| Balun 1:1 do W3DZZ |
| @Andrzej, SP8LBK. W innym wątku tego forum (Co można na szybko zrobić z LEMM AT-92 ?) polecasz taki oto dokument (fragment "The ARRL Handbook"): http://ot20.pzk.org.pl/infusions/pro_download_panel/download.php?did=160 w którym to na stronie 20.8 można przeczytać następujący akapit (zamieszczam w całości żebyś nie musiał szukać): Baluns A balun is a device for feeding a balanced load with an unbalanced line, or vice versa (see the Transmission Lines chapter of this book). Because dipoles are balanced (electrically symmetrical about their feed-points), a balun should be used at the feed-point when a dipole is fed with coax. When coax feeds a dipole directly (as in Fig 20.7), current flows on the outside of the cable shield. The shield can conduct RF onto the transmitter chassis and induce RF onto metal objects near the system. Shield currents can impair the function of instruments connected to the line (such as SWR meters and SWR-protection circuits in the transmit- ter). The shield current also produces some feed-line radiation, which changes the antenna radiation pattern, and allows objects near the cable to affect the antenna-system performance. The consequences may be negligible: A slight skewing of the an- tenna pattern usually goes unnoticed. Or, they may be significant: False SWR readings may cause the transmitter to shut down or destroy the output transistors; radiating coax near a TV feed line may cause strong local interference. Therefore, it is better to eliminate feed-line radia- tion whenever possible, and a balun should be used at any transition between balanced and unbalanced systems. (The Transmission Lines chapter thoroughly describes baluns and their construction.) Even so, balanced or unbalanced systems without a balun often operate with no apparent problems. For temporary or emergency stations, do not let the lack of a balun deter you from operating. Pozdrawiam, |