be found even before a search starts. My preference is a unit which has both frequencies activated and then using something like the SPOT system as a backup. Noel From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: January 27, 2011 11:44 PM Subject: RE: AeroElectric-List: Comm Antenna & SWR: More Information ELT's are designed to be seen by satellites. Until the present 405 Mhz with superior locating capability came along the I recall hearing a report about 20 years ago that for EVERY downed airplane located, ELT was a factor in a very small percentage of those finds . . . about 6% if I recall correctly. Don't know how much better the stats are now. In any case installation of ELT antennas is a "gee I hope this works when and if they need it" kind of design task. There is no place on an airplane that is immune from crash-induced damage. Equipment placement is based on the study of crash history. So when on short final to the rocks, one should endeavor to crash like most other folks crashed such that their ELT survived. Shadowing to the extent that some ground based facility two miles away doesn't hear it is the very least of concerns. 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 On what basis were these installations said to "work fine". Have these installations been reviewed by the ELT manufacturer? I can't imagine anyone signing off on an installation that didn't provide the customary ground plane combined with a good view of the sky assuming the wreckage was still upright. Emacs! Here's the ELT antennas on a Beechjet. Both are installed under a fiberglas fairing just forward of the vertical fin. Emacs! The 121.5 antenna had to be folded over under the fiberglas to clear some ductwork. This distortion caused the ELT to go into "hi SWR shutdown". Emacs! I made the suggestion that we build a top-hat loaded vertical that could be tuned for that location and wouldn't have to be bent over under the fairing. Certification time-line issues shot that idea down. They just widened the window on the SWR monitor to prevent the shutdown. But even with this band-aid approach, close attention was paid to adequate radiation performance and patterns. If one hopes to achieve better than 6% probability of the ELT being useful, one should be wary of pronouncements of "works fine" when deviating from TSO approved manufacturer's recommendations. Horizontal polarization isn't a big thing but not having a ground plane and clearest possible view of the sky is problematic. Bob . . . 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? http://www.matronics.com/Navigator?AeroElectric-List http://forums.matronics.com http://www.matronics.com/contribution http://www.matronics.com/Navigator?AeroElectric-List http://forums.matronics.com http://www.matronics.com/contribution AeroElectric-List Email Forum - http://www.matronics.com/Navigator?AeroElectric-List - MATRONICS WEB FORUMS - http://forums.matronics.com - List Contribution Web Site - -Matt Dralle, List Admin. http://www.matronics.com/contribution No virus found in this message. Checked by AVG - www.avg.com 01/27/11 Bob . . . ________________________________ Message 12 ____________________________________ Time: 03:07:39 PM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: Comm Antenna & SWR: More Information At 03:36 PM 1/28/2011, you wrote: > > > b:???? The VOR antenna whiskers are horizontally polarized > dipole with major lobes fore and aft with nulls off to the > sides. Further, dipole antennas require no ground plane. > >VOR is not a transmitting antenna. The VOR transmitters are on the ground >and are also horizontally polarized. The receive lobes of the antennae are >part insignificant as aircraft do not approach the VOR sideways. When you said: "The important thing with com antennas is good omnidirectional ( all directions ) coverage. A horizontally polarized antenna in a tailcone, outside of having too small a ground plane, will have a dead area in front of the plane and another one behind it. I can't see how this can be considered good for airplanes heading into or away from a control zone." I didn't realize you were talking and an HF Comm trailing wire. As soon as you mentioned horizontally polarized antenna on the tailcone I thought you WERE talking about a VOR antenna which IS commonly mounted on the tail and IS horizontally polarized. A further confusion point was your mention of a control zone (always short range communications). I'm unaware of any control zone services offered on any frequency where an HF trailing wire would be the antenna of choice. The most popular HF antenna for small airplanes produced at Cessna was a wire that ran from the top of cabin to the tip of the vertical fin and then out to one wing-tip. Radiation pattern looked