HF and Lower Frequency Radiation

Summary and Additional Resources

Summary

This module provided you with an introduction to HF and lower frequency transmissions. You should now have a basic understanding of these bands and the environmental factors that can affect them. The primary focus was on the HF band, because it is here that long range communications are most feasible. Please review the following objectives and go back and read over again anything you may not understand. You should also be able to answer the study questions contained on each of the pages.

Introduction to HF and Lower Frequencies

• Know the meaning of the frequency acronyms and what frequencies they refer to.
• Be able to state the advantages and disadvantages of various HF and lower frequencies compared to each other and higher frequencies.
• Have a basic understanding of the uses of each frequency range.

The Ionosphere and Sun

• Ability to describe the important layers of the ionosphere.
• Know how the diurnal cycle and solar cycle affect free electron densities.

Choosing the Right Frequency

• Be able to explain to radio operators and other technicians what controls HF propagation under normal conditions.
• Be able to explain how various environmental and engineering factors control the values of the plasma frequency, the critical frequency (fo), the maximum usable frequency (MUF), the lowest usable frequency (LUF) and the frequency of optimum transmission (FOT) and why these parameters are important to HF.
• Be able to use model predictions of these parameters to determine the best HF frequency to use for a particular situation or mission

HF Models

• Be able to obtain HF propagation models.
• Be able to run an HF model or obtain model output from the Internet.

Space weather

• Be able to explain what space weather is.
• Know what sequence of events that follows a solar flare and how HF transmissions may be affected.
• Have a working knowledge of the predictability of various space weather phenomenon.
• Be able to use the Internet to find information on current and near-term future space weather events.
  

Additional Sources of Information

The following links will lead you to further information on transmitting in HF and lower frequencies. You are encouraged but not required to explore these links. The links in the "HF Models" and "Space Weather" sections also contain a wealth of information. Links disclaimer.

ELF/VLF

Introduction To Natural Radio - VLF/ELF From LF Engineering
The World's Largest "Radio" Station Paper about Navy ELF system
Reception of Submarine Communication Systems Pictures showing submarine communications

MF/HF Links

Introduction to HF Radio Communications One of many nice sites from the governent of Australia.
Ionspheric Storms - A review A paper by M. J. Buansanto
How Storms Build in Space From the "Window to the Universe". NCAR.
Weather in the Upper Atmosphere Contains many links. University of Albany

General

Radio Frequency Communications An online "course" from Integrated Publishing.
Submarine Communications From the US Navy Military Analysis Network

This concludes the online portion of the HF and Lower Frequencies Module.

Last Update: 12/2/2003