Question by Naniel: Why do some antennas only have one connection to the radio, while others have two?
From what I understand, radios receive a signal because an electromagnetic field is moving around a wire (the antenna). This creates a very small electric current which is then amplified into an audible signal. I would think that the antenna would have to have two connections to the radio in order to complete a circuit for electricity to move through. Yet some radios only have a telescoping antenna that has a single wire going to the circuit board. How and why does that work?
Answer by Violet W
You are correct that there need to be two paths, one in, one out for the electrons. Antennas with two wires typically are balanced antennas, such as a dipole antenna. Electrons move along one arm toward the receiver, through the receiver, and out along the the other arm. Then they reverse.
With a single connection, such as from a vertical antenna (a single conducting mast sticking up vertically), when electrons flow in to the receiver, they have to go somewhere. If the receiver is connected to earth via a wire, usually the receiver is set up so that those electrons flow into the earth. And on the other half of each cycle, the electrons flow out of the earth, through the receiver, and into the vertical antenna.
But what if there is no grounding connection to the earth? Radios work because they couple capacitively to the earth. It is a very weak connection, but sufficient for minute signals. The radio’s internal ground plane, to which the other end of the tuning coil is connected, acts as one plate of a parallel-plate capacitor. The earth forms the other plate. So electrons flowing into the coil flow onto the ground plane. That creates an electric field that interacts with the electrons in the earth, just as they do an any capacitor.
Often a one-wire antenna radio will receive better if a physical wired connection is made from the radio’s tuning coil (or ground plane) directly to the earth, or to a large piece of metal that couples to the earth (capacitively) even better than the radio does.
Back to the vertical antenna, it turns out that the earth is a ground plane that acts as a mirror for radio signals emitted by or received by a vertical antenna. Being a mirror, the earth acts virtually the same as if the vertical antenna had been a true dipole with two arms. The earth takes the place of the second arm. The ground plane of the earth typically is effectively at a depth of about 6 feet (2 meters), but it varies with soil conditions.
Electrons are conserved in the receiving process.
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