RF interference from 'metallic' paints.

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Chris_H

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This question has been in my mind for a while, I have read what I can find on this forum and elsewhere. I am wondering about RF interference from 'metal flake' paint jobs on a rocket. The metallic flakes I want to use are actually polyester, with very little metal. There are paints with significant metal content, but that is not what I am asking about. I pulled out a test panel of the flakes in question, sprayed heavily on a piece of foam core, and alternated readings with a 216 mhz Marshall Telemetry tracker from a distance of about 300'. I could not detect any difference between the transmitter being covered by the large panel, or not.

I see that forum member Nathan has a beautiful rocket painted in a metallic blue. His is probably the same type of flake, but smaller. Some of the smaller flake metallics are real powdered aluminum. I have seen other rockets, as well, painted in metallics, and one in what looks to be a chrome finish.

I want to do a candy apple red with flames on a rocket project, and can figure out a plan to leave the portion where the GPS is, uncovered with flake, but would prefer to carry the flake up higher. The GPS is using 433mhz, if that makes a difference.

I would like to hear voices with experience of either failures, or rockets that have no issues with metallic paint jobs.

A couple of potential benefits in a metallic paint could be more reflectivity of the sun to keep the electronics cooler in the sun, and possibly in creating a big reflector in the sky for visual tracking if the light is right. Plus, it looks super cool.

Is there a significant difference between how a 216mhz frequency is going to behave in passing through something, vs a 433mhz frequency? I have still not yet taken my HAM exam, so cannot yet fire up the GPS transmitter to test that unit behind the test panel.

What about the frequency used by the GPS antenna? (Aim Xtra)


Bad idea? Or maybe it flies?

Cheers!
 
Chris,

Some clarification. What you are talking about here isn't interference from the metallic paint but rather attenuation. If you paint a payload bay, nose cone, etc. with a metallic paint and surround the tracker with that paint you're basically creating a Faraday Cage. It's not a perfect shielded enclosure, so some of the signal will escape to be received.

The degree of attenuation of the signal will be influenced by a number of factors.

Frequency is one of them, as you guessed, and it's critical. A 433 MHz tracker would almost certainly suffer more from the attenuation of the metallic paint.
Power is another factor, so a more powerful tracker will fare better than one that is low power. So a 700 millwatt tracker will work better than a 100 milliwatt tracker.

When it comes to GPS design, two frequencies are utilized; one at 1575.42 MHz (10.23 MHz × 154) called L1; and a second at 1227.60 MHz (10.23 MHz × 120), called L2. The C/A code is transmitted on the L1 frequency as a 1.023 MHz signal using a bi-phase shift keying (BPSK) modulation technique. So the attenuation of metallic paint will be much more harmful here than at 433 mhz. You're not transmitting GPS information, you're receiving it from the satellites, but the attenuation affects reception as well as transmission.

Much like doing a Dual Deploy Ground Test, the only way to be certain is to test it. The test you performed isn't valid--because you're not encasing the tracker or GPS receiver in an enclosure. You would be better off to build a "box" using either fiberglass, cardboard, etc. and paint that with the metallic paint--and test reception/transmission.

Hope that makes sense. Feel free to ask additional questions.
 
My level 3 had a Altus Metrum and copious amounts of Rustolium metallic aluminum paint, I lost tracking at about 4000' and didn't pick it up until I was within a 1/2 mile of the rockets landing spot. But it landed in a dried up evaporation pond amidst a lot of vegetation. It was below ground level covered in weeds. However I have launched rockets above 6000 feet with the Altus Metrum with no loss of comms.
 
Thank you.

I just looked into Rustoleum metallics, and they mention 'real interlocking metal flakes'. I know that some of the fine metallics use real metal, powdered aluminum. The flake I am talking about is like 'bass boat' flake, and is polyester, perhaps metallized some how. I am also trying to get an answer as to exactly how this flake is made, and what it's actual metal content is.

Will silver mylar also attenuate RF signals?
 
