Hobbies And Interests
Things You'll Need
Instructions
Wrap the copper wire tightly around a section of cardboard packing tube. You have many choices. As an example, assume you have a 10-cm diameter tube wound 80 times making a coil length of 1 cm.
Calculate the inductance of your coil. The inductance is given by:
Calculate the capacitance needed to make your coil sensitive to radiation at the frequency of interest. The capacitance is given by
Ground one end of the wire from your loop antenna and connect it to one lead of the capacitor, and connect that to one input of the amplifier circuit.
Connect the other end of the wire from your loop antenna to a resistor, connect the other lead of the resistor to the unconnected lead of the capacitor and connect that to the other input of the amplifier circuit. This resistor is designed to spread out the frequency response of your antenna. Because you don̵7;t need much spreading, you can use a low value, say 100 ohms.
Measure the output of your detector, which will be proportional to the electromagnetic fields in the region around the antenna frequency.
Inductance = (mu0 x r^2 x N^2 x pi / l) x (1 - 8 x r / (3 x pi x l), where mu0 is a constant equal to 4 x pi x 10^-7, r is the radius of the tube, l is the length of the coil, and N is the number of turns.
For the example, the inductance will be:
Inductance = (4 x pi x 10^-7 x 0.05^2 x 80^2 x pi/0.01) x (1 - 8 x 0.05 / (3 x pi x 0.01))
Inductance = 5 x 10^3 = 5 millihenry = 5 mh.
C = 1 / (Inductance x frequency^2).
For the example a detector sensitive to frequencies around 50 Hz would be given by,
C = 1 / (5 x 10^-3 x 50^2) = 0.08 farads, which is more commonly represented as 80,000 microfarads.