Please note: NVIS Propagation is only useful at frequencies below 10 MHz. They are good at turning you into "The Squirrel in the Substation". Dimensions will change slightly due to antenna height and ground conductivity variations.and Keep The Antenna Away From Power Lines. Please note: The calculations are approximate, so some final end wire length adjustment may be necessary. Several antenna / reflector elevation options are shown that enhance the NVIS vertical antenna pattern and propagation. Hardware cloth or "Poultry Screening" is an option too. The Ground Reflector can be a single conductor or several in parallel spaced a few feet apart. The antenna as fed matches reasonably well into a 50 Ohm Coax Cable Feedline and an antenna tuner.Ī Ground Reflector can be added to enhance NVIS Propagation at frequencies below 10 MHz where NVIS Propagation is usable. This helps to provide acceptable matches on frequencies other than what the antenna was specifically designed for. The braided copper shield of the coax is the actual RF radiator, and the center conductor acts like a balun or matching transformer to provide a DC ground. It is made of coax cable, instead of a single strand of copper wire. The antenna as designed is a broad band antenna with the coaxial cable's capacitive reactance changing to compensate for changes in inductive reactance across the band of operation. It’s Called A Double Bazooka The Double Bazooka is a unique design alternative to a dipole. Each end of the coaxial span has the braid and center conductor shorted and connected to the end wires. The center conductor and dielectric is not disturbed and the two separated braids are then fed with the Coax Feedline. The span is opened in the middle to expose the braid from each half. The antenna is constructed from a single length of 50 or 75 Ohm coax with a coaxial feed point in the center. 300 Ohm Twin Lead with the ends shorted is an option for even greater bandwidth. The larger the wire, the wider the bandwidth. The End Wire Size can range from 16 AWG to 12 AWG.
The measurements below are for building a Double Bazooka Near Vertical Incident Skywave (NVIS) Antenna.
0 kommentar(er)