Thank you. That thread also discusses Rustoleum, and 'One Shot' which is a really cool paint for getting coverage in one coat, it is for sign painting, and I know it contains real metal.

Here are the flakes I am speaking of. And no, I probably would not pay that much for flake just for a rocket. I have many years of professional painting experience, so this is already in my kit.


Chris,

Here's a thread from the RC domain that may be of interest:

https://www.rcuniverse.com/forum/kit-building-121/10392029-metallic-paint-radio-interference.html


Les,

Doesn't a faraday cage require continuous conductivity over the entire plane of the cage for it to be effective? I guess the follow-on question is, does metallic flake paint create a conductive plane, or does it just "look" like it does?

-Robert
 
Robert,

Yes, that's why it wouldn't be accurate to refer to a metallic painted nose cone or payload bay as a Faraday cage. It's actually a pretty poorly shielded RF enclosure. On a payload bay, it's actually open to radio signals on both ends. With a nose cone, it's closer to be a true Faraday Cage.

My concern was that Chris was attempting to test by holding up a "wall" of a painted wall of foam core, which is not even close to accurately simulating the environment. The fact is that receiving RF from a rocket is problematic under ideal conditions. You have a low power transmitter, with a poor antenna transmitting from a rapidly moving vehicle that can move in multiple directions at the same time (pitch, yaw, roll, etc.)

All of these movements affect polarity of the transmitted signal, and at VHF/UHF frequencies, these polarization changes can reduce the signal by as much as 20db or even more. If you compound that by putting that transmitter inside a RF shielded enclosure, you're asking for trouble.

I too love metallic paint on rockets. I'm painting one right now--but I chose to paint the fin can and nose cone gloss black specifically so that I could fly a GPS receiver and 433 Mhz tracker in the nose cone. Your milage may vary.

Test it and see. The "bass boat" flakes may be another material that will offer less attenuation. If you find something that works, share it with the forum. I'd love to find a solution that doesn't dictate my paint choices.
 
One of the potential 'work arounds' is to start at the tip with a bright yellow, and the metal flake is only in the flames, starting a little lower. That would give at least some of the enclosure an 'opening'

I am going to do some testing, and will find out, as these paint options are just too pretty.
 
Chris,
When it comes to GPS design, two frequencies are utilized; one at 1575.42 MHz (10.23 MHz × 154) called L1; and a second at 1227.60 MHz (10.23 MHz × 120), called L2. The C/A code is transmitted on the L1 frequency as a 1.023 MHz signal using a bi-phase shift keying (BPSK) modulation technique. So the attenuation of metallic paint will be much more harmful here than at 433 mhz. You're not transmitting GPS information, you're receiving it from the satellites, but the attenuation affects reception as well as transmission.

From this description, it seems like testing the GPS reception and how long it takes to get a location might be a better test than testing the reception from the rocket transmitter. Of course a signal strength meter on the receiver should show the difference between the transmitted signal in free air and in a painted enclosure much better.
 
The attenuation is frequency and power dependent. I'll vouch for the fact that the Rust-Oleum metallic will shield a low-powered beeline GPS tracker on 70 centimeters. In 2008 I launched two Rockets one right after the other, one was cardboard and and the other was fiberglass. They both were painted with Rust-Oleum metallic flake paint, right out of the can. The cardboard rocket went to 3000 feet and was lost for a week. The fiberglass rocket went to 10,000 ft and only one position packet was received at 5200 feet. It fortunately was recovered within the limits of sight and returned that day.
The other kicker here is when I recovered the fiberglass rocket that went to 10,000 ft, I knew I had the beeline GPS set to shut off the battery when it got too low. I just put the rocket in the back seat of the car and took off to the pizza joint the group went after the launch. I then drove the 44 miles home took the rocket apart and just for the heck of it tried to download a KML file. To my abject surprise I had a valid position file on the beeline GPS tracker that had a 6 to 11 satellite lock for most of the flight. When I plugged it in to Google Earth it even receive some positions while the car was in the parking lot of the pizza place. Also had some positions on the way home until the battery Auto shut-off. It seemed that the GPS signals passed right through the metallic paint. The RF couldn't get out of the eBay. Stupidhead did not do very good range test back then

I say to avoid metallic paints on a tracker carrier. For instance, stuff the tracker in a nose cone carrier and paint the nosecone a non-metallic color and your rocket can be any metallic color you want.

