The 1/2 Wave Dipole Length of dipole in feet = 468 468 f (MHz)
The 1/2 Wave Dipole Radiation pattern for a dipole antenna looking down from above the antenna
The 1/4 Wave Vertical Length of vertical in feet = Length of vertical in feet = 234 234 f (MHz)
The 1/4 Wave Vertical A side view of the radiation pattern of a 1/4 wave vertical. From above the pattern is round like a doughnut. A perfect ground would be a car roof.
The Yagi The yagi is perhaps the hams favorite directional antenna. They usually consist of one driven element, and several parasitic (un-driven) elements. Reflector (longer than driver) Driven Element (1/2 wave dipole) One or more Directors (shorter than the driven element)
The Yagi A 3 element HF Yagi A 3 element HF Yagi A VHF Yagi A VHF Yagi
The Yagi Gain Boom Feedline Reflector Director Driver The reflector acts like a mirror The director acts like a lens
The Yagi The yagi antenna focuses RF energy in one direction, giving the appearance of getting free power. This free power is called Antenna Gain.
Antenna Safety Dont put antennas. where they could fall across power lines Dont climb towers without a safety belt. Dont do tower work without a ground crew. If youre working under the tower, wear a hard hat.
Lightning Ground antennas when not in use. Ground the tower structure itself. Ground rods should be copper or copper clad steel and 8 ft. long. Disconnect AC power mains during storms, or use line conditioners or surge suppressors. GET OFF THE AIR DURING SEVERE STORMS!!
SWR – Protect Your Rig SWR (standing wave ratio) is a mathematical expression of the power going to an antenna and the power being reflected back. The idea is to get as close to 1:1 as possible. Most hams are happy with SWR of 1.5:1. The best way to get a good SWR is to cut the antenna to resonance.
Feed lines Feed line connects your radio to the antenna. Feed lines are either balanced (neither side grounded) like ladder-line or unbalanced (one side grounded) like coaxial cable. Either type can be used in your station. Coax is more popular and easier to work with.
Coaxvs.Ladder Line Can be buried or run near metal objects. Less RFI since outer shield is usually grounded. Weatherproof Easy to handle and connect Very low signal loss Can tolerate high SWR Can tolerate high current
Why join the ARRL? Since 1914 the American Radio Relay League has represented the interests of Radio Amateurs before the FCC and Congress. While there is room for policy debate, those who do not support the ARRL have virtually no voice in matters concerning ham radio. Also, the QST magazine is an excellent educational tool, full of interesting articles and fun projects.