RADIOAMATORI-Long Wire la prima antenna radio #radioamatori#antenna #scienze#technology#hamradio

Hi everyone, if you're new to shortwave, or rather, HF, you need a simple, reliable antenna. In just a few minutes, you can build a "Long Wire" of any length, with wire lengths ranging from 10 to 50 meters, matched to the transmission line using a 9:1 ratio Un-Un or Bal-Un toroidal transformer. LONG WIRE In principle, wire antennas are built for obvious space reasons, typically with lengths of 1/2 lambda or multiples thereof, maintaining the firm assumption that the closer these values ​​are respected, the better the performance. For the Long Wire, the situation is slightly different. Since this is a broadband antenna, to ensure satisfactory performance across the entire HF range and beyond, you must avoid cutting the radiating cable at a length of half a wavelength or multiples thereof. This principle applies to all frequencies you intend to operate on. The LONG WIRE also features a horizontal radiation pattern with 45° main lobes (which tend to narrow as the frequency increases), plus various other secondary lobes, WHICH determine a slight directionality. A radiating electric wire, used as an antenna, with a length between 10 and 50 meters, can have a typical impedance of approximately 400-600 Ohm. The insertion of a magnetic BAL-UN transformer with a TRANSFORMATION ratio of 9:1 allows us to easily bring the system to a typical value of 50 Ohm on all the bands of our interest and therefore be able to adapt it to all Amateur Radio transceivers on the market with an SWR/SWR ratio close to 1:1/1:5. It goes without saying that the use of a tuner is advisable to adjust for any mismatches at the band extremes. The length of the radiating wire can depend on many factors, one of which is the available space. I bring you this snapshot with the most common measurements used for this antenna. As you can see, along the HF frequency spectrum and within an approximate measurement of 30/40 meters, there are some measurements that offer a very low SWR... 16.20 meters or 30 meters are standard measurements for optimal operation. For the balun, a TOROID is needed, where 9 to 15 THREE-WIRE turns of enameled copper wire are wound and crossed as shown in the drawing. Everything must be wired inside a waterproof box, from which only the SO239 connector for the drop cable and the bushing for the ANTENNA wire will come out. To power a Long Wire, you need to use a particular type of Un-Un Magnetic Balun with a 9:1 transformation ratio. To start building it, you need to get an Amidon FT240-43 toroid; Some advise against using the T200-2 or T200-6 because they are high-Q toroids suitable for narrow-band resonant antennas. In our case, however, working with a wide-band antenna, a low-Q toroid would be more suitable, thus allowing for a broader frequency spectrum. Toroids are divided by MIXTURE, COLOR, AND FREQUENCY. The ones that interest us amateur radio operators are very easy to find: RED = 1-30 MHz YELLOW = 2-50 MHz BLUE = 0.5-50 MHz