Radar Reflector

[vontresc]

Anyone here know enough about the ATC radar system to answer this for me? How big would a radar reflector have to be to improve the primary return of my glider? The sailing versions look like they would possibly fit into the fuselage, but I assume that maritime radar uses a different frequency from the ASR that the ATC uses.

 

[jesse]

No clue, I do know that ATC generally has no issue picking up my Flybaby on primary, maybe the cowling and engine help. Probably just all the damn flying wires.

 

[jhausch]

S band: 7.5–15 cm
Moderate range surveillance, Terminal air traffic control, long-range weather, marine radar; 'S' for 'short'

X Band: 2.5–3.75 cm
Missile guidance, marine radar, weather, medium-resolution mapping and ground surveillance; in the USA the narrow range 10.525 GHz ±25 MHz is used for airport radar; short range tracking. Named X band because the frequency was a secret during WW2.

L Band: 15–30 cm
Long range air traffic control and surveillance; 'L' for 'long'

Stolen from here:
http://en.wikipedia.org/wiki/Radar#Frequency_bands

Some of those sailing units fold pretty easily. I wonder if you could unfold one in flight while talking to ATC to see if they see a difference?

Interesting site:
http://www.theradarreflectorsite.org/

 

[Velocity173]

Has ATC said that your aircraft is not visible on radar? If so it might be a LOS issue and not even your aircraft. A transponder would be more important anyway. If a controller is busy they might not even see your primary or even believe it's an aircraft return (birds). Greater chance of getting traffic called on you with a transponder.

 

[vontresc]

They saw me the other day just outside of the Class C, but I was figuring a better return wouldn't be a bad thing.

 

[airguy]

They saw me the other day just outside of the Class C, but I was figuring a better return wouldn't be a bad thing.

Would a small transponder and battery weigh less than the reflector? It would certainly be more useful.

 

[Ted]

Would a small transponder and battery weigh less than the reflector? It would certainly be more useful.

That was my exact thought.

 

[roncachamp]

Anyone here know enough about the ATC radar system to answer this for me? How big would a radar reflector have to be to improve the primary return of my glider? The sailing versions look like they would possibly fit into the fuselage, but I assume that maritime radar uses a different frequency from the ASR that the ATC uses.

Depends on the radar. I'd expect Madison approach to be able to pick you up now, although it may be a weak target. I wouldn't expect Chicago Center to get a usable target from the Horicon ARSR. If you head up north, Minneapolis center won't see you with the Eagle River site no matter how big your reflector is as that's just a beacon interrogator.

 

[vontresc]

Would a small transponder and battery weigh less than the reflector? It would certainly be more useful.

Eventually I'd like to do that. Right now I just don't feel like shelling out $2k+ for a transponder. I was just hoping a sub $100 device would help increasing my visibility.

 

[JimNtexas]

A quarter wavelength of a typical ATC radar is on the order of 3 to 10 cm. So you could put some wires or metal strips in your glider's fuselage cut to lengths in that range, this would increase your radar cross section significantly.

Of course, that only works for primary radar, any facility that ignores or doesn't have primary radar won't see you. Nor will any collision warning system on another airplane.

Wearing a parachute is a good idea. Don't take my word for it, ask the glider pilot mentioned here.

 

[ScottM]

Build a couple of corner reflectors and put them in your fuselage.

 

[weirdjim]

Depends on the radar. I'd expect Madison approach to be able to pick you up now, although it may be a weak target. I wouldn't expect Chicago Center to get a usable target from the Horicon ARSR. If you head up north, Minneapolis center won't see you with the Eagle River site no matter how big your reflector is as that's just a beacon interrogator.

OK, since I don't know, somebody educate me. When ATC is using primary radar to track an aircraft, what frequency are they using. Or do they use different bands for short range terminal and long range enroute radar?

Of COURSE the "primary" radar is currently the 1030/1090 MHz. transponder, but is/are there a true RADAR frequency(ies) in use?

Somebody tell me and I'll calculate the size of the tinfoil strips to paste inside the skin of the glider.

Thanks,

Jim

 

[Ted]

Eventually I'd like to do that. Right now I just don't feel like shelling out $2k+ for a transponder. I was just hoping a sub $100 device would help increasing my visibility.

