On this page I will put up plans, diagrams and schematics of circuits and antennae for HAM radio.
Above is a classic example of a dipole. Usually the length is cut by this formula - 468/f = ½ wavelength - this is for the whole dipole, divide this by two to obtain the length of each leg. Cut the leg longer than needed as you will have to trim to obtain the best match. The orientation can be horizontal, vertical or inverted "V". the feedline can be 50 ohm coax or even ladder line, the most common is coax. Impeadance at the feedpoint is about 150 ohms.
The antenna above is an example of a "beam" or Yagi. This is a directional antenna and has gain in the front direction with rejection from the back. Other directional antennae are Quads, Corner Reflectors and Parabolic Reflectors. All have gain in a given direction and can have as few as two elements or as many as 20 or more! Feedlines are generally coax but the feed points can be of a dipole arrangement, but more common is a gamma or a beta feed. The latter is impeadance compensated by a matching device like a tuning capacitor or coaxial balun. Beam antennae are used from 80 meters (big!) to 1200 MHz. Parabolic reflectors are generally used at 440 MHZ and higher.
Last antenna above is an example of a ground plane. The general form is like a dipole but has three or more "ground radials" and is configured like an upside down "Y". The ground radials bring the radiating signal "flatter" and in turn this keeps the radiation pattern level to the ground. This makes a more efficient pattern for ground wave contacts. This also is useful for moble use with a magnet mount or "clip" mounts. Gain can be achieved through the use of L/C networks and these are called loading coils. Effectively making a longer antenna in a shortened space. 1/2 or 5/8 wave antennae make use of loading coils and impeadance matching can be enhanced by the use of toroids. ¼ wave ground planes are very easy to build and very gentle on the pocket book!
On this page I will put up plans, diagrams and schematics of circuits and antennae for HAM radio.
