The problem of antennas with reduced size remains important, especially for radio Amateurs living in large cities.
As a result of experiments with various types of shortened antennas design, which is a good compromise between the smallest possible size and efficiency of the antenna.
Antenna (Fig. 1) is of absolute simplicity in fabrication and setup, takes up very little space (the height of the dipole over 1.5 m), can be installed on the balcony, to gain a foothold on the wall, etc.
The antenna can be used, besides the usual bonds, and the alarm system to communicate with the house, etc.
The author's antenna is located on the 4th floor inside panel 9-storey building and is essentially a room. Structurally, it is suspended at its upper point through the insulator to the eaves above the window.
The antenna is a vertical dipole with capacitive loads at the ends. The shoulders of the dipole and a capacitive load is made of copper wire or rod with a diameter of 2.5... 5.0 mm. the Connection arms of the dipole and capacitive loads is made by soldering.
The connection between the coils L1 and L2 are inductive. Structurally, the coil L2 is in the middle of the coil L1. The turns of the coil L2 is located between the turns of L1. L1 and L2 are wound on a ceramic frame with a diameter of 8 mm. L1 contains 15 turns of wire PEL-0,8. The winding step of the coil L1 - 1 mm and L2 contains 3 coils wire PEL-0,8. As C1 is applied KPE capacity 12...150pf.
As a matching device between the feeder and the proposed antenna can also be configured to apply a symmetrical circuit described in [4], by choosing the optimal starting feeder in the contour data and leaving the coil L1 and the capacitor C1 is unchanged.
Coaxial cable may have an impedance of 50 or 75 Ohms.
Since the dipole is vertical, it is desirable to cut the cable perpendicular to the emitter, was as long as possible. The antenna tuned to the desired frequency by capacitor C1 to the maximum of the indicator of the field strength or the minimum readings on the SWR meter. The dimensions of the shoulders 11 and 12 of the dipole was chosen so that the entire antenna fits within the window opening. If the radio has the ability to increase the length of the shoulders 11 and 12, the efficiency of the antenna can be increased.
When you work with an antenna you need to remember that like any shortened antenna, it is susceptible to the influence of close objects, wires, etc., and also quite narrowband.
The results of antenna testing with portable and car radio are represented in table. 1.
Range confident communication in terms of Kharkov 1. Portable a/C "informtekhnika" receiver Sensitivity 1 mV. P o=0.5 W 5 - 6 km 2. A/C -COBRA 19 PLUS receiver Sensitivity of 0.5 µv, pout=4W 15 - 20 kmLiterature
Author: S. Zaugolny (LA-00299); Publication: www.cxem.net