---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 04/15/10: 12 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:56 AM - Re: Re: copper foil groundplane () 2. 07:36 AM - noise suppression (Jean Lowenhardt) 3. 08:43 AM - The Miracle Whip series antennas (Robert L. Nuckolls, III) 4. 08:49 AM - Re: noise suppression (Robert L. Nuckolls, III) 5. 09:03 AM - Noise suppression (Jean Lowenhardt) 6. 09:03 AM - 1/2 Wave Ring Antenna (user9253) 7. 09:45 AM - Re: The Miracle Whip series antennas (Robert L. Nuckolls, III) 8. 10:05 AM - Re: 1/2 Wave Ring Antenna (Robert L. Nuckolls, III) 9. 10:24 AM - Battery maintenance philosophies to meet design goals (Robert L. Nuckolls, III) 10. 10:56 AM - Re: 1/2 Wave Ring Antenna (Fisher Paul A.) 11. 03:09 PM - Accurate Altitude and Airspeed () 12. 07:51 PM - Re: 1/2 Wave Ring Antenna (Tim Shankland) ________________________________ Message 1 _____________________________________ Time: 06:56:46 AM PST US Subject: RE: AeroElectric-List: Re: copper foil groundplane From: Thanks, Actually I'd pay $90 just for the packaging. I've now seen some of the homemade jobs and while I've not clue on how to build antennas, I have less of clue how any of these folks got their inventions in the airplane. Copper strips, pipe, soldering, 3 ft tall, etc. etc. I have a Lancair not a Suburban. $90.00 is a no brainer. Thanks for the reference. Do Not Archive. Glenn -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of checkn6 Sent: Wednesday, April 14, 2010 5:32 PM Subject: AeroElectric-List: Re: copper foil groundplane Inside the magic box Read this topic online here: http://forums.matronics.com/viewtopic.php?p=294242#294242 Attachments: http://forums.matronics.com//files/themiracleinside_131.jpg ________________________________ Message 2 _____________________________________ Time: 07:36:22 AM PST US From: "Jean Lowenhardt" Subject: AeroElectric-List: noise suppression Installation instructions for a 12volt, 8amp wind driven generator specify shielding on the output lead with no other noise suppression requirements. Electrical system schematics for later models of the aircraft, having engine driven generators, specify 0.01 microfarad capacitors on the armature and stator leads. On the wind driven generator, the regulator is housed within the generator unit and the only external wires are the output and ground leads. Should a capacitor be installed on the wind driven generator output lead at the generator terminal for noise suppression in addition to the original shielding requirement? If a capacitor is recommended, it must be weather resistant. Therefore, please advise on part number and source information if a capacitor is recommened. Thanks for any input to my question and request. ________________________________ Message 3 _____________________________________ Time: 08:43:55 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: The Miracle Whip series antennas Robert Victor, President (VA2ERY) Miracle Antenna Montreal, Canada Good morning sir, By way of introduction, I'm an electronics engineer retired from Hawker-Beechcraft after 46 years in the electronics trades with an emphasis on aircraft. I have a hobby business that supports the owner built and maintained aircraft industry. My website is at http://aeroelectric.com I've been moderating electrical/electronics discussion forums for amateur builders on Matronics for over 10 years. Our current membership is about 1800. I also publish a document intended to assist my readers in the crafting of failure-tolerant electrical systems; https://matronics.com/aeroelectric/Catalog/pub/pub.html#P-Book I was asked about VHF Com and VOR antennas suitable for installation inside a composite aircraft. One reader pointed out your offerings for a end-fed, half-wave antenna specific to that task. I've reviewed this and ancillary products on your website and in various postings to the Internet. Without a doubt, the end-fed, half-wave configuration offers an opportunity but it also has some special needs for impedance matching. Have you performed antenna range testing on the VHF aircraft antennas? Have you published any performance data for this device over the frequency range of interest? Have there been any studies of radiation patterns associated with recommended installation methods? I would like to be capable of advising my readers from a position of knowledge and understanding about your products. Anything you can offer to assuage my ignorance would be appreciated. I'd like to add this technology to the discussion on antennas when the book is updated. Finally, would you be willing to consign an exemplar antenna to me for testing