HAM ANTENNAS A PRACTICAL INTRODUCTION TO THEORY AND

HAM ANTENNAS: A PRACTICAL INTRODUCTION TO THEORY AND OPERATION OF ANTENNAS BY K 0 YY

ANTENNA PRESENTATION OUTLINE • Basic Antenna Theory/Terms • Antenna Specifications • Types of Antennas • References • Summary

ANTENNA REFLECTED POWER/SWR • Antenna Fact: Antennas must radiate the transmitters power to be effective. Any power reflected back towards the transmitter is lost and may damage the transmitter. • Standing Wave Ratio (SWR): SWR is a measure of impedance matching of an antenna to the characteristic impedance of a transmission line. The perfect impedance match is 1: 1 or for example 50 ohm to 50 ohm. Operationally up to 2: 1 or even slightly higher is acceptable for short periods. • SWR is a measurement of how effective the antenna is radiating power on a given frequency. SWR increases as the transmitter is tuned

ANTENNA BASIC THEORY/TERMS • Feed Point Impedance/AKA Radiation Resistance– Varies by type of antenna, typically “matched” to 50 Ohm impedance to use 50 Ohm feed line to match the 50 ohm output of radios. • Resonant Frequency— Each antenna has a “resonant” point based upon length/element diameter– It is where the most power is radiated. Resonance basically is the point where the SWR is minimum. Half Wave Dipole Formula: Length in feet = 468/F (MHz). Example: 40 meter dipole = 468/7. 250 = 64. 55 or 64 feet 7 inches total length. Therefore each side of the dipole =

• Antenna Bandwidth– Is the frequency coverage of an antenna where the reflected power/Standing Wave Ratio (SWR) is below the lower and upper 2 to 1 points on an SWR curve.

• Take Off Angle– The main lobe of radiation above the horizontal plane measured at a specified height above ground. Dipole = ~30 degrees, Vertical = ~10 degrees. Horizontal Yagi = ~30 degrees. • Beam Width– The actual ½ power path of radiation from a beam style antenna, varying based upon the number of elements. Example 3 -element Yagi = ~35 degrees wide

ANTENNA SPECIFICATIONS Antenna Gain is Specified in decibels (d. B). See also next chart. • d. Bi = Decibel gain compared to an Isotropic (point) theoretical source. • d. Bd = Decibel gain compared to a Dipole • Antenna Fact: Every 3 d. B of antenna gain doubles the Effective Radiated Power (ERP) of an antenna. • ERP Power is a real power gain, (focused in the forward direction for a beam style antenna, and towards the horizon in a vertical colinear type antenna).

ANTENNA TRUTH TABLE-- BILL ORR HANDBOOK

TYPICAL TYPES OF ANTENNAS VHF/UHF ANTENNAS-- See examples on the tables • Verticals– • Ground Plane– Typically ¼ wave or 5/8 wave size element • Colinear-- multi-element In-line, for added gain • Multi-element • Yagis • Quads • Quagis FM versus SSB Polarization-- FM = Vertical, SSB =

TYPES OF VHF/UHF ANTENNAS MOBILE ANTENNAS • Verticals/Whips— Single/Multi-band -- Ground Plane versus Colinear (In-line for added gain) • Quad Loops– Typically horizontal loops used for 2 & 6 meters BASE STATION ANTENNAS • Verticals-- Single/Multi-band, Ground Plane versus Colinear • Dipole • Yagi Beam • Quad Loop FM VERSUS SSB • Polarization– FM = Vertical, SSB = Horizontal

TYPES OF HIGH FREQUENCY ANTENNAS MOBILE ANTENNAS • Verticals/Whips— Single band– center coils, helical wound • Multi-band– tapped, screwdriver BASE STATION ANTENNAS • Verticals– single or multi-band • Long-Wire (non-resonant and requiring a tuner or matching circuit) • Dipole- single or multi-band • Yagi Beam-single or multi-band, Tri-banders popular, • Delta or Quad Loop, Quad formula = 1005/ f (MHz) = length in feet 40 meter Delta loop = 1005/7. 250 MHz = 138 feet 6 inches

ANTENNA REFERENCES • ARRL Antenna Handbook • e. Ham website-- WWW. e. Ham. net/articles • Low Band (160 meters) DXing Book • ITS HF Propagation Software • CQ Magazine Articles • QST Magazine Articles • EZNEC Modeling Software-- https: //www. eznec. com/eznec. htm • Many Antenna Handbooks for various

SUMMARY • Basic Antenna Theory is not complex. Advanced theory is complex using physics principles and requires extra study. • Knowing basic antenna theory can help you select the proper antenna for what you want to accomplish. • Beam style antennas help you talk and hear further than standard verticals or dipoles. They focus power in the forward direction. • Colinear (stacked) antennas provide gain by focusing radiation towards the horizon (away from the vertical plane). • Understanding antenna characteristics such as resonance, bandwidth, and beam-width will help you in your operations.