Some say they get away with metallics with 900 megahertz trackers. I say I'd like to see if they affected recoveries of completely metallically painted Rockets that were totally sight unseen.

Short answer: Avoid metallic paints with RF trackers. Long answer: Test like crazy. Would be a shame to do a beautiful metallic paint job on a rocket and find out your tracker isn't worth diddly-squat. Been there, done that. Don't repeat my mistakes. Kurt
 
Guess I'm the odd man out.
I have several rockets painted with Rusto metallic blue & silver & black.
Never had an issue with signal using Tela & Comm-Spec & Marshall.

SpaceCowboy 54mm & 75mm [silver/blue]
DarkStar 3 [black]
Darkstar 4 [silver/blue]
WildMan 3 [silver/blue]
 
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If you have enough excess signal in the link budget you will never know how much margin you have until you start losing data packets.

Here is a thought. There was another thread where someone talked about cutting a slot in a CF airframe (making a slot antenna effectively) to allow the signals in and out. Was it from Jim Jarvis maybe? Anyway, how about coating it black as the first coat (non-metallic) and then paint the metallic over the top with some black stripes masked around the airframe for a nice pattern effect. They would also be windows to the world for the radio system :wink: .
 
Guess I'm the odd man out.
I have several rockets painted with Rusto metallic blue & silver & black.
Never had an issue with signal using Tela & Comm-Spec & Marshall.

SpaceCowboy 54mm & 75mm [silver/blue]
DarkStar 3 [black]
Darkstar 4 [silver/blue]
WildMan 3 [silver/blue]

All 200Mhz trackers some of which are 50 mW of power output. All I'm say'in is walking to the Launchpad 400 feet away is not an adequate range test. Attenuation is frequency and power output dependent. Kurt
 
If you have enough excess signal in the link budget you will never know how much margin you have until you start losing data packets

This ^^^

It's been said that "Engineering is the art of 'good enough'". You may find that your packet reception at 5,000' is "good enough", but at 10,000' or 20,000' it is not. Unless you have the proper equipment to test (and unless you do FCC certifications it's unlikely that you do) it's very difficult to predict exactly what is "good enough". For that reason, we recommend against doing things that you KNOW will reduce the link budget... metallic paints, carbon fiber in the transmitter bay, and allthreads running parallel to the antenna. Based on my personal experience, I would put an Eggfinder in an AV bay with allthreads if I was going to 5,000', but no way if it was 10,000'. I like to get my rockets back.
 
In amateur radio, people always seem to be looking for ways to cheat physics. Especially in the realm of antennas. Any number of attempts are made to reduce the size of antennas, without sacrificing performance. Any manner of wild claims are made. But I like to say, "Physics don't give a damn."

Generally speaking, if you want an antenna to perform better, it has to be bigger.

Have you seen the packages for GMRS/FRS Walkie Talkies that claims "Up to ten miles of range!" or "Up to twenty miles of range." Nonsense...same restrictions on power, same poor antennas = same performance. But if you go up high on two mountain peaks that have Line-of-Sight with each other, you might get crazy range. Just don't try getting that kind of performance in an amusement park, or your neighborhood.

Rockets are are notoriously difficult environment to operate RF from. The history of post-war rocketry is filled with efforts to improve telemetry, and manned mission communications.

Best practice would be not to handicap yourself by putting a tracker or GPS receiver inside an AV Bay painted with metallic paint.

And as an engineer friend of mine likes to say, "There is no such thing as an excess link budget."
 