in local facilities? I'd be pleased to return it to you along with any data that is developed from the testing efforts. Kindest regards, Bob Nuckolls (K0DYH) AeroElectric Connection P.O. Box 130 Medicine Lodge, KS 67104-0130 Land line: (620) 886-3403 Mobile: (316) 209-7528 ________________________________ Message 4 _____________________________________ Time: 08:49:32 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: noise suppression At 09:31 AM 4/15/2010, you wrote: >Installation instructions for a 12volt, 8amp wind driven generator >specify shielding on the output lead with no other noise suppression >requirements. Shielding of such leads is a pointless effort. Any noise produced by the generator will be CONDUCTED along its power feed wire, not electro-statically coupled to other potential victims. >Electrical system schematics for later models of the aircraft, >having engine driven generators, specify 0.01 microfarad capacitors >on the armature and stator leads. On the wind driven generator, the >regulator is housed within the generator unit and the only external >wires are the output and ground leads. >Should a capacitor be installed on the wind driven generator output >lead at the generator terminal for noise suppression in addition to >the original shielding requirement? If a capacitor is recommended, >it must be weather resistant. Therefore, please advise on part >number and source information if a capacitor is recommened. >Thanks for any input to my question and request. Try it and see. The responsible supplier will conduct noise tests in a lab and supply necessary noise suppression technology as part of the product. If the as-delivered generator didn't come with filters (and they're not called out on installation instructions) then an assumption follows that no filtering is needed. Some rudimentary flight-testing after installation will go to proving/disproving that assumption. Come back to this discussion with your findings if indeed the critter turns out to be noisy. Bob . . . ________________________________ Message 5 _____________________________________ Time: 09:03:57 AM PST US From: "Jean Lowenhardt" Subject: AeroElectric-List: Noise suppression Installation instructions for a 12volt, 8amp wind driven generator specify shielding on the output lead with no other noise suppression requirements. Electrical system schematics for later models of the aircraft, having engine driven generators, specify 0.01microfarad capacitors on the armature and stator leads. On the wind driven generator, the regulator is housed within the generator unit and the only external wires are the output and ground leads. Should a capacitor be installed on the wind driven generator output lead at the generator terminal for noise suppression in addition to the original shielding requirement? If a capacitor is recommened, it must be weather resistant. Therfore, please advise on part number and source information if a capacitor is recommened. Thanks for any input to my question and request. Hugh Loewenhardt aeronca2@99main.com restoring Fairchild 24C8C, N15076 Stonington, Ct ________________________________ Message 6 _____________________________________ Time: 09:03:58 AM PST US Subject: AeroElectric-List: 1/2 Wave Ring Antenna From: "user9253" Has anyone ever experimented with a 1/2 Wave Ring Antenna? It is described here: http://www.slvrc.org/902band/902antennas.htm It could be mounted on a metal turtle deck and covered with non-conductive fabric or fiberglass for streamlining. Its low profile would have less drag than a quarter wave antenna at high speeds. Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=294317#294317 ________________________________ Message 7 _____________________________________ Time: 09:45:20 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: The Miracle Whip series antennas At 10:41 AM 4/15/2010, you wrote: > > >Robert Victor, President (VA2ERY) >Miracle Antenna >Montreal, Canada > >I would like to be capable of advising my readers >from a position of knowledge and understanding about >your products. Anything you can offer to assuage my >ignorance would be appreciated. I'd like to add >this technology to the discussion on antennas when >the book is updated. I received a pleasant phone call from Mr. Victor. He was unwilling to share any test data . . . backed by the notion that such sharing left his venture open to competition by folks who might exploit his IR&D efforts. This is a real risk for simple, easily fabricated products. He did offer the idea that the Miracle Whip was not an end-fed but center-fed half-wave dipole. He explained that the dipole is formed by exposing 