---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 06/20/18: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:02 AM - Re: Paint question (Stuart Hutchison) 2. 05:57 AM - Re: Paint question (Matt Prather) 3. 07:47 AM - Re: Paint question (Robert L. Nuckolls, III) 4. 09:56 AM - Re: Paint question (Harry Bartel) 5. 07:56 PM - Re: B&C switches (blues750) ________________________________ Message 1 _____________________________________ Time: 04:02:59 AM PST US From: Stuart Hutchison Subject: Re: AeroElectric-List: Paint question G=99day Bob. I=99m building a 200KTAS aeroplane, so very reluctant to put anything out in the breeze that I don=99t have to. I mounted my Garmin and Dynon GPS antennas under the windscreen, but being white they will surely cause unwanted reflections. I intend to test some different things, but first option was to tack some black stockings under the dash mat and slip that over both antennas. I suppose black stockings are darkened with carbon, so there may be some attenuation, but if there is it should be immediately visible on the signal strength bar graphs on screen. Alternatives are black tissue paper and a very light coat of matt black paint as a last resort. It might take me a few weeks to muster the courage to walk in store to buy black stockings, but will come back the forum with some observations soon. Kind regards, Stu > On 20 Jun 2018, at 04:03, Robert L. Nuckolls, III wrote: > >> I hate paint, and I'm certainly no expert. But I'd bet that the only paints that contain enough metal to be an RF issue would be the 'silver' step of fabric coatings, some of which (likely all the old stuff) contain aluminum dust as a UV blocker, and paints specifically sold as metallic and/or metalflake colors. > > > I am skeptical of the claimed effects for metallic > particles in the paint. Intuitively, one can easily > accept that placing conductive/refractive materials > in the path of an electromagnetic wave will have > some 'effect' . . . but to what degree? > > In electromagnetic compatibility schools we're taught > that 'breaks in shields should be kept to 1/10th > wavelength at frequency of interest to avoid degrading > that shield's effectiveness'. > > We've seen reflectors for centimeter wave, dish > antennas made from metallic mesh with significant > openings . . . yet so small compared to the wavelength > of the operating frequency as to behave as a solid > surface. > > When you place a conductor (like a dipole antenna) > out in the air and exposed it to some EM field, > then energy at the frequency where the antenna is > resonant will excite the antenna and manifest with > a strong current node in the middle and voltage nodes > at the ends. > > Now, you've got the 1/2 wave piece of wire 'singing' > in harmony with the constellations of energy that > are harmonic multiples of the resonant frequency. > > What happens to that energy? If you've got a feeding > attached at the current node, you can suck of a substantial > part of that energy and route it someplace else . . . like > your VOR receiver. > > But unless there is a feed line, energy exciting > the antenna will be rejected as heat from ohmic > losses at the current node or re-radiated. After > all, it HAS to go somewhere. > > So what about those little bits of metal suspended in > an otherwise non-conductive paint? I suspect that a > really 'chunky' filling (0.001") flakes would be > the largest practical filler. What portion of a wavelength > is 0.001" compared to the wavelength of the comm > transceiver or even GPS? > > Pretty small. This suggests that the currents induced > in such particles at our frequencies of interest are > vanishingly small, i.e. insignificant. These particles > ARE significant at wavelengths of light, hence effective > modifiers for those electromagnetic fields. However, > I suspect that there are no measurable effects for such > particles at our frequencies of interest. > > Particle sizes are simply too far removed from resonance where > significant currents would be induced. No current, > no heat, no re-radiation, no measurable effects. > > It's an easy experiment to conduct and I have the equipment > to do it . . . just no time at the moment and I'll need > to acquire some exemplar coatings to test. > > If anyone is aware of quantified studies conducted on > this topic, I'd be grateful for some linkage. Anyone > conversant in an alternative explanation is encouraged > to correct my mis-conception . . . > > > Bob . . . > ________________________________ Message 2 _____________________________________ Time: 05:57:35 AM PST US From: