In the American Journal of QST for 1973 hobbyist WA1MKR Max Blumer was proposed antenna, which is a wire loop with a perimeter equal to the wavelength. The figure shows that the wire loop and the principle of its formation. Was based on a common loop antenna ( left panel ) , power points X and Y. This wire frame radiates vertically polarized wave in two directions perpendicular to the plane of the frame antenna A-A '. The figure shows that the center of the antenna is converted into a rectangular wire antenna , wherein the antenna radiation characteristics are not changed. In the following figure the rectangle becomes a cube . With this transformation of the perimeter wire antenna remains unchanged, but the most important thing that the length of the sides of the new antenna is transformed into a cube is reduced to a length of L/10. But unlike conventional wire- frame in this changing pattern of the antenna in the vertical plane of the antenna also radiates vertically polarized wave , but the direction of the radiation is not bi-directional and omni-directional . Author WA1MKR this antenna realized this dish with origins in the 144 MHz antenna is connected to the coaxial cable with an impedance of 50 ohms. SWR was 1.2 ... 1.4 . In the study of pattern was found that all the same it is not really a pie chart , probably because of the shielding properties of the cable and the structure. In the future, the author WA1MKR was made the same wire antenna but for the range of 21 MHz in this band , it was almost the same features except for the SWR, it is not much higher. The antenna has shown good results.
Saturday, October 12, 2013
Not always, amateur radio is the ability to set effective long wire antenna for the 3.5 and 7 MHz . If you want to install a wire antenna type inverted V and there is no place you can upgrade this antenna a bit , reduce the size of the antenna input of the extension coil . As can be seen from the figure below size wire antenna extending spools approximately equal to the size of half-wave dipole for 7 MHz . The mast antenna has a small height, which is approximately 7 meters, the lower ends of the antenna is at a height of approximately 1.5 meters from the ground . Also from the figure that the power antenna wire modernized type inverted V through the delta transformer via a coaxial cable with an impedance of 50 ohms ... 75 . For a more exact matching transceiver must have the tuner . Since this wire antenna significantly affects the properties of the soil ( container terminal ) , then after the installation requires careful tuning . When you set up a wire antenna to watch its resonance and SWR. Changing the resonance of 100 kHz to 3.5 MHz band can occur when the length of the segment b by 5 centimeters. If you still do not get the minimum SWR you can try to change the point of connection of the delta - the transformer. With this upgrade wire antenna type inverted V, the antenna in the range of 3.5 MHz to baseband . This antenna is useful in field conditions and in areas with limited space.
Posted by karan at 12:51 AM
Sunday, October 6, 2013
It is known that the directivity pattern of a conventional dipole antenna has the shape of a horizontal eight . It is obvious that in order to be able to carry out qso with correspondents located in different areas of need for this dipole is placed on the rotator . But if you do not have a rotary device that can apply an antenna system of two perpendicular arrangement of the two dipoles. This dipole antenna system is connected via a single coaxial cable dipole excited with a phase shift of 90 degrees to form a cross-shaped antenna ( first figure) . Diagram of a cruciform dipole system in the horizontal plane has a substantially circular shape . From this figure it can be seen that both dipoles are connected through the quarter wave transformer . Strengthening of the cross- dipole system is not great and there are some difficulties in the negotiation. Increase efficiency of the antenna system and hence its gain and to avoid difficulties in coordination can be applied if the antenna system is based on loop dipoles such loop dipole itself has a higher gain and efficiency than conventional bit wideband linear dipole. In the second picture a) - wiring diagram of the dipoles and Figure b) - the radiation pattern . As can be seen from the figure the coaxial cable is connected directly without the agreement and the point where the cable impedance of 75 ohms . Input impedance of each dipole is 300 ohms. Dipole disposed at a distance equal to L / 2 (half wave ) . Currents flowing in the opposing antennas are shifted from each other by 180 degrees, and thereby forming a circular pattern . Placing a few of these antennas on top of each other giving you greater gain relative to a conventional dipole.
Posted by karan at 7:26 AM