1/4-wave of center conductor of the far end of the feed line. One then moves 1/4-wave toward the transmitter and inserts a high efficiency, common- mode choke. That's what the 7-turns of coax through the torroid core is all about. This inserts a discontinuity in the shield. The effect is that the INSIDE of the coax is a feed-line out to the center and the outside of the coax shield beyond the choke becomes one-half of the dipole. This means that the "wire" we see wrapped through the core in . . . >http://forums.matronics.com//files/themiracleinside_131.jpg is actually an unbroken length of coaxial cable. The magic comes from core selection for high permeability while offering the lowest possible losses at VHF frequencies. No doubt a high quality ferrite material. When I get the RF bench running fully and have the time, I'll fiddle with the concept a bit and see what I can confirm with the test equipment. Bob . . . ________________________________ Message 8 _____________________________________ Time: 10:05:22 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 1/2 Wave Ring Antenna At 11:02 AM 4/15/2010, you wrote: > >Has anyone ever experimented with a 1/2 Wave Ring Antenna? It is >described here: >http://www.slvrc.org/902band/902antennas.htm >It could be mounted on a metal turtle deck and covered with >non-conductive fabric or fiberglass for streamlining. Its low >profile would have less drag than a quarter wave antenna at high speeds. I'm planning on building a cousin to this antenna for my 2M storm watch transceiver. See: http://www.antennex.com/preview/2mddrr.htm This is the 1/4 wave version. Given that both the 1/4 and 1/2 wave antennas are vertically polarized says that all the magic happens in that short vertical mast that goes to ground. This becomes the same thing as a short vertical with a strong top-hat loading scheme. So whether the "top hat" is 1/4 or 1/2 wave in circumference probably offers little difference in performance. Given the lengthening effect of so severe a "rake angle" on this antenna, the physical length of a 1/4-wave will be shorter than the classic 22" whip. 22" bent around in a circle would give us less than 6" diameter and about 2" tall for VHF Comm frequencies. This cross section, even if well faired, could offer much more drag than the simple whip stuck out in the breeze. However, this form of antenna might perform well inside a composite fuselage. The biggest problem with heavily loaded antennas is loss of band-width. They tend to be sharply tuned at the design frequency with efficiency falling off rapidly either side. The extreme example of this phenomenon is demonstrated by small diameter loop antennas for lower ham frequencies. They have to be fitted with motor driven capacitors to allow remote tuning to the frequency of interest. Circulating currents tend to be very high, voltage across the tuning capacitor is quite high. To keep the losses low at such high currents, the antenna is made from 3" DWV copper! The DDRR antenna needs a high conductivity ground plane that's at least 2x the antenna diameter. So a 6" DDRR might be built on a 12" square piece of copper clad that could become a "shelf" of sorts in the tailcone. Further, that same sheet might also be a good mounting location for the transponder antenna. Food for thought. Bob . . . ________________________________ Message 9 _____________________________________ Time: 10:24:52 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Battery maintenance philosophies to meet design goals >If I'm going to ask an opinion of someone on the list, then I >certainly must provide accurate information - or expect no answer. >I'm using Odessey and happy with it so far. I have no intention of >changing at this time. But, I was interested in the answer to the >proposed question. I am always interested in a less expensive, but >adequate replacements for equipment. >Perhaps changing a battery each year is a waste of money. And I've >been called an old FUDdy before, but it is certainly not out of >fear, uncertainty, or doubt. >I change a battery a year because: > >1. It is recommended by an expert in the field - Electric Bob I did NOT recommend it. I suggested it as an option to be considered and adopted pending YOUR assessment of design goals, ways in which you choose to spend your $time$ and tools you plan to acquire to execute a considered preventative battery maintenance program. >2. My ignorance dictates that I listen to the experts I'd rather you use my offerings more as teacher than as expert. If you don't understand the fundamentals upon which best decisions are made, then you are at risk for falling victim