Thank you, all. I really appreciate this discussion. I was hoping to hear some knowledge of a difference between some metallic paints, some of them having insignificant, or even no real metal content. I have not yet called the manufacturer, as I have not had time to sit on hold, yet. I know some have real metal, and that is the source of the metallic effect. I think that some of the holographic flakes may not have any metal at all, but I am not sure. The rocket in question is more on the novelty scale, but not quite. It is probably capable of flying to over 11,000'. It is a rocket, though, and pretty paint is not the goal, it would just be fun. I never was afraid to put a killer paint job on something like a bike, for instance, rub it out perfect, and then go toss it down a hill, scratch it on rocks, etc. The idea of putting a $1000 paint job on a rocket, and then losing it, well, that is the risk. Losing it from poor engineering in regards to hedging on a link budget does not sound smart, or like something I will do.


In regards to threaded rod near a GPS antenna, have I already made fatal mistakes here in this photo? I had considered putting it in the nose cone, but was already planning on putting a Garmin dog collar up there. The Aim Xtra will be used for one of the deployment devices, in addition to a Marsa 54l. Unless it is a very bad idea next to the threaded rod, and then a rethink will happen.

This is stainless rod, does the type of metal have anything to do with attenuation and RF signals?

 
Chris,

I apologize. The topic strayed into hypothetical areas, when you're just looking for straight answers to meet your need.

Is the antenna going into be inside the AV Bay? I assume so. My advice would be to use a couple of wraps of masking tape to secure the antenna to the fiberglass center tube on the opposite site. This puts it as far away as possible from both electronics and the metal rods.

The type of metal in the rod probably won't affect how it interacts with RF much. Nylon or teflon rods would be the best choice, but might lack the strength required. I think you'll be fine with this setup. Just don't attach that antenna right next to a metal rod.

BTW, both the AV Bay and RF look like good quality engineering. I think you're good to go.
 
No, no apologies necessary at all! I like all of this. I am studying for my HAM test in a couple of weeks, and all of this is super pertinent to rocketry, and beyond. Thank you for your comments. Diverge further if you feel like it.

In this photo, the antenna actually spirals around the motor pass through tube, and mounts through the bulkhead. The cap of the bulkhead is removeable, and there will be a small piece of one more .125" layer of G10 with a 'press fit' for the antenna, that will epoxy to the lid to give further support. The antenna will then have more than 1/4" of press fit support to help guard against any harness lines stressing it too much. I think it will hold. I have played with the geometry, and once it is under tension, the harness might not bug the antenna too much.

The actual GPS antenna is the square thing on the Aim unit itself, but you probably knew that already.

I am in deep, and welcome all the help and advice that I can get.

Not related to electronics, but I plan on using a zip tie passed through both eye nuts after sealing the AV bay, to ensure that any twisting or carrying on during descent does not unscrew the nuts.

Also, I plan on replacing all of the nuts inside the AV bay with nylon nuts. The stainless hardware I had in my stuff, so it is for mock up only. When all the parts are gathered, and fitted, I will glue this thing together.

I do have concern about the GPS antenna being close to the threaded rod in the AV bay. As a noob, I am shooting in the dark with some of this.
 
At 1,200 MHz that GPS antenna is actually several wavelengths away from the metal rods. I don't think that is a concern.

Your plan for the tracker antenna also seems solid from an RF standpoint. I usually mount antennas vertically within the AV Bay or nosecone, and orient my receiver antenna the same. Under boost, and especially during recovery, the polarity of the transmitted signal will vary quite a bit. I usually use a small beam for the receiver, and "rotate" the elements between vertical and horizontal-and points in between to find the best signal.

Once the rocket lands, I usually try to orient the receiver antenna one last time for the strongest signal, and then walk towards the last visual bearing of the rocket. Remember that changes in polarity can degrade the signal by 20db or more. If the rocket lands in the field, and the antenna is laying flat (horizontal) but your receive antenna is vertical, you may not even hear the rocket. Small hills, trees, and other obstructions can cause real problems too.