Matt Prather Subject: Re: AeroElectric-List: Paint question 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 conta ct 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 b e a random resistive path across the painted surface. So, maybe it=99 s not a constellation of very small dipoles, but a very large, random, resis tive network? Maybe that=99s an easy theory to test - use an ohmmeter to check how much conductivity there is across a painted surface? Might ha ve to dig the probes around to get contact? As far as non-metallic paint on antennas, I wonder if that=99s a detun ing effect because of changing the dielectric... Regards, Matt Prather Sent from my iPhone > On Jun 19, 2018, at 12:56 PM, Ernest Christley wrote: > > If I'm not mistaken, Jim Weir did these experiments and documented them in his antennae booklet. I may be wrong, since it was years ago that I went t hrough them, but I'm pretty sure that he even included a diagram. > > > > On Tuesday, June 19, 2018 2:05 PM, "Robert L. Nuckolls, III" wrote: > > >> I hate paint, and I'm certainly no expert. But I'd bet that the only pain ts that contain enough metal to be an RF issue would be the 'silver' step of fabric coatings, some of which (likely all the old stuff) contain aluminum d ust as a UV blocker, and paints specifically sold as metallic and/or metalfl ake colors. > > > I am skeptical of the claimed effects for metallic > particles in the paint. Intuitively, one can easily > accept that placing conductive/refractive materials > in the path of an electromagnetic wave will have > some 'effect' . . . but to what degree? > > In electromagnetic compatibility schools we're taught > that 'breaks in shields should be kept to 1/10th > wavelength at frequency of interest to avoid degrading > that shield's effectiveness'. > > We've seen reflectors for centimeter wave, dish > antennas made from metallic mesh with significant > openings . . . yet so small compared to the wavelength > of the operating frequency as to behave as a solid > surface. > > When you place a conductor (like a dipole antenna) > out in the air and exposed it to some EM field, > then energy at the frequency where the antenna is > resonant will excite the antenna and manifest with > a strong current node in the middle and voltage nodes > at the ends. > > Now, you've got the 1/2 wave piece of wire 'singing' > in harmony with the constellations of energy that > are harmonic multiples of the resonant frequency. > > What happens to that energy? If you've got a feeding > attached at the current node, you can suck of a substantial > part of that energy and route it someplace else . . . like > your VOR receiver. > > But unless there is a feed line, energy exciting > the antenna will be rejected as heat from ohmic > losses at the current node or re-radiated. After > all, it HAS to go somewhere. > > So what about those little bits of metal suspended in > an otherwise non-conductive paint? I suspect that a > really 'chunky' filling (0.001") flakes would be > the largest practical filler. What portion of a wavelength > is 0.001" compared to the wavelength of the comm > transceiver or even GPS? > > Pretty small. This suggests that the currents induced > in such particles at our frequencies of interest are > vanishingly small, i.e. insignificant. These particles > ARE significant at wavelengths of light, hence effective > modifiers for those electromagnetic fields. However, > I suspect that there are no measurable effects for such > particles at our frequencies of interest. > > Particle sizes are simply too far removed from resonance where > significant currents would be induced. No current, > no heat, no re-radiation, no measurable effects. > > It's an easy experiment to conduct and I have the equipment > to do it . . . just no time at the moment and I'll need > to acquire some exemplar coatings to test. > > If anyone is aware of quantified studies conducted on > this topic, I'd be grateful for some linkage. Anyone > conversant in an alternative explanation is encouraged > to correct my mis-conception . . . > > Bob . . . > > ________________________________ Message 3 _____________________________________ Time: 07:47:20 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Paint question 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. So, >maybe it=99s not a constellation of very small >dipoles, but a very large, random, resistive >network? Maybe that=99s an easy theory to test >- use an ohmmeter to check how much conductivity >there is across a painted surface? Might have >to dig the probes around to get contact? Interesting