to anyone who wraps themselves in the mantle of "expert" >3. It establishes a reasonable means to avoid failure Let us assume you're going to buy a Hawker-Enersys super battery of some kind and you plan to run it until no longer suitable for flight? What criteria and tools to YOU plan to use to monitor that condition? Whether you swap every year or run it until no longer suited for flight, the means by which you avoid 'failure' lies entirely in your lap, not the suggestions of anyone else on the list. >4. It is not overly expensive If it's not the LEAST expensive, then don't do it. >5. The batteries are used in other equipment and not wasted. Can you quantify "wasted"? Let's say you install a shiny new 18 a.h. battery and your endurance analysis shows that you need 12 a.h. at a 3 hour rate to meet your battery only endurance goals. When it's time to replace that battery, it will still be cranking the engine just fine. When you swap out an el-chesso battery at one year, it too will still be cranking the engine just fine. Both scenarios will remove a battery from your AIRPLANE that may still have some degree of usefulness NOT in an airplane. Which scenario offers the most/least "waste"? >6. The oldest battery at any moment in my RV is 2 years. So is the main battery (which I presume was new last year) going to replace the 2-year old aux battery soon? >7. I don't have to bother with capacity checks I prefer to express it differently. You battery preventative maintenance program is optimized to expend the minimum $time$ to insure compliance with your design goals. >I also change my tires before they fail. Anyone who wants the old >ones just let me know. Boy . . . do I remember those days! There was a Texaco station owner who took pity on me and gave me a call when he had extra-ordinarily meaty take-off tires I could buy. >I change my hoses before they fail. Anybody want the old ones? Naw . . . ran too many of those until they blew . . . >I don't like being stranded in remote locations because I tried to >stretch the life of consumables such as batteries. In this case, the "stretching" thing doesn't have much tension in it. Unless you're installing big lead pigs with the idea that your battery-only endurance requirements can be met with only 25% of as-new capacity, then maybe you would stretch it. Now, Z13/8 does offer an opportunity to take battery capacity completely out of the FMEA study for endurance. Cranking the engine is a pretty good test of a battery to be MINIMALLY functional where a second, engine driven power source replaces the battery as the stand-by power source. >Just call me an old fuddy. Old fuddies are those among us who allow our airplanes to get WAAaaayyyy ahead of us. For many of our brethren in the TC aircraft world, the airplane is probably too far "out in front" . . . and they don't have to be grey- haired to suffer this condition! This assertion is supported by the many dark-n-stormy-night stories we've read and analyzed on the List over the years. I'll respectfully suggest that if folks are participating here just to ask for and run with an answer that appears delivered with some expertise, you may be better off sticking with a C-172 style electrical system. The value to be gathered here is not the advise of experts or a mass of anecdotal experience. It's my fondest wish that folks flying systems crafted from ideas offered here UNDERSTAND what's going on and are in command and control of their electro-whizzy destiny. >Ira, thanks for researching the correct info on the battery and >providing your opinion. I appreciate it. >It appears from your comment that you prefer Panasonic >batteries. Which model do you use? Why do you believe that battery >is better than an Odessey? Panasonic makes no product on a par with Hawker- Enersys. My studies of aircraft battery products have convinced me and my colleagues that H-E products are the cream of the battery crop. In no way should that statement be interpreted to mean that Panasonic products do not offer good value. Only the builder/operator of an OBAM aircraft can make the determination of value based on their own cost-of-ownership studies. > Does it have more AH capacity? Does it have faston tabs or screw > on terminals? There's a collection of battery manufacturer's data including Panasonic and H-E on my website at: http://aeroelectric.com/Mfgr_Data.html >Your suggestion of replacing a battery every two years seems like a >reasonable thing to do - especially if one charges the batteries to >capacity periodically. How do we quantify "reasonable" . . . how many watt seconds of energy are expected to be contained in an 18 ah