 |
 |
 |
|
|
The
easiest balun for 0.1 to 50 MHz. Mode of operation: The antenna tuners in standard transceivers or external coax-antenna tuners have only a limited impedance-range for matching. The matching of a shorter wire (according to the wavelength) with this big impedance is often not possible. Besides this, the wire is normally outdoor, and the antenna tuner is near the tranceiver, so it's sometimes difficult to connect up to the tuner. Remedy: an automatic antenna tuner of SGC, directly connected to the antenna, price about 1000 DM... However there is a cheaper alternative: The MTFT !! The MTFT is a impedance transformer with a transmission ratio of 1:10. The transformer steps down the extremely high SWR of the wire so that it's possible to connect up to a normal simple tuner. The balun should be fixed directly on the antenna and no coax cable is to be connected between the balun and antenna. From the balun, a coax cable is connected to the transceiver. The SWR on this cable is normally less than 3:1, so the loss will be low. The length of the antenna wire should be min. 6m (ca. 236 inch). Connection to ground is recommended, to be connected to the shield of the PL-connector, not to the housing! If no ground is available the transceiver should be connected to ground. It may be necessary - in addition - to use an RF choke or by creating a simple cable inductor: ie. before you connect the coax-feeder with the balun, create an air-coil with 5-10 turns of the coax with a diameter of ca. 30cm (ca. 12 inch´. Instead of a ground you could also use a wire radial or the other half of a dipole. F6JSZ has a windom mounted, with a length of 20m (ca. 8 inch). The feed is fixed at the 1/3rd in relation to the complete length over the MTFT (pull relief is necessary for the dipole!) and the coax-feed length is 20m also. F6JSZ wrote in the french "CQ" magazine that his SWR on all HAM-bands is less than 1.5:1 and he needs no tuner. You can use the balun for other purposes than just as wire antennas. eg. CB-antennas can be matched easily into HAM-bands. Different metal objects can be used as antennas with the balun e.g. guttering, lamp stands, or the chassis of a car (works on 40m)... Ideal for people who like to experiment !.. The max. output is 150 W PEP. It's also a good additional part for SWL's: With this balun the gain is higher for world-reception than when using a simple wire. Furthermore, an additional tuner is not required.
|
|||