My personal opinion - when I get told "primary target only" I pretty much view that as useless information and don't spend much time looking for it. I suspect most others are like-minded. If you want to get my attention, add a Mode C transponder. Just save the $100 towards the total cost of the kit.

 

[Art VanDelay]

Okay, you need to make yourself a special tin foil beanie to wear. Then ATC can see you and space aliens and the government can't read your thoughts ! Plus, you'll be styling !

 

[jesse]

My personal opinion - when I get told "primary target only" I pretty much view that as useless information and don't spend much time looking for it. I suspect most others are like-minded. If you want to get my attention, add a Mode C transponder. Just save the $100 towards the total cost of the kit.

Which is why I try to listen to the appropriate ATC facilities when I'm Flybabying. I've spoke up before when they've given someone a primary return traffic warning that I'm pretty damn sure is me.

 

[vontresc]

I was pretty much doing what Jesse said. I did call Madison, when they called me out as slow moving possible bird target.

Now Ted, Just look out of the damn plane You wouldn't want to be run over by some inconsiderate NORDOhole ;-)

 

[Ted]

Now Ted, Just look out of the damn plane You wouldn't want to be run over by some inconsiderate NORDOhole ;-)

Why look out the window when I have all these shiny gadgets to look at?

Seriously, I do make a point of looking out the window when VFR, but it's in all directions. So if I get told "Traffic - 11 o'clock, 1 mile, primary target only" I treat that about as "Spend an extra 2 seconds looking there, then go back to looking elsewhere." Just one perspective on the matter. If I get told an altitude that goes with it, I will absolutely spend more of my time looking out the window in that direction.

Another point to make: In many planes, especially twins, I have virtually no downward visibility for targets that will be nearby. So if I get told 11 o'clock, 1 mile, I can't see you anyway.

 

[Ghery]

I have a folding radar reflector for my boat. There's no way a transponder and battery weigh less than that thing. There's hardly any mass to it at all. Just a few corner reflectors in a single package.

 

[weirdjim]

Another point to make: In many planes, especially twins, I have virtually no downward visibility for targets that will be nearby. So if I get told 11 o'clock, 1 mile, I can't see you anyway.

Why? That is just about 10° left of the nose and can be anywhere from level across to straight up or straight down.

Jim

 

[kontiki]

Maybe use paint with metal pigment? There is shielding paint available, I'm not sure how well it reflects or absorbs.

 

[JimNtexas]

OK, since I don't know, somebody educate me. When ATC is using primary radar to track an aircraft, what frequency are they using. Or do they use different bands for short range terminal and long range enroute radar?

Approach control radars will operate on a higher frequency than enroute (center) radars. The most common terminal area radar is the ASR-11, which operates around 2800mhz.

Center radars are often shared with the military and operate around 1200mhz. The ARSR-4 and similar radars are used for long range surveillance.

 

[comanchepilot]

why not just skip it all and put in an ADS-B transponder . . .

 

[weirdjim]

Approach control radars will operate on a higher frequency than enroute (center) radars. The most common terminal area radar is the ASR-11, which operates around 2800mhz.

Center radars are often shared with the military and operate around 1200mhz. The ARSR-4 and similar radars are used for long range surveillance.

Is that the best we can do? "Around 2.8 GHz."?? How "often" are center radars shared? Again "around 1.2 Ghz." Frankly, I've never seen a dish big enough at a center area to be used at 1.2 Gig, so I'm not convinced that they use a frequency that low.

Anybody KNOW for REAL???

THanks,

Jim

 

[weirdjim]

Maybe use paint with metal pigment? There is shielding paint available, I'm not sure how well it reflects or absorbs.

Paint with metal pigment makes not a whit of difference. For thirty years we've been using internal ("hidden") antennas in Tupperware airplanes with "metal" paint and the skin is absolutely transparent to electromagnetic radiation. Same for silver dope as an undercoat for UV.

Never heard of shielding paint. Care to share?

Jim

 

[Ted]

Why? That is just about 10° left of the nose and can be anywhere from level across to straight up or straight down.

Jim

Your eyes must be better than mine. I've been flying these twins a bit, and have never seen traffic below me between the nose and the engines. Yes, a single will be better in this regard, but I don't recall great luck with low-wing singles, either.