like a dying flower with badly chewed petals. Here's a drawing from a kit I wrote for a U17 HF installation way back when . . . http://tinyurl.com/4eokmk8 > b:No such "null" exists fore and aft. > >Experience as well as radio theory tells me is sure does exist on the tip of >horizontally polarized signals. Agreed, we weren't talking about the same antenna . . . >Then why do large Aircraft often have two com antennae? One on top, >Sometimes in the vert stab and one below. The reason for the two antennae >is because of shading of the signal to stations directly below the plane >(upper antenna) or shading of a other aircraft more or less directly above >the plane (Belly position antenna) Because they have two radios and it's industry practice to have one antenna for each radio and to locate them as far as practical from each other. "Shading" of a potential station right over or below any given antenna is an exceedingly rare event that lasts only seconds at the speeds these airplanes fly. Just got off the phone with a high-school buddy who's been an ATP since about 1965. With 18K hours in everything from DC-3's with dual ADF to Boeings with cockpits full of glass, he tells me he's never seen any difference in performance between top and belly mounted antennas. He's a ham too and speaks/understands radioeze . . . >For some reason Bob I think we are off the same page again. Correct. HF antennas on light aircraft are EXCEEDINGLY inefficient, e-field antennas and unless 'bent', they'll have strong nulls off the ends irrespective of polarization. I thought we were talking about aviation antennas likely to be installed on airplanes flown by members of this List. Bob . . . ________________________________ Message 13 ____________________________________ Time: 04:28:10 PM PST US From: "Noel Loveys" Subject: RE: AeroElectric-List: ELT antenna performance Thanks Dick... I was unaware there even was a millihertz. In English class many snows ago we were told when it came to abbreviations, the rule was only capitalize measurements which were peoples' names. Under that rule mHz would be correct for either millihertz or megahertz or even gHz...gigahertz. Noel From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Richard Tasker Sent: January 28, 2011 12:45 PM Subject: Re: AeroElectric-List: ELT antenna performance Hey Bob, not to pick nits , but you are the example here after all... ;-) mHz - millihertz MHz - megahertz Dick Tasker Robert L. Nuckolls, III wrote: When I first got into electronics as a profession, I was working for a two-way radio company in Wichita. We serviced a few systems in the 72 mHz band but most were in the vicinity of 150 mHz and a few were up about 450. This was all vacuum tube stuff. The 450 mHz equipment was at the upper fringe of what was practical. It was harder to develop power, losses in feedlines was higher, keeping receiver sensitivity to less than 1 microvolt was more demanding. All-in-all, higher cost of ownership. You'd think that customers would shy away from this equipment. On the contrary. Antennas were more efficient. Terrestrial noise was a small influence. Signals behaved much better in the confines of tall buildings. The cab companies wouldn't have anything different. The police wanted it but the FCC decreed that public services will conduct business in the 150 mHz band. 150 mHz was subject to much more multi- path nulls and noise. 121.5 mHz was picked for the first ELTs because it was a frequency already serviced by aviation communication services. Same with 243 albeit military. ________________________________ Message 14 ____________________________________ Time: 04:28:10 PM PST US From: "Noel Loveys" Subject: RE: AeroElectric-List: ELT antenna performance Don't feel in the slightest bad Bob... I'm guilty too. Noel -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: January 28, 2011 1:47 PM Subject: Re: AeroElectric-List: ELT antenna performance At 11:15 AM 1/28/2011, you wrote: >Hey Bob, not to pick nits , but you are the example here after all... ;-) > >mHz - millihertz > >MHz - megahertz > >Dick Tasker You're quite correct. Unfortunately, when trying to bang out a timely but extensive reply, I don't have the luxury of coming back to edit it tomorrow to attempt a 99% clean posting. When I go back and read my past postings, it's not unusual to get whacked by spelling/semantics issues. I'll just have to beg the Lists indulgence. That doesn't mean I don't want to hear from folks when I've stubbed my toe. Just be forewarned that in spite of your most honorable efforts, my head will probably continue to run out in front of fingers on the keyboard. Thanks for the heads-up! Bob . . . ________________________________ Message 15 ____________________________________ Time: 04:56:26 