Folding the Dipole
- Invented by Heinrich Hertz in around 1886, the half wave dipole is still one of the most simple and practical of antennas and still very much in use today. It consists of a half wavelength long centre fed conductor
- Connecting centre fed antennas, dipoles, yagis, rhombics, loops to coaxial cable, unless care is taken, it is not difficult to end up with feeder radiation resulting in power loss and the radiation characteristics changes
The Coaxial Line
- Impedance matching, Transmission Lines, Characteristic Impedance, VSWR & Mismatch and Antenna Losses
Quarter Wave Verticals
- One of the most useful antennas in the repertoire is the Marconi or quarter wave grounded vertical antenna. Its invention made it possible to halve the length of antennas, simplifying communications, especially at HF and below.
Polarization, lines of force
- While polarisation may seem insignificant compared with other considerations in setting up a communications system, choosing the right type can make significant improvement in performance.
- What you gain and what you lose.
While broadband and electrically small antennas may look attractive on the surface, they are by necessity compromises and usually donít work as well as tuned antennas.
Azimuth Radiation Patterns
- Below VHF the change in the radiation characteristics of an antenna will change considerably from frequency to frequency, making antenna selection more complicated.
HF insulation, the pitfalls
- Although insulation may seem relatively insignificant in the larger picture, on it depends the quality of your performance on air and how long you will be communicating for.
Matching Waves, VSWR at work
- When the radiation resistance (voltage to current ratio) of an antenna is the same value as the characteristic impedance of the transmission line (voltage to current ratio in the line), all of the electrical energy transmitted down the line is taken by the antenna and radiated into space in the form of a radio wave.
- In order to resonate at a particular frequency, an antenna needs to be at least one half wave length long. Antennas below a 1/2 wave are dependent on a ground system for resonance as well.
Antenna Gain on Trial
- Most people think it's a good thing to have and the more the better. However, this is not always true - and the amount of gain is often not what it appears to be. Assuming higher gain is what you need, how do you determine what will give the best performance?
When negative meets positive
- Lightning can be a serious hazard depending where you live in the world. Chances are that if you living in an area where lightning strikes are common and you have a communications antenna, it may be attracted to you.
Lightning at Sea
- Over 10% of deaths on cruising sailing boats alone at sea are caused by lightning.