- #UNDERSTANDING BUILDING AND USING BALUNS AND UNUNS DOWNLOAD SKIN#
- #UNDERSTANDING BUILDING AND USING BALUNS AND UNUNS DOWNLOAD FREE#
Antenna impedances are highly dependent on proximity of the earth, and other objects such as trees and buildings.
#UNDERSTANDING BUILDING AND USING BALUNS AND UNUNS DOWNLOAD FREE#
6ħ Why Impedance Transformation? REASON #2 for BALUNS Antennas aren t usually 50 or 72 ohms, even though theory (properly) states a dipole is 72 ohms (only in free space, far from earth). Now have current on OUTSIDE of coax undesired! Feedline now radiates and is part of antenna changes the radiation pattern, may place RF in the shack when touching ground.
#UNDERSTANDING BUILDING AND USING BALUNS AND UNUNS DOWNLOAD SKIN#
1 Baluns, Ununs, and Related Topics W7KVI, HARC Original: 3/26/16Ģ This Presentation Informal & brisk - 52 slides (too many unless you re an enthusiast!) Discussion encouraged if not extensive, interrupt me freely My motivation commercial, popular balun kit, inexpensive, insufficient instructions installed on a 75m dipole, poor resulrs 2ģ Major Topics Why Baluns? Applications Types of Baluns Examples 3Ĥ Why & Where? Why do we need baluns and ununs? Prevent current on outside of coaxial cable shield, which causes radiation pattern distortion Due to Skin Effect Convert impedances Reduce need for, or demand on, antenna tuner Prevent transmitter foldback at ~2:1 SWR Typical applications Connect balanced and unbalanced structures Dipole to coax Balanced feedline to coax Use antenna on non-resonant frequencies 4ĥ Property of AC current to flow mostly near the surface of a conductor Skin Depth thickness containing 63% of current Skin Effect Inside of shield conductor 1 for GROUND of coax Outside of shield conductor 2 for GROUND of coax At 10 MHz, skin depth = 21 µm, or m Coax shield thick enough that it actually represents 2 separate conductors inside and outside of shield Cross-Section of Coax Allows using pipes or tubes to reduce conductor cost 5Ħ Unbalanced Coax connected to Balanced Antenna REASON #1 for BALUNS Current from coax shield to dipole conductor (or reverse) has available 2 paths inside and outside of coax shield.