Transmission Line Considerations WZ4O

Types of Common Transmission Lines

Impedance of Transmission Lines

Impedance of Transmission Lines

Impedance of Transmission Lines Properly balanced line will not radiate

Note: Larger coax diameters generally have less loss Loss goes up with frequency Question: At Field Day, we have two 100 foot sections of coax that we need to connect together to get to our antenna, both with 2 dB/100 feet of loss on 10 meters. What will be our total loss? Question: We need a 50 foot length of coax to get to our antenna. The loss is rated at 4 dB/100 feet at 70 cm. What is the loss in 50 feet of this line?

Sources of Loss in Transmission Lines (Current) Current in transmission line @ 100 watts: P = I*E = I*I*R > P = SQRT(P/R) 50 ohms: I = 1.414 amps 300 ohms: I = 0.577 amps 600 ohms: I = 0.408 amps

Sources of Loss in Transmission Lines (Dielectric)

Sources of Loss in Transmission Lines (VSWR)

Sources of Loss in Transmission Lines (VSWR)

Parallel Wire Balanced Line

Notes: Don’t bend coax too sharply Seal all outdoor connections…braided shield acts like a wick to moisture Coax CAN be taped to tower legs Coax runs CAN be taped together Window line can change characteristics in rain Keep balanced line balanced – NEVER run next to metallic objects Do NOT tape to tower legs – use standoffs