battery after 2 years of "reasonable" use and maintenance? Please don't think I'm picking on you my friend. I think it's important that words be crafted to illustrate well considered recipes for success. It's important that meaning/understanding is not sacrificed to misinterpretation. Bob . . . ________________________________ Message 10 ____________________________________ Time: 10:56:44 AM PST US From: "Fisher Paul A." Subject: RE: AeroElectric-List: 1/2 Wave Ring Antenna There has been some discussion about a ring antenna here: http://www.vansairforce.com/community/showthread.php?t=52676 The discussion was specifically about APRS which uses 144.39MHz in the ham bands, but it's close enough to aviation frequencies that it might give you some ideas. The biggest issue on this thread is where do you mount such an antenna in an all metal airframe. Obviously, the problem becomes much simpler if you eliminate that! Paul A. Fisher Q-200, N17PF - copper foil dipole embedded in the vertical tail RV-7A, N18PF - 1/4 wave sticking out in the wind! -----Original Message----- From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of user9253 Sent: Thursday, April 15, 2010 11:02 Subject: AeroElectric-List: 1/2 Wave Ring Antenna Has anyone ever experimented with a 1/2 Wave Ring Antenna? It is described here: http://www.slvrc.org/902band/902antennas.htm It could be mounted on a metal turtle deck and covered with non-conductive fabric or fiberglass for streamlining. Its low profile would have less drag than a quarter wave antenna at high speeds. Joe -------- Joe Gores ________________________________ Message 11 ____________________________________ Time: 03:09:06 PM PST US From: Subject: AeroElectric-List: Accurate Altitude and Airspeed 4/15/2010 Hello Mike, You wrote: "Not sure why this (altitude variation with airspeed) would be, or more importantly, how to fix it." Hello Bernie, You wrote: "There didn't seem to be any theory behind it." This is not a very rare or mysterious phenomena. Inaccurate airspeed indications can be caused by inaccurate dynamic and static air pressure forces. Inaccurate altitude indications can be caused by inaccurate static pressure forces. AIRSPEED. Let's talk about inaccurate airspeed measurements first. An airspeed indicator is a balancing mechanism. It balances the difference between a force created by dynamic air pressure and a force created by static air pressure. The force from the dynamic air pressure is the result of the forward movement of the airplane. The faster the airplane moves the greater the force exerted. In order to get an accurate measure of that dynamic force one needs to accurately sense the free stream dynamic air pressure and send it to the airspeed indicator via leak and kink free tubing. That means sensing the air movement in the actual direction that the airplane is moving and having that air movement not affected by some local air flow direction change caused by the airframe itself. This is why you sometimes see flight test airplanes with a long boom sticking out forward with a small vane mechanism on the front of it. This boom and vane mechanism, along with connecting tubing, is a pitot tube system intended to accurately measure the force from the free stream dynamic air pressure without any inaccuracies introduced by local airframe air flow. See Note One below. So much for the dynamic force side of the airspeed indicator balancing act, what about the static force side? An accurate static force is provided by a static port ideally located somewhere on the airframe such that it is measuring the true static air pressure. But finding that ideal location and making the perfect static port that does not introduce static air pressure errors is not always so quick and easy. And what do we do if we discover that the static port that we have installed is not producing accurate static air pressure? See Note Two below. ALTITUDE. An altimeter is also a balancing mechanism. It measures the difference between the initial altitude setting of the altimeter mechanism as compared to the static air pressure encountered by that same mechanism while in flight and displays that difference in some lineal measurement (usually in feet in our part of the world). If the static pressure provided to the altimeter via the static port and the connecting tubing is in error or changes with the airplane's airspeed, when the actual altitude is constant, then the altimeter's altitude indication will be in error. And what do we do if we discover that the static port that we have installed is not producing accurate static air pressure? See Note Two below. 