The dog collar in the nosecone is a great idea for a backup. Good luck on the ham radio test. We need more amateur radio operators like yourself.
 
My Grandfather introduced me to HAM rdio when I was about 14 years old. He taught me about building simple IC projects, and also took me one night for one of those events where HAMS set up and operate a station all night. I also need this tech licensing for the radio I will carry when kayak fishing. He also shared with me a thought that I never forgot, that every home should have a lathe and a mill. I think these are coming to my shop this year, if not, soon. Bridgeport and Hardinge chucker.


There is another potential RF issue with this one, when a 6GXL is in this, the top of the motor casing comes to just above the black switch ring. Not sure how much that will matter though, as it will lose lock as it passes through mach 1, I think? If a Loki L1400 ever goes in this one, the AIM will probably be used as backup only, as it will be pushed up against the motor casing until apogee. The dog collar seems like a good way to go. A couple of other projects that are in the works will be going much higher.

Cool tip about polarity! Thanks.
 
In terms of the 6GXL hardware case, that would concern me more than the rods.

It all depends on the placement of the tracker antenna. I'd opt to mount it on the opposite side of the tube from the GPS/Tracker, and above the black centering ring. That would keep it away from the metal casing, hardware rods, and the GPS/Tracker itself. Once you have pictures of the G-10 sled, I'd love to see those. Always looking for ideas for future projects.

Looks very well build. I admire your rocketry skills.
 
At 1,200 MHz that GPS antenna is actually several wavelengths away from the metal rods. I don't think that is a concern.
I agree. The antenna being obscured by the threaded rods or motor in the central tube are also less of an issue these days as the GPS units have so many correlators and such great algorithms they seem to be able to get lock on some very scratchy Rx signals.
 
My pleasure. I've learned so much for a lot of folks here on TRF. Rarely am I in a position to offer any advice at all--other than "here's how not to do it." Radio I know, rocketry is still very new to me. Best of luck--I'll be waiting to hear how it all turns out.
 
I agree. The antenna being obscured by the threaded rods or motor in the central tube are also less of an issue these days as the GPS units have so many correlators and such great algorithms they seem to be able to get lock on some very scratchy Rx signals.

Ditto, GPS antenna just have facing out the tube. The RF antenna is best in "free air". In my example above in #11 the GPS had no trouble getting a lock from inside a Rustoleum rattle can metallic painted rocket, one cardboard, one fiberglass.
The 400Mhz Rf just couldn't get out. Heck it was one of the few times I got the squirrely G-switch to work right in the Beeline GPS. Other alternative is have a bulkhead mount antenna that goes aft and gets exposed at apogee during deployment or
when I had a beautifully metallically painted Wildman Jr. rocket, after my experience in #11, my plan was to have a fine form fit hole into the upper main chute bay through the bulkhead for the wire antenna to go through and use clay to chaulk the
wire in and use a cardboard stent to keep the wire from getting smushed by the parachute. Problem was the upper tube was the dreaded Red metallic Rustoleum. My remedy was dip the upper tube, (it's a small rocket) in acetone and strip the beautiful red paint off on the upper tube only!! Left the NC and sustainer metallic red. I re-prepped and shot a plain non-metallic bright yellow. Yeah, I know gaudy but out of 14 flights, I've only seen the rocket once coming in under chute and the other 13 times I know it worked because all the laundry is out ever so nicely when I walk up to it. Without the Beeline GPS tracker I would have lost it easily 13 times.

We know RF won't work inside CF and I believe GPS might not either hence the creative cutting to let the Rf "in" and "out". Although I think in some cases this was so a wireless signal could "get in" to activate the deployment electronics.
Easier to simply use a nose mounted tracker in a radio lucent nose cone. Kurt
 
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Other alternative is have a bulkhead mount antenna that goes aft and gets exposed at apogee during deployment Kurt

Do you think that a bulkhead mounted antenna (1/4 wave) that goes up into the fiberglass, standard painted nosecone will work as well as one that goes into free air at apogee?

