Many enthusiasts like to make their own antennas, and I am one of them. On the other hand, there are not many commercially available aerial band antennas, and in order to improve the listening effect, homemade antennas are also a last resort.
Half-wave dipole antenna, as the name suggests, is composed of two symmetrical oscillators, each with a length of 1/4 wavelength and a total length of half a wavelength. The two oscillators can feed through a 1:1 balun, convert the balanced signal into an unbalanced signal, and then transmit the signal to the receiver via coaxial cable, which is simple and practical, and it is easy to make your own.
1. Make an antenna oscillator
The aviation band frequency is 118-136Mhz, and the center frequency is 127Mhz. Since it is only used for signal reception, there is no need to consider factors such as transmission efficiency and SWR, so the oscillator length can be roughly calculated. Using the formula wavelength (m) = wave velocity (km / s) / frequency (MHz) for calculation, the shortening coefficient is taken by 5%, the calculation result is: 299.79 / 127 * 0.95 / 4 = 0.56, so intercept two 0.56 m long diameter 4 mm multi-strand semi-hard copper wire as oscillators.
2. Make a 1:1 barron
A balun is a device that connects a balanced transmission line (with two conductors, opposite directions, a line with equal currents, for example, a twisted pair cable) to an unbalanced transmission line (a line with only one conductor and ground, e.g., a coaxial cable) that converts the unbalanced signal into a balanced signal and vice versa.
When winding, three 1mm diameter enameled wires are used on the inner diameter 18mm ferrite magnetic ring and 10 turns, the balance end outlet is connected to the antenna oscillator, and the unbalanced end outlet is connected to the M head base, as shown in the following figure:
3. Antenna assembly
The wire lugs are welded at one end of the oscillator and then the two input terminals of the balun are connected. One end of the coaxial cable is connected to the baron through the M male, and the other end is selected according to the receiver's antenna interface type, and the common ones are M-head, BNC and SMA.
4. Antenna erection
The antenna can be set up horizontally (that is, two oscillators are fixed horizontally, the same below), vertically, positive V or inverted V, and the listening effect can be easily compared by changing different erection methods.
(The author found that the vertical erection effect was the best through comparison, and received a broadcast from the airport 70 kilometers away!) ）