'OC' Says: "The best investment we can make is the effort to gather and understand knowledge." Note One: Why don't we use these long boom and vane type pitot tubes on our experimental amateur built aircraft? Because the boom and vane would take a terrific beating from people walking into them on the ground and because the dynamic force errors introduced by the type of pitot tubes that we commonly use are just not great enough to cause us concern. There is not very much we can do about adjusting the force coming from dynamic air pressure other than using a pitot tube located a sufficient distance from a disturbing piece of airframe (usually the bottom surface of a wing) and avoiding a leak or kink in the tubing going from the pitot tube to the airspeed indicator. Note Two: So we have built our airplane, installed our static port(s), and discovered that we are getting inaccurate airspeed and / or altitude indications and decide to do something about it. We could just go on installing new static ports in different locations, but that is a lot of work and we are not assured of better results. So we should do just what the big boy aerodynamic types do, we fudge or bandaid as needed to get the air to give us the results that we want. Let's say that the airspeed indicator is reading too high -- it says the airplane is going faster than it really is. (See Note Three). The dynamic air pressure side of the airspeed indicator is providing too much force in the desired balancing act. How can we counteract that excess dynamic force? We increase the static force being fed to the airspeed instrument by the static port by installing a small wedge just aft of the opening on the static port (thin edge of the wedge facing forward towards the hole). This small wedge causes air to pile up and increase the static air pressure going to the airspeed indicator (and also to the altimeter unless you have provided separate static ports for the two instruments) and give us the accurate force balance measurement that we want. Let's say that the altimeter reading goes down 200 feet when you speed up 60 miles per hour (Mike, you did not say which direction your altitude was changing with the changes in airspeed). This means that the static port is feeding greater than static pressure as your airplane flies faster. How can we reduce that undesired increase in static air pressure? We install a small wedge in front of the hole in the static port (thin edge of the wedge facing aft towards the hole) to shield it a bit from dynamic air pressure coming from the front in order to get a more stable and accurate altitude reading. How do we get the right size wedge facing the correct direction to get the airspeed and altitude results that we want? The same way the big boys do: TRIAL AND ERROR and MORE TRIAL AND ERROR. Because our airplanes are experimental, amateur built we are permitted to do just that -- experiment. Note Three: So now we know how to tweak our static port(s) to give us accurate airspeed and altitude information, but how do we know that the airspeed and altitude information is inaccurate in the first place and during our trial and error efforts how do we know when we have achieved the accuracy that we are seeking? The answer to those two questions is not as simple as one might first expect. I won't attempt to answer them here because the answers are too big and complex to answer in this forum. What I will suggest is that the reader google "accurate airspeed" and "accurate altitude" and delve into those subjects to the level desired. Here is just one source you will find: http://gpsinformation.net/main/altitude.htm Note Four: This is a personal view point. There are several methods available for determining accurate true airspeed. Some rather elaborate -- some use GPS. Just google "accurate airspeed using GPS". One thing that I've never quite understood regarding these methods is the focus on precisely determining airspeed accuracy indication in the cruising airspeed range. If I determine that my airspeed indicator shows 150 knots indicated airspeed and I determine through some elaborate scheme that I am actually only going 145 knots through the air what do I do with that information? Being 5 nautical miles short of my destination after a one hour flight is a trivial naviagation error contribution compared to all the other error sources (such as heading, wind, and climb airspeed) that I have to contend with and should overcome anyway by some means of real time enroute navigation. I think that if I were going to invest a lot of time and effort in determining my exact airspeed error I would be inclined to do that determination in the approach airspeed