Mylar/aluminum foil helium filled balloons - Do they affect radar?
470729
a good radar reflective surface has to be hard and flat, just like a ball bouncing back off a wall, you want the radar reflection to bounce back to the receiver with most of the strength that was sent out so you can get a good 'reflection'\nthe balloon is round so not a good reflective target, the aluminium is a metal so a good reflective material, it all depends on the line of sight as well. If the balloon was right in the middle of the radar beam width it might give of a weak sig? depends on the size of the balloon as well. A huge blimp of that material would give a better reflection than a normal size balloon. Hope this was a help.
467769
This is an important question - the health effects of microwaves.  Some comments: Lead is not necessary.  Lead stops ionizing radiation like x-rays, but for reflecting microwaves, any conductive metal will do; aluminum is the most commonly used for microwaves, and is a better conductor than lead.\n   Metal mesh will work, just like in a microwave oven, but the problem is, it will only be really effective if you build a sealed box.  If you only cover the windows, the microwaves will come through the walls, floors and ceiling.  Also, at the joints between sheets of metal mesh, you need to have a continuous eletrical connection.  Any seam which is unconnected over a few inches will allow power in.  A large seam may behave just as if the mesh is not there at all.  (This is why a cell phone will sometimes work in an elevator, and sometimes not)  \n    I would think that using aluminum adhesive tape running down the seams of the mesh on both sides would work. \n    Anything that only covers one wall or less may help, but it may not help at all, as microwaves bend around the edges of shields, and also are reflecting off all the other parts of your building.  Any non-sealed metal mesh structure will interact with the radiation field as a open metal resonator in a very complicated way, which is hard to predict and depends on the specifics of the metal geometry, the direction and frequency of the radiation, and all the collection of reflectors in your building (pipes, wiring, window screens, reinforcing bars in concrete).  However, if the metal mesh box is truly sealed and has no open seams whatsoever, you are 100% safe.  People build these out of mesh for low-noise testing chambers, but they are hard to build, especially around doors and inlets for electrical wires and plumbing.  It really is a huge undertaking for a non-professional, sorry.\n     One final comment: you can take some comfort in the fact that if what you see outside your window are dishes, they are highly directional antennas.  Typically, they direct nearly all of their power in a cone within 1 to 4 degrees angle of the satellite or receiver where they are aimed.  Typically, stray radiation (called sidelobes) are 30 dB lower, meaning that the power radiated in other directions is one thousand times lower.  \n      Cell phone towers, however, which do not look like dishes, but an array of typically three or more panels, are not directional, and spray alot of microwave power in all directions.\n     Is there a health risk?  I'm director of a microwave engineering firm, and I don't know the answer for sure.  Just not enough data.  In my own laboratory, however, I always take all precautions to make sure no one is ever exposed to any microwave radiation, just in case.  There are national standards which govern the equipment outside your window, which do specify a maximum 'collateral' radiation level, which is deemed to be safe, based on what data does exist.  I would tend to believe that it is extremely likely they are correct about these levels being safe (safe meaning less likely to hurt you than the air pollution you breathe, the chemicals in the products you use, etc.), but we cannot be 100% sure.\n    Personally, I would be fine with living in an apartment looking out on a bunch of dish antennas, but if it was directly adjacent to a cell phone tower or building with cell phone array on it, I would not want to expose my family to it, and would move out.
482962
Radar works because radio waves are reflected off of many objects. Stealth fighters are designed to hide from radar by minimizing the amount of radio waves reflected. I am sure a technologically advanced civilization could hide from our radar, however that would also imply that they want to. If they were trying to make contact, I am sure they could make sure we see them on radar.
1105659
D'un point de vue mathématique, calculer la vitesse de la balle revient à résoudre un système de n équations différentielles avec conditions initiales. C'est un peu laborieux, donc dans la pratique on utilise effectivement un radar à effet Doppler, le plus souvent sous forme de canon.\n\n Ce radar est pourvu d'un émetteur à radio-fréquences (dans la gamme des micro-ondes) dont les ondes sont réfléchies par la balle en déplacement. Le délai de retour de l'onde est proportionnel à la vitesse de la balle. Ce délai est amplifié, filtré et analysé par une puce DSP qui pratique une correction d'erreurs et envoie les données analogiques à l'afficheur. \n\nA noter que les joueurs amateurs peuvent eux aussi chronométrer leur coup droit, grâce à un module de type Speed Trac qui s'accroche sur le filet. Ludique et pas trop cher.
