AeroElectric-List Digest Archive

Thu 12/21/17


Total Messages Posted: 8



Today's Message Index:
----------------------
 
     1. 08:25 AM - Re: Re: VHF antenna in the tail (Robert L. Nuckolls, III)
     2. 08:30 AM - The morning smile . ..  (Robert L. Nuckolls, III)
     3. 08:47 AM - Re: The morning smile . ..  (Rene)
     4. 11:43 AM - Re: Electronic Ignition spark advance signal boost (Eric Page)
     5. 04:24 PM - Re: Re: VHF antenna in the tail (GTH)
     6. 05:29 PM - VHF Antenna in tail (Graeme Coates & Sharon Beaman)
     7. 06:05 PM - Re: Electronic Ignition spark advance signal boost (Airdog77)
     8. 08:03 PM - Re: Electronic Ignition spark advance signal boost (Eric Page)
 
 
 


Message 1


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    Time: 08:25:16 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: VHF antenna in the tail
    At 12:14 AM 12/21/2017, you wrote: >As I recall, the characteristic impedance of a folded dipole is 200 >ohms, so you would probably need a 1:4 balun to feed it from 50 ohm coax? > >Bill Actually, closer to 300 ohms. WAAaaayyy back when television Yagis featuring folded driven elements were a close match to 300-ohm twin-lead. Antennas and airplanes just don't really play nicely together . . . the most elegant solution is almost always a compromise . . . a departure from that which can be achieved in terrestrial environs. Fortunately, VHF communications is (1) mostly short range and (2) line of sight. Hence, a few watts of transmitter and a wet string for an antenna will generally put you in contact with the other station. For the build in question, the goal is to get as much of a 1/4 wave, vertically oriented radiator supported on the leading edge of a composite vertical fin . . . which MUST be glass/epoxy structure to minimize RF attenuation. Then, it would be NICE if we could put an 1/4 wave radius ground plane around the base. Emacs! Hmmmm . . . that would make for a funny looking airplane . . . even the first level compromise of crafting a ground plane from multiple radials is out of question. Okay, compromise #3, a SINGLE 1/4 wave element that extends back along the feedline toward the radio. Here's one of dozens of examples in the DIY antenna crowd. https://goo.gl/HXCBzh This article is pretty close. The author stubs his toe in assuming that the velocity factor of the 'bazooka' section is the same as the velocity factor of the coax used to fabricate the feedline and antenna. In fact, velocity factor is a function of dielectric characteristics between two conductors, in this case center conductor and the surrounding shield. For coax, the dielectric is some material designed to hold the center conductor alignment while minimizing losses. It's true that the outer braid of the bazooka does form a coaxial section over the outer braid of the feed line . . . but with a DIFFERENT dielectric which is not low loss center conductor support but a robust outer jacket of the coax that has nothing in common with the RF characteristics of the inner insulation. Hence the velocity factor of the feed line has no relationship to the design of the de-coupling sleeve. This antenna can be installed in a glass/epoxy airplane with the radiating element firmly built into the vertical fin structure. The feed line can be fitted with a de-coupling 'bazooka' . . . and essentially treated as any other feed line. I've got the test equipment necessary to tune the de-coupling sleeve to accommodate the new dielectric/conductor combination . . . but it will probably be after the first of the year before I'll be able to get to it. Bob . . .


    Message 2


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    Time: 08:30:35 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: The morning smile . ..
    Emacs! Bob . . .


    Message 3


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    Time: 08:47:51 AM PST US
    From: "Rene" <rene@felker.com>
    Subject: The morning smile . ..
    My wife would be much more impressed by the C-97. Rene' 801-721-6080 From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: Thursday, December 21, 2017 9:30 AM Subject: AeroElectric-List: The morning smile . .. Bob . . .