arena, not the cruising airspeed arena. And even then I would not be obsessed with absolute airspeed accuracy, I'd just want to know what number on the indicator gives me the right kind of safe approach and landing time after time. ================================================ ----- Original Message ----- From: Cc: "mike mccann" ; "Pulsar builders" Sent: Thursday, April 15, 2010 9:18 AM Subject: Re: Here's an odd question >I noticed that the back half of the round washer where the static exits on > the SR22 had the back half of it filed down so there was in effect a > little shield protecting the static exit hole. ((Sorry about this > description.) > > I asked the people at their booth why they did that. I think I attended > four air shows before I found someone who was involved with the > engineering of the system. The answer - - - - "That is what we had to do > to make the system work right". There didn't seem to be any theory behind > it. They indicated that they had to fiddle around to get it to behave the > way they wanted. Maybe they were just trying to get rid of me. > > In any event, I did the same with mine and it works fine. > > Bernie Wilder ============================================= >> >> ----- Original Message ----- >> From: mike mccann >> To: Pulsar builders >> Sent: Thursday, April 15, 2010 5:06 AM >> Subject: Here's an odd question >> >> >> All, >> >> Utilizing a GPS, I've found that my altimeter in my Pulsar varies with >> changes in airspeed (altitude will change 100-200 feet with speed >> changes of 60 mph). >> >> Has anyone ever heard of this. Not sure why this would be, or more >> importantly, how to fix it. >> >> Many thanks, >> >> Mike >> >> Pulsar 1 >> N116Km ________________________________ Message 12 ____________________________________ Time: 07:51:09 PM PST US From: Tim Shankland Subject: Re: AeroElectric-List: 1/2 Wave Ring Antenna Boy that brings back memories I had a two meter halo antenna on the back of my car in the the 1960's, the principle advantage was that it was horizontally polarized like most of the other hams base station's. By the way a much younger version of myself is the middle one of the group. Tim Shankland 601HD flying ( no halo antenna) Robert L. Nuckolls, III wrote: > > > At 11:02 AM 4/15/2010, you wrote: > >> >> >> Has anyone ever experimented with a 1/2 Wave Ring Antenna? It is >> described here: > > >> http://www.slvrc.org/902band/902antennas.htm > > >> It could be mounted on a metal turtle deck and covered with >> non-conductive fabric or fiberglass for streamlining. Its low >> profile would have less drag than a quarter wave antenna at high speeds. > > > I'm planning on building a cousin to this antenna for > my 2M storm watch transceiver. See: > > http://www.antennex.com/preview/2mddrr.htm > > This is the 1/4 wave version. Given that both the > 1/4 and 1/2 wave antennas are vertically polarized > says that all the magic happens in that short vertical > mast that goes to ground. This becomes the same thing > as a short vertical with a strong top-hat loading > scheme. So whether the "top hat" is 1/4 or 1/2 wave > in circumference probably offers little difference in > performance. > > Given the lengthening effect of so severe a > "rake angle" on this antenna, the physical length > of a 1/4-wave will be shorter than the classic > 22" whip. 22" bent around in a circle would give > us less than 6" diameter and about 2" tall for VHF > Comm frequencies. This cross section, even if well > faired, could offer much more drag than the simple > whip stuck out in the breeze. > > However, this form of antenna might perform well > inside a composite fuselage. > > The biggest problem with heavily loaded antennas > is loss of band-width. They tend to be sharply > tuned at the design frequency with efficiency > falling off rapidly either side. The extreme example > of this phenomenon is demonstrated by small diameter > loop antennas for lower ham frequencies. They > have to be fitted with motor driven capacitors to > allow remote tuning to the frequency of interest. > Circulating currents tend to be very high, voltage > across the tuning capacitor is quite high. To keep > the losses low at such high currents, the antenna > is made from 3" DWV copper! > > The DDRR antenna needs a high conductivity ground > plane that's at least 2x the antenna diameter. So > a 6" DDRR might be built on a 12" square piece of > copper clad that could become a "shelf" of sorts > in the tailcone. Further, that same sheet might > also be a good mounting location for the transponder > antenna. Food for thought. > > 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.