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Simple 50MHz-J-Pole-Antenna The principle of the Wireman-J-Pole: The picture shows the currents in the antenna. At the both ends of the Lambda/2-section you have a high impedance (some KOhms) and a low current. At the other side at the end of the Lambda/4-line is a maximum of the current (low impedance of about 20Ohms). The two ends are connected together through the metal of the coax-socket (see next picture below). At the points XX you can find a 50-Ohm-point for feeding with the coax-cable. Because the quarterwave-line is symmetrical, you should feed with a lambda/4-choke for a SWR of 1,0 at 50,150MHz. The bandwidth for a SWR <1,5 is greater than 1 MHz. The gain and pattern are the same as with a normal vertical dipole, but feeding is much more easier. For the elevation plot and gain look at the other vertical with a Collins-filter! |
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