spray paint and RF reflections? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: January 07, 2021, 09:10:54 pm
content: Does anyone know any problems related to spray paint and RF? I mean non obviously metallic paint, in normal colors of the rainbow.I made an offset for an antenna positioner using a PVC pipe, but it is ugly and I would like to paint it. Are there any additives that may be invisible to the naked eye that are commonly used with rustoleum paints and mess with microwaves ? I figure hammertone and other obviously metallic paints might cause problems.. but something like yellow? ( I want high visibility colors)

author: HB9EVI
author_rank: Frequent Contributor
timestamp: January 07, 2021, 09:54:38 pm
content: it's possible that also non-metallic paint contains metallic pigments, so it's a kind of lottery; I use rubber paint to protect non-metallic components of my antennas; there where RF flows I use Spinner Plast 2000

author: Lord of nothing
author_rank: Super Contributor
timestamp: January 07, 2021, 10:28:46 pm
content: how about such a foil?https://multimedia.3m.com/mws/media/738952O/farbkarte-3m-wrap-folie-serie-1080.pdf1080-M26 Matte Military Green1080-SB26 Shadow Military GreenThanks

author: coppercone2
author_rank: Super Contributor
timestamp: January 08, 2021, 01:04:16 am
content: yea film/foils are a good option but I have paint on the shelf. I assume they are only dyed, not pigmented, because they are very light in comparison to paint, but I prefer paints durability/clear coat

author: Lord of nothing
author_rank: Super Contributor
timestamp: January 08, 2021, 01:24:29 am
content: well i would be happy if i can use some camo paint to.for example:https://www.obi.at/metallschutzlacke/hammerite-metall-schutzlack-spray-dunkelgruen-hammerschlag-400-ml/p/7388358

author: coppercone2
author_rank: Super Contributor
timestamp: January 08, 2021, 01:37:41 am
content: the idea is that you don't bump into it (my recommendation for lab equipment)

author: coppercone2
author_rank: Super Contributor
timestamp: January 08, 2021, 03:29:46 pm
content: I thought a cheap easy test might be to paint the inside of a pizza box and try to use it as a right angle reflector on some sort of antenna to see if you can get directional gain increase but it seems wonkyhttps://www.rfcafe.com/references/qst/square-corner-reflector-beam-antenna-qst-november-1940.htmhow do you qual something like this? mast qualificationI have made a ball e-field probe before, so paint + box + ball probe seems reminiscent of basic electrophysics faradaish type problems. never thought I would think of that again

author: SeanB
author_rank: Super Contributor
timestamp: January 08, 2021, 03:53:57 pm
content: Pretty much you will find that browns and reds are iron oxides, which are ferromagnetic to some extent, along with black. Simplest test is to take a signal generator, attach a coil that will resonate at your band of choice to it using a highish value resistor, and see how much various spray paints absorb, basically a glorified grid dip meter to see which are the most lossy. But thin coats will not absorb much, so just do a few thin coats, and use a white primer if possible, as that uses titanium dioxide, which RF wise is not too bad. We used to spray radomes with a base coat of grey primer, then 3 coats of dark earth, or leave them primer only, depending on the aircraft and the colour scheme in use. Some went half brown and half sky blue, if the scheme was divided that way, and the 2kW transmit pulse barely noticed the change, not did they heat up any more than air friction did to them. EWS antennas though stayed the same black epoxy finish that came from the factory, no paint allowed, but that was more to them also incorporating IR detectors as well as Rf detectors. Passive systems, but a missile puts out a pretty big IR signature from the motor.