hypothesis . . . I'm day-dreaming a methodology for testing various coatings as 'shields' . . . >As far as non-metallic paint on antennas, I >wonder if that=99s a detuning effect because of changing the dielectric... A valid hypothesis I think. I've been supplying antennas to folks in the local prescribed burn and fire fighting associations. There's a product sold on eBay fabricated from 'ladder line' that performs as a dual band (VHF/UHF) antenna. I housed one in a piece of 1" thinwall pvc but disappointed to find that the center frequencies moved down about 10%. The antenna was 'snug' in the pipl. Tried a piece of 2" and things got better . . . ~5% downshift. Hmmm . . . getting ready to try a 3" piece with spacers designed to hold the antenna central to the radome. I'm betting this is going to be 'the answer' but not the solution. Wind-loading for so large a radome complicates the support structures. I can use this antenna on the little antenna farm on my roof but not on top of a 30 foot mast in the Kansas winter ice and all the time winds. I've ordered materials to built all metal dual band antennas of this configuration. Emacs! No radome necessary. So I think your dielectric proximity idea is not without merit . . . Bob . . . ________________________________ Message 4 _____________________________________ Time: 09:56:56 AM PST US From: "Harry Bartel" Subject: RE: AeroElectric-List: Paint question Bob, You=99ll like the antenna you have pictured, I believe. I have been using a home-brewed version of that antenna now for several years and I love it as a dual-band antenna. Harry N0HQG From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L. Nuckolls, III Sent: Wednesday, June 20, 2018 9:46 AM Subject: Re: AeroElectric-List: Paint question At 07:56 AM 6/20/2018, you wrote: Hi Bob, Long time no contact... I=C3=A2=82=AC=84=A2m happy you=C3=A2=82=AC=84=A2re still in this game! Regarding this topic, I wonder how much the the conductive bits are in contact with each other. I don=C3=A2=82=AC=84=A2t 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. So, maybe it=C3=A2=82=AC=84=A2s not a constellation of very small dipoles, but a very large, random, resistive network? Maybe that=C3=A2=82=AC=84=A2s an easy theory to test - use an ohmmeter to check how much conductivity there is across a painted surface? Might have to dig the probes around to get contact? Interesting hypothesis . . . I'm day-dreaming a methodology for testing various coatings as 'shields' . . . As far as non-metallic paint on antennas, I wonder if that=C3=A2=82=AC=84=A2s a detuning effect because of changing the dielectric... A valid hypothesis I think. I've been supplying antennas to folks in the local prescribed burn and fire fighting associations. There's a product sold on eBay fabricated from 'ladder line' that performs as a dual band (VHF/UHF) antenna. I housed one in a piece of 1" thinwall pvc but disappointed to find that the center frequencies moved down about 10%. The antenna was 'snug' in the pipl. Tried a piece of 2" and things got better . . . ~5% downshift. Hmmm . . . getting ready to try a 3" piece with spacers designed to hold the antenna central to the radome. I'm betting this is going to be 'the answer' but not the solution. Wind-loading for so large a radome complicates the support structures. I can use this antenna on the little antenna farm on my roof but not on top of a 30 foot mast in the Kansas winter ice and all the time winds. I've ordered materials to built all metal dual band antennas of this configuration. Emacs! No radome necessary. So I think your dielectric proximity idea is not without merit . . . Bob . . . ________________________________ Message 5 _____________________________________ Time: 07:56:49 PM PST US Subject: AeroElectric-List: Re: B&C switches From: "blues750" nuckolls.bob(at)aeroelect wrote: > Dave, > > the MANL limiters came in and then I discovered > that the holder bases I had left over were mis-drilled > and should have been scrapped. Made some new > ones today. Your Care Package is in the mail > tomorrow. > > > Bob . . . Hi Bob...care package received. I really like the form factor of the MANL block, nice and compact!! Very much appreciate your generosity of time, efforts and expertise with all this. I'll be sure to put a little extra into the annual fund raising drive to the boards. Cheers...Dave Read this topic online here: http://forums.matronics.com/viewtopic.php?p=481052#481052 ------------------------------------------------------------------------------------- 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.