PM PST US From: Mike Welch Subject: RE: AeroElectric-List: ELT antenna performance > Don't feel in the slightest bad Bob... I'm guilty too. > > Noel > >mHz - millihertz > > > >MHz - megahertz > > > >Dick Tasker Fortunately=2C I can honstly sya=2C I nver make any tpos. : ) Mik e ________________________________ Message 16 ____________________________________ Time: 06:51:58 PM PST US From: Bill Watson Subject: Re: AeroElectric-List: Graphene OK, that's the second time I've heard about this stuff in 24 hours... so, if you want an entertaining survey of modern materials (including a demonstration of graphene production) check this out: http://www.pbs.org/wgbh/nova/tech/making-stuff.html I expected less from this NOVA series but was entertained and informed throughout the first 2 shows. Bill Watson RV10 On 1/26/2011 11:29 PM, Speedy11@aol.com wrote: > 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. > Stan Sutterfield > > > Thin, Light, Strong, and Energy Dense > > by Dean Sigler on 01/07/2011 > > 2010s Nobel Prize in Physics > went > 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. As 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 gas atom, can pass through it. Carbon, the > basis of all known life on earth, has surprised us once again. > > 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 > or about the size of a football field/ > > * > > * ________________________________ Message 17 ____________________________________ Time: 09:58:45 PM PST US From: "John F. Herminghaus" Subject: AeroElectric-List: BNC connectors Bob, I have become aware that BNC connectors have at least two flavors: 50 and 75 ohms. Not being sure which impedance my connectors have I measured the SWR for my com and vor antennas. The com was 1.2 to 3.1 with the 3.1 at 118.0 mhz. Above 119 mhz it was below 2. The vor was between 1.1 and 1.9 over the full frequency range. According to your book, they should be OK. But what about GPS, DME and transponder antennas. Is the impedance of the connector important? In other words should I go to the trouble of making sure all connectors are 50 ohms? John Herminghaus ________________________________ Message 18 ____________________________________ Time: 10:20:43 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: BNC connectors At 12:52 AM 1/29/2011, you wrote: >Bob, > >I have become aware that BNC connectors have at least two flavors: >50 and 75 ohms. Not being sure which impedance my connectors have I >measured the SWR for my com and vor antennas. The com was 1.2 to >3.1 with the 3.1 at 118.0 mhz. Above 119 mhz it was below 2. The >vor was between 1.1 and 1.9 over the full frequency >range. According to your book, they should be OK. But what about >GPS, DME and transponder antennas. Is the impedance of the >connector important? In other words should I go to the trouble of >making sure all connectors are 50 ohms? The connectors are "50 ohm" because they have dimensions conducive to installation on a piece of 50 ohm coax. If your connector fits on the coax, then it's the right connector. Bob . . . ________________________________ Message 19 ____________________________________ Time: 11:39:56 PM PST US From: rayj Subject: AeroElectric-List: OT-potting with RTV silicone do not archive Is RTV silicone acceptable for potting electronics? I know Bob recommends E6000 or equivalent but I have several 1/2 tubes of RTV I'd like to use up. The item I'm potting is the "ballast for some cheap fluorescent fixtures that buzz. I'm hoping I can quiet them down. Thanks for all replies. -- Raymond Julian Kettle River, MN ________________________________ Message 20 ____________________________________ Time: 11:39:56 PM PST US From: "John F. Herminghaus" Subject: Re: AeroElectric-List: BNC connectors Thanks a lot. That's what I suspected and hoped to hear. You saved me a lot ot trouble John On 29.01.2011 06:15, Robert L. Nuckolls, III wrote: > At 12:52 AM 1/29/2011, you wrote: >> Bob, >> >> I have become aware that BNC connectors have at least two flavors: 50 >> and 75 ohms. Not being sure which impedance my connectors have I >> measured the SWR for my com and vor antennas. The com was 1.2 to 3.1 >> with the 3.1 at 118.0 mhz. Above 119 mhz it was below 2. The vor >> was between 1.1 and 1.9 over the full frequency range. According to >> your book, they should be OK. But what about GPS, DME and >> transponder antennas. Is the impedance of the connector important? >> In other words should I go to the trouble of making sure all >> connectors are 50 ohms? > > The connectors are "50 ohm" because they > have dimensions conducive to installation > on a piece of 50 ohm coax. If your connector > fits on the coax, then it's the right > connector. > > 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.