author: coppercone2
author_rank: Super Contributor
timestamp: January 08, 2021, 04:15:20 pm
content: it sounds like a rad-dome would increase in SWR if it was coated by a partial reflector and you would notice it right? (before and after paint test). I am a little worried the military just allows a little bit of deviation since the camouflage is probobly the most important thing over there, especially in south africa because I assume the technology level used in combat is a little low so the naked eye might be the most dangerous thing? I.e. some F22 air superiority fighter might take it into much higher consideration then a burley general purpose african continent war plane? Not sure if those enemies are sporting the latest russian missile defense hardware. I don't want to degrade my lab equipment if possible because of military considerations. Not that any of this likely matters or can be measured easily anywayI bought an acrylic cast rod to be sure, since the electrical conduit I am using is dubious as well. I ended up making alot of parts out of stainless steel on the base and polished them nicely so it stands out well. Not sure if I need a highly visible rod anymore. The system cost/quality is high enough that it does not make sense to cheap out there anymore.I can wrap it carefully in a wide strip (3 inch) of kapton tape and it will look great I think with a few rings around it, like a glass wasp. Or maybe I can find translucent colored heat shrink, or put clear heat shrink over the kapton stripes.I assume the EWS is high powered directional antenna? much more so then radar?

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: January 08, 2021, 10:10:38 pm
content: What kind of frequencies are we talking about here? And what sort of dimensional relationship between the width of the paint exposure to the wavelength? I'm having trouble imagining what your setup looks like, but if the painted surface is a small area relative to wavelength, it may not matter. Sorry if that sounds rudimentary; you probably already know that. I'm just curious.

author: coppercone2
author_rank: Super Contributor
timestamp: January 09, 2021, 12:03:32 am
content: 1 inch pipe 3 feet long for uses yet unknownfrequency limits and bounds are related to my budget and possibly mechanical skills

author: CJay
author_rank: Super Contributor
timestamp: January 09, 2021, 03:38:56 am
content: Standard tip for checking compatibilty of materials for use on radio gear is to whack it into a domestic microwave for a few seconds and see if it gets warm, if it does then something is absorbing the RF energy.

author: coppercone2
author_rank: Super Contributor
timestamp: January 09, 2021, 06:02:00 pm
content: so that is true for suceptors but how about reflectors? I thought they just block power transfer to the food and I guess increases VSWR of the microwave oven (would it not be a fun thing to modify the waveguide in a big microwave to connect to a VSWR meter?) but I am not sure honestly . I read in microwave cooking some stuff comes with reflectors in specific places to reduce their direct heating and I guess let them absorb heat through conduction from things that are radiatively heated or through vapor transfer and foils so the dish is heated correctly without burning. I assume this has something to do with pies but I am not sure, I never tried advanced microwave cooking. Some people online say if you have the correct geometry of non cornea dishcharge? friendly metal profiles it just does not heat food and basically cloaks the food from the microwave energy.So perhaps you can paint a unfriendly pattern in paint which is likely to start arcing to test for conductors?It also seems to relate to microwave kiln work, where you need a strong suceptor to work as a crucible in order to melt metal I believe.The idea I had is that the mast can act as a reflector and cause additional multipath. Say it sticks out under a box covered with RF absorption cones targeting a antenna with a backdrop of more absorption cones. I found when I got above say 6GHz the room was being crazy with the spectrum analyzer dialed.

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: January 09, 2021, 06:41:50 pm
content: Years ago I put a motorised satellite TV dish on my house - one so large it needed planning permission. The local government thought about it a bit, and finally came to a decision of the kind which showed they were going to exercise their powers. They said I could install it if and only if I painted it the same colour as the brickwork of my (1920s UK) house. It duly got painted and worked just fine.Actually there is a story to go with this. I told the installer that I needed it painted. After he realised it wasn't a wind-up, he agreed to do it, and suggested I take a spare brick into his shop so he could see what color was needed. I duly went into the shop with a brick. he wasn't there, his assistant was. He was seriously worried by some random guy he had never seen before marching into the shop carrying a brick. If had had a panic button - he would have hit it. After I explained things to him, his next reaction was that I must the manager's mate, playing a joke on him. It took a while to get him to take me seriously.

author: coppercone2
author_rank: Super Contributor
timestamp: January 09, 2021, 11:10:14 pm
content: lolI kinda wanna paint and get one to a nice automotive finish.does anyone know a brand of nice general purpose parabolic reflectors that can be used with custom horn designs etc?