21635
Meteorologists now use doppler radar to better define weather systems, especially rain clouds.  Theoretically this should permit more accurate seeding of clouds with silver iodide (from planes or the ground) to produce rain needed for crops.  At one time hurricanes were seeded with some success; but think of the lawsuits if they steered one your way and you lost your house!!!
809952
if your balloon were super super to the highest level so so so so so so so so so so so so so so so very very very very very strong.... as in... that it would survive at like zero pressure, your helium filled balloon would reach the outer space...\notherwise, it would'nt even reach the middle of the atmosphere..
211329
ABOVE IS A TRAITOR,SCUM (TO YAHOO!)\n\nIF I LIVED IN  PEORIA ILLINOIS, UNITED STATES OF AMERICA NA , MY TRUE LOYALTIES WOULD LEAD ONE TO THE TRUE DOPPLER RADAR PLACE AND THAT IS  >>>>>>> Y A H O O  ! <<<<<<< WEATHER.  ALAS YAHOO! WEATHER, CAN ANSWER THIS QUESTION.\n\nWHY SEARCH FURTHER WHEN THE ANSWER IS UNDERNEATH YOUR NOSE!  \n\nOF COURSE YOU CAN GO TO THE FAA .GOV  AND THOSE OTHER UNNECESSARY SITES ---- GO TO YOUR AIRPORT SITE  AND SEE.\n\nHAVE FUN AND A GOOD DAY!\n\nYAHOO! IS ALL YOU NEED !\n\n\nAPS
816061
It is tough to answer this question without knowing what the experimental procedure was or what the aluminum foil was used for.  More detail please.
932508
Microwave antenna's with ice shields.
1050743
A radar that is based in space!
161029
A dual radio frequency interferometer aided by laser rangefinder and terrain database system utilizes two linear rays of RFI sensors to determine the position of a source of RF energy. The dual RFI system is very attractive in that it is a passive system and cannot be detected by other sensors or systems while it is going through its position determination operation. Furthermore, use of two linear arrays of sensors allows for the elimination of chronic effects inherent in radio frequency interferometers. The two linear arrays can be placed anywhere on a vehicle as long as they are in the same common geometric plane and in-flight mechanisms are provided to transform the coordinate systems from the in-flight platform coordinates to the local geodetic coordinates. This provides positioning and source identification which can be beneficial to not only the present system but other systems in the area. With the two linear arrays, a line-of-sight vector can be determined and other systems can be provided with this information in order to provide further details of the source position. Once a pointing vector has been determined, this information can be used with other active systems in order to provide a precise range and location of the source of the RF signals.
28138
Infrared. Radar. Sonar. does that help?
634155
You can do what they do for airliners to protect them for radio interference.  Since an EMP is just a very concentrated radio wave this should work.  Take some tin mesh and wrap it around the electronic device you wish to protect.  This will create a great barrier because it causes the radio wave to be absorbed by it, with no damage to the electronics inside it.
602615
You shouldn't have many problems as they are a fair distance away. In the area surrounding overhead lines (and also radio towers, in particular mast antennas) it is dangerous to risk interference; e.g. flying kites or chain balloons, using ladders or operating machinery. However, you would have to be a lot closer than you are in order for there to be a problem. While there are claims that it causes problems, they are simply claims.
154920
I think you're referring to the radar gun that is used to measure the speed of a pitcher's ball. Yes, they work.
976120
Helium molecules are very small and slowly leak through the balloon wall.\n\nAir contains a mixture of gaseous molecules, primarily Nitrogen and Oxygen.  These are much larger than Helium.
796578
Yes, they do....sonar, for example.\n\nThe interface travel between water/air scatters the waves.  You'd probably have to keep the antenna under water.