---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 06/21/18: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:23 AM - Re: Paint question (Robert L. Nuckolls, III) 2. 09:00 AM - Re: Paint question (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 08:23:38 AM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: Paint question At 11:54 AM 6/20/2018, you wrote: >Bob, > >You=99ll like the antenna you have pictured, I >believe.=C2 I have been using a home-brewed >version of that antenna now for several years >and I love it as a dual-band antenna. Pleased to hear it. I've been aware of this design for some years but never had an opportunity/need to try it. Some of our local volunteer fire crews are interested in outdoor antennas for their radios that will cover both the MURS/GMRS frequencies which are, like 2M/70CM, harmonically related. Best yet, this is an antenna they can build themselves. Basic cut, drill, thread and assemble. I don't have to get into the hammer-n-tongs loop! Bob . . . ________________________________ Message 2 _____________________________________ Time: 09:00:42 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Paint question At 09:46 AM 6/20/2018, you wrote: >At 07:56 AM 6/20/2018, you wrote: >>Hi Bob, >>Long time no contact... I=99m happy you=99re still in this game! >> >>Regarding this topic, I wonder how much the the >>conductive bits are in contact with each other. >>I don=99t know how isolated each bit of >>conductive material is in such a paint, but I >>could imagine there could be billions of >>contacts between neighboring bits of flake or >>powder such that there would be a random >>resistive path across the painted surface. I've been doing some 'asphalt contemplation' on a simple test setup to evaluate the effects of various paints/coatings on antenna performance. I was trying to imagine how conductive particles suspended in a non-conductive 'solution' would achieve a microscopic version of the gas-tight contact needed for reliable connection between conductors. It seems that surface tension would cause each particle to be totally enveloped, thus prevented from making physical contact with other particles. Not sure about what happens as the solution becomes a solid when solvents evaporate and the paint dries. I've seen volume resistivity measurements on some coatings/fillers, like potting compounds. These are always VERY high . . . including those designed for thermal conductivity. I'm thinking that there are three potential effects of paint . . . the dielectric effects you hypothesized which would probably be limited to a lowering of resonant frequency, the shielding effects which block and or re-direct the wave fronts of interest and attenuation/dissipation effects that simply turn the RF energy into heat. I'm recalling a bit of a fire drill on the ELT transmitters for Beechjets where a new version of the ELT kept tripping off due to high SWR on the VHF antenna. Seems the older version happily existed with a pair of antennas tucked under the fairing at the root of vertical fin leading edge. Emacs! Oookkaaay . . . Now, let's lay the VHF antenna back so that it sorta conforms to the inside of the fairing . . . except . . . Fairing was also part of an air-intake ductwork for the A/C . . . so the antennas wound up looking like this: Emacs! There were metallic braces inside the fairing along with bond straps that tied the braces to airframe . . . for lighting effects. Added on top of all this was a composite fairing material . . . capped off with paint often chosen by the customer hence of uncontrolled pedigree. What's a poor ELT transmitter to do? Emacs! I couldn't find anywhere in the archives where this installation had been measured for performance . . . a condition that didn't raise its ugly head until a new ELT complained about an 'unsatisfactory' antenna. I suggested we design a new, top loaded vertical for the VHF antenna that remained vertical with better separation from the effects of overhead structures. Emacs! Further, we could fine tune the antenna to accommodate any residual effects from proximity of other structures. This got the flying fuzz all in a dither . . . a new antenna would violate the TSO on the ELT . . . but abusing the TSO'd antenna did not . . . go figure. I think they wound up widening the SWR trip tolerances on the ELT transmitter. Not one of my happier experiences with the bureaucracy. 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.