This antenna can be used in cases when there is not enough space to install a full-sized dipole on 160m. It should be noted that, calculated using the relationships given in this article is equivalent to a shorter antenna can be made on other Amateur bands.
The antenna consists of (see figure) emitter length And lengthening the coil L1. This coil "lengthens" the transducer to the electrical length L/4, and as the ground using a pole and grounded In the reinforcement of the building. To improve the efficiency of the antenna, if possible, it would be good to set a shorter counterweight D with a lengthening coil L2. Better if balances will be few.
The calculation of the antenna is produced in such sequence. Defining the length of the emitter And (m), choose the resonant frequency of the antenna f (megahertz) and the diameter d (meters) wire, which will be made of the emitter. The following example of the calculation used the following values of these parameters: A=29 m, f=1,86 MHz, d=0,0015 m(1.5 mm).
First, determine the wave length L (meters) for a selected resonant frequency of the antenna, its working angle f (degrees) and the intermediate parameter S:
For our example, L=161.3 m, f=64,7" and S=19333. Then find the characteristic impedance Z (ohms) of the antenna conductor and the corresponding reactance of the antenna XC at the connection point of the inductor L1 to the canvas of the radiator:
For our example, Z=600,6 Ω and XC=And 283.8 Ohms. Note that the reactance shortened emitter capacitance. Therefore, to tune the antenna to resonance is used, the inductor L1. Its reactance (XL) should be numerically equal to the reactive impedance of the antenna CH. Coil inductance L (microhenry) is calculated by the formula
For our example, L=24,3 µh. Braid power cable connected to the left (in the drawing) end of the coil L1 and the center conductor to the outlet from the coil. Connection point (n1 turns, counting from the left end of the coil depends on the wave resistance of the supply cable R, the inductive reactance of the extension coil and number of turns n. They are connected by the relation:
If, for example, lengthening the coil L1 has 28 turns, and the wave resistance of the cable is 50 Ohms, then its center conductor should be connected approximately to the 12th round. More precisely, the connection point is determined experimentally by minimum SWR in the supply feeder.
Lengthening the coil is calculated according to standard formulas. Because when you work on it there is a high RF voltage, the coil is better to make a single layer with a forced step of winding equal to the diameter of the wire used for its production. This wire should have a diameter not less than 1 mm.
In the original article (K. Bottcher. Endgespeiste 160-m-Antenne fur ungun-stige Lagen. - Funkamateur, 1997, N11, s. 1314-1315) noted that lengthening the coil can be performed on an annular magnetic core of carbonyl iron, if the transmitter has a small capacity, and the diameter of the magnetic core will be a few centimeters.
Publication: N. Bolshakov, rf.atnn.ru