HF Antennas and Propagation Beyond lineofsight Glenn Dixon

HF Antennas and Propagation Beyond line-of-sight Glenn Dixon AC 7 ZN

My first shortwave radio

My First Antenna: first signal

L-3 Antennas Just point them L-3 Propagation Line of Sight

BORING But Reliable

HF (VHF) Propagation Modes • • • Ocean Wave • Airplane reflection Ground Wave • Auroral Backscatter Ionospheric Waveguide • Lightning Scatter Ionosphere (Many modes) • Line-of-sight Earth Moon Earth (EME) • Diffraction Tropospheric Ducting • Repeaters and Satellites Meteor Scatter Sporadic E Handbook and Antenna Book are excellent Rain Scatter

Ionospheric Propagation • Main HF long distance propagation mode • Worldwide distances achievable with low power • 1. 6 -10 MHz (160 -30 meters) active at night • 10 MHz (30 Meters and higher) and above active during day • Higher bands depend on solar flux strength (unfortunately very weak currently) • Always surprises • Gray line • Dead band?

NOISE and INTERFERENCE • Atmospheric Noise • Manmade Noise • Power supplies • Motor controllers • Light controllers • OTH Radar • Military • Etc. etc. It’s getting worse! (Switching supply travails) China Supplies Rixos Turkey

It’s Not the Radio, It’s the Antenna! Two modern radios set to same frequency and modes, connected to same speaker and antenna will sound EXACTLY the same except in unusual circumstances. “Hot” Receiver? Two different antennas, however, will often have very different performance. Japan reception Hooper

Antenna Modelling

HF Antenna Modelling typically uses NEC (NEC 2, NEC 4). (Old FORTRAN program) • Includes ground effects, skin effect, can include transmission lines, multiple sources, poor conductors, etc. • Difficult to include terrain and house wiring, aluminum roofs and siding, etc. • 4 NEC 2…free software • EZNEC+ what I use…ARRL class available (? ) Antenna Book has free version • Many antennas one of several basic types • Modelling used to determine subtle differences like SWR bandwidth, etc. • Happy to model something for you.

Inputs: • • • Element thickness, orientation, conductivity, xyz position Source type and value Transmission lines Ground characteristics Segmentation Frequency band Outputs: • Azimuth and elevation plots (calibrated in d. Bi) 2 D, 3 D • SWR vs. Frequency

Some HF Antenna Rules of thumb • The bigger the better (sorta) • The higher the better (sorta) • Directional much better than ISO. • Better signal/noise • Less Fading • Can be difficult in nets, etc.

World’s Cheapest Antenna (that can transmit) This 20 M version $3. 15 in new materials. • Use what you have • End fed half wave popular with QRP’rs • My EFCF antenna

A • ½ wave dipole • Bottom ¼ wave is transmission line and counterpoise • Use what you have (zip cord, magnet wire, etc. ) Wire impedance not important. • Position point A about three feet off ground. • Bottom segment length determined by velocity factor. Others by speed of light. Not critical. • Will give good SWR over reasonable band • Fairly low radiation angle regardless of orientation. • Not sure why this is not more popular…

EFCF Antenna

What I’m having fun with: • Inflatable Antennas (dismal failures) • Kite Spar antennas • Multirotor applications • Suspend the EFCF antenna • Bigger? • Measure antennas