180Antenna System Hints
- 4. Nov. 2013Hello LowBandDXers!
Good infos from Ameritron.
ANTENNA SYSTEM HINTS
1. Many people believe a ladder line fed antenna requires a 4:1 balun. The input impedance of a ladder line feedline can actually range from a few ohms to many thousands of ohms, depending on feedline and antenna length. The best balun for such systems is always a 1:1 current type balun. A current or choke-type balun guarantees minimum feedline radiation and maximum balun efficiency and power handling.
2. As a general rule, all balanced antennas should employ a choke-type balun at the feedpoint when fed
with unbalanced (coaxial) feedlines. It is often a good idea to use a choke balun near any coax fed antenna regardless of antenna type. Considerable common mode currents can flow on the outside of coaxial cables, even when feeding groundplane or gamma matched antennas, since systems are seldom perfectly designed or constructed.
3. Avoid feeding unbalanced antennas (like verticals) with balanced feedlines. Even if a good balun is used at the tuner, the line will still radiate.
4. Good antenna and feedline balance will often reduce RFI to your neighbors, as well as reduce noise coupled into your receiver from the feedline.
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