    Message 4


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    Time: 11:43:29 AM PST US
    Subject: Re: Electronic Ignition spark advance signal boost
    From: "Eric Page" <edpav8r@yahoo.com>
    Wade, here's a small (1.46" x 0.56") PCB to carry Bob's suggested circuit plus a voltage regulator... https://oshpark.com/shared_projects/xwyh5mon ...and here's a Digi-Key shopping cart with the necessary parts... http://www.digikey.com/short/qqfnwm Connect 'IN+' to the Electroair ignition module advance signal and 'IN-' to the Electroair local ground. Connect 'BUS' and 'GND' to 12V and ground, and 'OUT' to the desired EIS input. If you'd like, I'm happy to put this together and send it along with the other stuff. It will be about $22.50 with the shipping and tax from Digi-Key. I can just add this to the PayPal invoice for the voltage slump eliminator. Eric Read this topic online here: http://forums.matronics.com/viewtopic.php?p=476673#476673


    Message 5


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    Time: 04:24:12 PM PST US
    Subject: Re: VHF antenna in the tail
    From: GTH <gilles.thesee@free.fr>
    Hi all, Thanks to all who responded. Indeed the dipole is out of the question and we'll have to go the 1/4 wave route. /Le 21/12/2017 17:24, Robert L. Nuckolls, III a crit : / > / > Okay, compromise #3, a SINGLE 1/4 wave element that > extends back along the feedline toward the radio. Here's > one of dozens of examples in the DIY antenna crowd. > > / /https://goo.gl/HXCBzh/ Most interesting. Maybe this as something in common with the Becker 1A005 ? http://www.beckerusa.com/Products/1a005-2/ Which we find too expensive at ~100 . > > > / > I've got the test equipment necessary to tune > the de-coupling sleeve to accommodate the new > dielectric/conductor combination . . . but it > will probably be after the first of the year > before I'll be able to get to it. / I'd be most interested in your findings in order to craft a bazooka for an acceptable VHF antenna in the tail fin. Thanks again, -- Best regards, Gilles http://contrails.free.fr http://lapierre.skunkworks.free.fr


    Message 6


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    Time: 05:29:45 PM PST US
    Subject: VHF Antenna in tail
    From: Graeme Coates & Sharon Beaman <coatbeam@melbpc.org.au>
    Hi Jim Weir designed a copper tape antenna years ago. See sport Aviation Jan 1981 (attached) and http://www.rst-engr.com/rst/products/plasticplaneantenna/plasticplaneantenna_files/2802%20Manual-s.pdf Very simple and cheap. > Time: 07:05:33 AM PST US > Subject: Re: AeroElectric-List: VHF antenna in the tail > From: GTH <gilles.thesee@free.fr> > > /Le 20/12/2017 02:41, GTH a crit : > / >> / >> On the attached picture of the rear half-fuselage, the glass fin can >> be seen, with the carbon fiber tail cone at the base. A small number >> of foam ribs will be added. >> >> Question 1 : What would be the lightest and most inexpensive way to >> construct an efficient VHF antenna housed in the tail fin ? >> Question 2 : Will it be necessary to build a glass fiber rudder, or >> will carbon fiber be acceptable (weight concern) ? >> / >> > Hi all, > > Thank you everyone who responded. > The project is a small airplane with the fin about 800 mm high (~950 mm > leading edge), so space seems a bit limited for a dipole antenna. > Still looking into any solution. > The idea is to design something mostly DIY for cost reasons, so this > seems to rule out off-the-shelf antennas. > Any ideas ? > > BTW, what is the influence of the radiating element width/diameter vs > selectivity or else ? > Any hard facts on the subject ? > > Thanks for any input, > >


    Message 7


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    Time: 06:05:42 PM PST US
    Subject: Re: Electronic Ignition spark advance signal boost
    From: "Airdog77" <Airdog77@gmail.com>
    Eric, If you're sure you don't mind, that would be a huge help... Thanks a million! (And to all the others collaborating on this). Warm regards and Merry Christmas, Wade -------- Airdog Wade Parton Building Long-EZ N916WP www.longezpush.com Read this topic online here: http://forums.matronics.com/viewtopic.php?p=476681#476681


    Message 8


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    Time: 08:03:15 PM PST US
    Subject: Re: Electronic Ignition spark advance signal boost
    From: "Eric Page" <edpav8r@yahoo.com>
    No problem. Lately I've been a little low on things to do in my "off" time, so I'd be glad to build it. Parts and boards are ordered. Eric Read this topic online here: http://forums.matronics.com/viewtopic.php?p=476682#476682




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