Mapleham Study — Chapter 6

Chapter 6 — Key Takeaways

Transmission Line Types — coax 50 ohms unbalanced or ladder line 300 to 600 ohms balanced, impedance determined by geometry and dielectric
Balun — converts balanced to unbalanced, needed when connecting dipole to coax
Connectors — PL-259 for HF, N-type for VHF and UHF, BNC for test equipment, SMA for handhelds
Line Loss — increases with length and frequency, RG-58 has excessive loss at 70 cm, use RG-213 or LMR-400 for UHF
SWR — 1 to 1 is perfect match, below 1.5 to 1 acceptable, high SWR causes reflected power back to final amplifier
Antenna Tuner — transforms impedance to 50 ohms, does not make antenna resonant, protects solid-state finals
Dipole Formula — 150 divided by frequency in megahertz gives total length in metres, feed point approximately 73 ohms in free space
Polarization — electric field orientation, VHF and UHF FM uses vertical, HF DX uses horizontal for lower ground loss
Wavelength Formulas — 300 divided by frequency gives wavelength, quarter-wave is 75 divided by frequency, half-wave is 150 divided by frequency
Yagi — driven element, reflector longer, directors shorter, parasitic elements energized by electromagnetic field
Vertical Antenna — quarter-wave plus ground plane, requires radials, loading coil for mobile operation on lower bands
Loop Antennas — quad uses full-wave loop per element, delta loop is triangular, polarization depends on feed point