Hello Everyone! Tapos na ang Undas, tulog na ulet mga patay. Gisingin natin itong topic! A little bit more about tuned coils. We all played with magnets,right? In fact, it will be the first display in my SCIENCE FAIR for school children. MAGNETISM IS AWESOME! REALLY IT IS. ALL OF US GOT EXCITED AT THE INVISIBLE ENERGY IN A MAGNET. WOWOWEEEE! We also learned polarities. North, South we called it. North and North repels and so with South and South. But N and S attracts. First law! Well, look at batteries, you cannot connect the minus to the minus nor the plus to the plus. It's always plus to the minus to chain a series of batteries. So, with magnets, you can connect several into a link but it has to be N to S, N to S, etc.... MAGNETISM IS LOCKED ELECTRICITY! WOW! WHATDYAMEAN? Let us get a coil and connect the terminals to a tester or even an LED. Get a magnet and swing it in front of the coil. VOILA, the tester jumped or the LED lighted. This is my second demo in the Science Fair. The magnet INDUCED current into the coil. MAGNETISM BECAME ELECTRICITY! The current was not produced when the coil sensed the magnet. It was when the magnet was removed! The magnet produced a magnetic field around the coil and when the field collapsed, energy was absorbed by the coil. WAIT A MINUTE, WE ARE SUPPOSED TO DISCUSS COILS. EHEM...her we go.. The above was important cuz we will discussed magnetic fields. Ah, we go no further, let us talk about the AM antenna, which is a tuned coil! The antenna coil is like the coil discussed above. We do not need a magnet cuz electric fields abound in the atmosphere. All transmitters put electromagnetic waves. and while we had to swing the magnet, we do not have to swing these waves simply because they are ever changing poles. They are AC and AC can induce current to another coil! If the coil is by itself an electric generator, how do we collect the energy? Well, the capacitor is actually a battery with a very short storage life. We put a capacitor across the coil and might as well make the capacitor variable. When the coil discharges into the capacitor, the capacitor , being a battery, will in turn re energize the coil. The result is a SYMBIOTIC relationship. The pair will alternately charge each other. and not only that, changing the value of the capacitor will change the frequency of the exchange. A pair like this became known as a "tank". YOU MEAN THERE IS ALWAYS CURRENT THERE? Yes, and we call it signal because it is minute. If we connect a long wire antenna and ground the other end of the coil, we can obtain max energy and we DIRECTLY convert the signal to DC with a diode and hear the station! It is called direct conversion and uses no battery. They were called Foxhole radios during World War II. SO, THE FIRST TRANNY IS TO AMPLIFY THIS TINY SIGNAL! YEP...