And if the one that points downward and is exposed at apogee, is laying up alongside a motor during flight, which configuration would you choose for a flight that goes to around 10k'?

This antenna has a natural slight curve to it, it will be mounted towards the edge of the lid, and the main chute will be in a deployment bag that I am making specifically for this rocket and chute, so the antenna should not be squished too badly by the chute. Also, it will be in a heavily fortified mount for the first 1/4". The antenna cable bulkhead fitting will be threaded into the G10, and a little bit of ply with the 1/4-36 threads, leaving enough so that just before the antenna comes tight on the fitting, it contacts plywood first. I think the antenna would have to shear before it was broken off at the fitting.
 
Do you think that a bulkhead mounted antenna (1/4 wave) that goes up into the fiberglass, standard painted nosecone will work as well as one that goes into free air at apogee?

And if the one that points downward and is exposed at apogee, is laying up alongside a motor during flight, which configuration would you choose for a flight that goes to around 10k'?

This antenna has a natural slight curve to it, it will be mounted towards the edge of the lid, and the main chute will be in a deployment bag that I am making specifically for this rocket and chute, so the antenna should not be squished too badly by the chute. Also, it will be in a heavily fortified mount for the first 1/4". The antenna cable bulkhead fitting will be threaded into the G10, and a little bit of ply with the 1/4-36 threads, leaving enough so that just before the antenna comes tight on the fitting, it contacts plywood first. I think the antenna would have to shear before it was broken off at the fitting.

Yup, I cut the base off a molded plastic nosecone, screwed it into a length of tubing to make an ebay in a 38mm minimum diameter rocket.IMG_20170113_063231.jpgIMG_20170113_063212.jpg

IMG_20150214_090634.jpgIMG_20150214_090540.jpgIMG_20150214_090500.jpgIMG_20150214_090336.jpgIMG_20150214_090318.jpgmd4.jpgmd3.jpgIMG_20141217_185717.jpg

Like the above project. Works fine.

Now the backward facing antenna I'm talking about in the ebay of a DD rocket that I painted with metallic and wanted to salvage it for flight. The Beeline would ride in the aft portion with the altimeters up above. The antenna would be exposed at apogee. Pictures of that one in the next post.
 
Next post:

AntWM3.jpgWM3.jpg

I stretched a Wildman rocket by lengthening the sustainer, upper bay and the coupler ebay. It's the rocket I mentioned went to 10k above except I had the antenna facing forward into the metallic painted main chute compartment.
I was lucky it came down within sight (just barely) and I got it back. The pictures show an aft antenna as a compromise of having the antenna out in the open at least at apogee. The metallic paint didn't block the GPS signal but
the unpainted coupler is where the Beeline GPS would be contained. That is an unproven spring wound antenna I got. I believe this setup would work except I've changed my mind and bought a new nosecone to make for a nose mounted tracker so I can easily fit two deployment devices in the 10 inch long ebay. Rocket is 12 years old and I couldn't fit the Beeline and my two intended deployment devices MAWD, Arts 2 in that bay. I flew it with the MAWD
and the Beeline and for safety's sake, I will never do that again. Tracker nose with two modern more robust deployment devices although my unflown Arts II is likely fine.
And yes.............. That sustainer is long enough for a 54mm Loki M. I have the 4000ns case and an L2050. I don't have an L3 yet so the M1378 is out for now. I'd probably have to go to Cloudbusters to fly this rocket with
the M as it would bust all the nearby waivers closer to me. Kurt
 
Cool. Thanks, Kurt.


Are those LED's in the charge terminals just there for testing the electronics?

Are you planning on stuffing the L2050 into that rocket? Is it a 3" diameter? Even at 3" diameter, wouldn't that configuration be kinda scary with that motor, having 2 breaks above the end of the case on a skinny rocket? I have that 54 / 4000 motor casing, it is one of the things I have been thinking about quite a bit in the past few months, in rocketry projects.
 
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