 

[PW_Plack]

A quarter wavelength of a typical ATC radar is on the order of 3 to 10 cm. So you could put some wires or metal strips in your glider's fuselage cut to lengths in that range...

You need a half-wave to resonate, unless you're putting a ground plane under that quarter-wave. If you're cutting foil strips, they'd need to be a half-wave.

Never heard of shielding paint. Care to share?

Regular paint with metallic flakes may not have them close enough together to really conduct. This stuff is good enough to use for a ground plane on a fiberglass surface. The surface resistance gets lower with additional coats. You can mask a specific radius to achieve resonance at a particular frequency, although the coating will be a little lossy, so the peak is not sharp.

Guitar players use that coating to shield the compartment cut out of solid-body guitars to hold switches and level controls, and some report it effective in reducing hum.

 

[Mike5250]

Eventually I'd like to do that. Right now I just don't feel like shelling out $2k+ for a transponder. I was just hoping a sub $100 device would help increasing my visibility.

I'm all for freedom and not being forced to add certain equipment but a transponder should be a requirement. Not fun hearing "traffic 12 o'clock, 2 miles, altitude/type unknown."

 

[weirdjim]

You need a half-wave to resonate, unless you're putting a ground plane under that quarter-wave. If you're cutting foil strips, they'd need to be a half-wave.

Absolutely true. You could also use 3/2 wave if you had the room and wanted a larger aperture.

Regular paint with metallic flakes may not have them close enough together to really conduct. This stuff is good enough to use for a ground plane on a fiberglass surface. The surface resistance gets lower with additional coats. You can mask a specific radius to achieve resonance at a particular frequency, although the coating will be a little lossy, so the peak is not sharp.

Now I learned something. Never knew nickel paint existed. THere are a few places I could have used that stuff over the years. At $36 a can it ain't cheap, but it would have saved me HOURS of dicking around soldering copper tape shielding together.

Thanks for the pointer. jw

.....

 

[jesse]

I'm all for freedom and not being forced to add certain equipment but a transponder should be a requirement. Not fun hearing "traffic 12 o'clock, 2 miles, altitude/type unknown."

Pretty hard for me to justify putting a $3,000 box in a $9,000 airplane.

 

[PW_Plack]

Now I learned something. Never knew nickel paint existed. THere are a few places I could have used that stuff over the years. At $36 a can it ain't cheap, but it would have saved me HOURS of dicking around soldering copper tape shielding together.

It's a neat product, but it has its limitations. It's been a while since I used it, but I think it's spec'd for 5 ohms per square, and I got it down to almost 1 ohm with three coats. But you have to find a way to couple to it in some way that will withstand vibration and dissimilar metal issues over time.

I've never tried to make a dipole with it, but that's a future experiment.

Once you start using the can, they recommend you don't let it sit, and it has something like a one-year shelf life even before it's opened. Once I find enough cool experiments to try, I'll order another can. I want to try painting a vertical dipole inside a fiberglass tail. It might also be possible to mask and spray-on a multi-element resonant radar reflector in a tail, which would be pretty cool.

 

[weirdjim]

I've never tried to make a dipole with it, but that's a future experiment.

I'm trying to imagine something that would connect the coax to the center of the ears.

.....

 

[ClimbnSink]

I'm all for freedom and not being forced to add certain equipment but a transponder should be a requirement. Not fun hearing "traffic 12 o'clock, 2 miles, altitude/type unknown."

Do they make transponder suppositories cause I don't know where else on my paraglider to put one.
Look out the window or die.

 

[JimNtexas]

Is that the best we can do? "Around 2.8 GHz."?? How "often" are center radars shared? Again "around 1.2 Ghz." Frankly, I've never seen a dish big enough at a center area to be used at 1.2 Gig, so I'm not convinced that they use a frequency that low.

I know for real, follow the links I provided.

I don't have the classified schematic of the USAF early warning network right in front of me at this moment, so I can't tell you exactly which radars are shared with the FAA, nor can I recall the exact frequency and prf each military and FAA radar is operating on at this moment, since each installation will have a different frequency (around 1200mhz for long range radars), and the operator can choose the prf.

I can tell you that 'around 1200mzh' is plenty close enough to make a radar reflector. If you want to see an antenna big enough to see airplanes at long range at around 1200mhz you need to crawl into one of those big domes pictured in the link I provided.

