---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 06/22/21: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 10:08 AM - Archer style wingtip antenna fabrication questions (Charlie England) 2. 01:15 PM - Re: Archer style wingtip antenna fabrication questions (user9253) 3. 01:58 PM - Re: Re: Archer style wingtip antenna fabrication questions (Charlie England) 4. 08:48 PM - Re: Archer style wingtip antenna fabrication questions (Robert L. Nuckolls, III) 5. 08:57 PM - Re: Re: Archer style wingtip antenna fabrication questions (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 10:08:21 AM PST US From: Charlie England Subject: AeroElectric-List: Archer style wingtip antenna fabrication questions I have an Archer wingtip comm antenna I intend to install in one wingtip (can always add a 1/4 wave whip if needed), and I'm thinking about building the nav version detailed in Bob's 'Antennas & Feedlines chapter for the other wingtip (figure 13-12 in my document). How critical is the material for the .032" x .8" x 3.25" bakelite insulator that forms what I'm guessing is a matching capacitor? Does the bakelite participate in any way in operation, or is it simply a way to get a fixed air gap? Bakelite in that 'thinness' doesn't seem to be available without paying more for shipping than the 3-postage-stamp size needed would cost. What about substituting something like the thin HDPE cutting board stock, available at discount stores? Two layers would be about .034" thick. Thanks, Charlie ________________________________ Message 2 _____________________________________ Time: 01:15:36 PM PST US Subject: AeroElectric-List: Re: Archer style wingtip antenna fabrication questions From: "user9253" Charlie, It looks like the critical dimension is the 0.31 air gap. My concern is that a softer plastic will flow over time resulting in the screws loosening up. It looks like the angle part of the antenna is fastened to an aluminum wing rib. The directions are not specific. A Bakelite sheet on eBay costs $5 including shipping. Item #: 281793575532 from China. You might have to wait up to a month for shipping. It is 1mm thick which converts to 0.039". I would not sand it down. The Bakelite could possibly contain asbestos. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=502533#502533 ________________________________ Message 3 _____________________________________ Time: 01:58:56 PM PST US Subject: Re: AeroElectric-List: Re: Archer style wingtip antenna fabrication questions From: Charlie England On 6/22/2021 3:14 PM, user9253 wrote: > > Charlie, It looks like the critical dimension is the 0.31 air gap. My concern is that a softer plastic will flow over time resulting in the screws loosening up. > It looks like the angle part of the antenna is fastened to an aluminum wing rib. The directions are not specific. A Bakelite sheet on eBay costs $5 including shipping. Item #: 281793575532 from China. You might have to wait up to a month for shipping. It is 1mm thick which converts to 0.039". I would not sand it down. The Bakelite could possibly contain asbestos. > > -------- > Joe Gores Your ebay-Foo is obviously better than mine; all the hits I got were for much thicker stuff. Thanks for the link! -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ________________________________ Message 4 _____________________________________ Time: 08:48:48 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Archer style wingtip antenna fabrication questions At 12:03 PM 6/22/2021, you wrote: >I have an Archer wingtip comm=C2 antenna I intend >to install in one wingtip (can always add a 1/4 >wave whip if needed), and I'm thinking about >building the nav version detailed in Bob's >'Antennas & Feedlines chapter for the other >wingtip (figure 13-12 in my document). > >How critical is the material for the .032" x .8" >x 3.25" bakelite insulator that forms what I'm >guessing is a matching capacitor? Does the >bakelite participate in any way in operation, or >is it simply a way to get a fixed air gap? > >Bakelite in that 'thinness' doesn't seem to be >available without paying more for shipping than >the 3-postage-stamp size needed would cost. What >about=C2 substituting something like the thin HDPE >cutting board stock, available at discount >stores? Two layers would be about .034" thick.=C2 It IS critical . . . yes it forms the dielectric for a capacitor used to series resonate the feeder strut. Bob must have conducted experiments to optimize the characteristics of that capacitor with respect to the matching strut for optimal mid-band impedance match. If it were my project, I'd use ANY available dielectric material and conduct experiments over a ground plane on the table to achieve (1) antenna resonance and (2) best match to the feed line. When I was a kid, a 'gamma match' was commonly used to bring a feed line and antenna radiator into functional harmony. The attached figure illustrates an adjustable feeder strut paired with a variable capacitor to feed a grounded quarter-wave antenna. My 10M, 2-element beam had such a feature that was tuned with the aid of an SWR bridge. Today, a vector network analyzer is the instrument of choice and can cost less than a good SWR meter. After getting close on the bench, you can confirm on the airplane to see if 'tweeking' is called for. I've had readers assemble the Archer wing tip antennas per drawings but found it useful to trim dimensions per measured results. Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" ________________________________ Message 5 _____________________________________ Time: 08:57:19 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Archer style wingtip antenna fabrication questions At 04:01 PM 6/22/2021, you wrote: > > >Your ebay-Foo is obviously better than mine; all the hits I got were >for much thicker stuff. > >Thanks for the link! I've got some fiber reinforced pvc sheet that would be suitable for your needs. Drop me a mailing address and I'll send you some scraps to play with. Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" ------------------------------------------------------------------------------------- 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.