 

[Mike5250]

Pretty hard for me to justify putting a $3,000 box in a $9,000 airplane.

Yea makes sense. It looks like experimental transponders are all 2,000++. Bringing the flybaby to osh?

 

[jesse]

Yea makes sense. It looks like experimental transponders are all 2,000++. Bringing the flybaby to osh?

Yeah, it's just difficult to get something that is small enough with low power consumption without paying quite a bit. Both requirements in a Flybaby with no ability to generate power on its own.

I flew it to OSH last year, planning on doing so this year as well.

 

[Henning]

Oh, BTW, if you really want to increase your echo across X & S band radars, these are the ticket, kinda pricy as safety gear though for aviation people.

http://www.defender.com/product.jsp?path=-1|135|2290117|2290118&id=2025506

You can mount it inside your empennage if it's glass, wood, or fabric.

 

[Henning]

Pretty hard for me to justify putting a $3,000 box in a $9,000 airplane.

Can you buy another plane with the box in it that does the same thing for $12k?

Have you called White Industries about a used txp? Have you considered hanging an alternator between the gear and powering it with an Ag pump drive fan/prop? There are also the kits for the old disc drive motors to turn them into wind generators.

I bet with a bit of thought, effort, and scrounging you could put in an electrical system and txp for <AMU.

 

[JimNtexas]

Oh, BTW, if you really want to increase your echo across X & S band radars, these are the ticket, kinda pricy as safety gear though for aviation people.

Reception frequency: X Band Radar 9.3 - 9.5 GHz , S Band Radar 2.9 - 3.1 GHz

That there are no ATC radars in the 9ghz band, and the 2.9-3.1 frequency is higher than most terminal area radars.

But that device will reduce the chance of boat-airplane collisions. I'm not sure if it would help or degrade attacks from an SA-2 Guideline.

 

[PW_Plack]

I'm trying to imagine something that would connect the coax to the center of the ears.

I did a demonstration during an antenna forum at a fly-in of what I call the "CLA Dipole," as in "crap lying around." I stuck a piece of 2"-wide aluminum-foil plenum tape to a scrap piece of 3/4" particle board, used a box cutter to slice a 1/4" gap in the middle, and used two self-tapping metal screws through the tape into the board to attach the coax. It had a VSWR of 1.1:1 and worked well after trimming for resonance at 120 MHz, and was under 1.5:1 over most of the band. Two years later I pulled it out of the garage and it still worked.

I would look for a liquid plastic or epoxy product which could be used to make a raised bump at the feedpoint, and mold it to surround a couple brass chassis standoffs or other small threaded fittings to accept screws if I was making a real one. And I'd also use a ferrite-bead current balun (and coax with a good shield).

I've also thought about capacitive coupling using a couple small squares of copper tape, to allow soldering the coax and to avoid dissimilar metal contact (which could be trouble later).

Experimental aircraft allow fun experiments long after the build is completed!

 

[weirdjim]

I did a demonstration during an antenna forum at a fly-in of what I call the "CLA Dipole," as in "crap lying around."

I would look for a liquid plastic or epoxy product which could be used to make a raised bump at the feedpoint, and mold it to surround a couple brass chassis standoffs or other small threaded fittings to accept screws if I was making a real one. And I'd also use a ferrite-bead current balun (and coax with a good shield).

I've also thought about capacitive coupling using a couple small squares of copper tape, to allow soldering the coax and to avoid dissimilar metal contact (which could be trouble later).

Experimental aircraft allow fun experiments long after the build is completed!

You would have fun at the RST Skunk Works out here in Grass Valley. We have more CLA projects laying around that the law should allow. I'd love to specify 2" (or even 1") copper tape for my plastic plane antennas, but 1/2" is the most commonly available width I can find without special order. Double-width 1/2" is OK, but unless you use the tape with the copper-loaded adhesive so that the strips are well bonded to one another you can get some "interesting" results.

As to dissimilar metal corrosion, as you noted, if you can exclude moisture from the junction, that problem goes away. Potting the joint when it is VERY dry is a great solution.

BTW, what happened to the fuel situation at Morgan County Airport? It used to be the only mogas stop between California and Denver. I see it all went away.

Jim