User's Manual
Table Of Contents
- Table of contents
- List of figures
- List of tables
- Introduction
- 1 NGTtransceiver compliance
- 2 Installation
- 3 The handset
- 4 Getting started
- Switching on the transceiver
- Changing the screen contrast
- Changing the screen brightness
- Using the keys on the handset
- Accessing the Main Menu
- Switching scanning on or off
- Switching mute on or off
- Entering your station self address
- Listen Before Transmit Mode
- Replacing LQA information for all channels in an ALE/CALM network
- Making a manual sounding operation in an ALE/CALM network
- Selecting the best channel in an ALE/CALM network
- Making a Selective call from the Address List
- Making a Phone call from the Address List
- Making an emergency call using the emergency key
- Using a special ALE address syntax to make a call
- Appendix A— Standard hot keys
- Appendix B— Entering and editing text
- Appendix C— Finding words and values
- Appendix D— Creating an entry in a list
- Appendix E— HF radio transmission
- Appendix F— Definitions
- Index
HF radio transmission
74 NGT ASR Transceiver Getting Started Guide
Sky wave
The sky wave is the most important form of HF propagation.
The radio wave is transmitted toward the sky and is reflected
by the ionosphere to a distant receiver on earth.
The reflective properties of the ionosphere change throughout
the day, from season to season, and yearly.
Figure 7: The reflective properties of the ionosphere
Frequency, distance and time of day
The extent to which a radio wave is reflected depends on the
frequency that is used. If the frequency is too low the signal is
absorbed by the ionosphere. If the frequency is too high the
signal passes straight through the ionosphere. Within the HF
band, low frequencies are generally considered to be in the
range of 2 to 10 MHz. High frequencies are above 10 MHz.
A frequency chosen for daytime transmission may not
necessarily be suitable for night-time use. During the day the
layers of the ionosphere are thick. The layers absorb lower
frequencies and reflect higher frequencies. At night, the
ionosphere becomes very thin. The low frequencies that were
absorbed during the day are reflected and the high frequencies
that were reflected during the day pass straight through.
Summer HF communications usually operate on higher
frequencies than those used in winter over the same distance.
ionosphere
transmitter
receiver
emitted
HF wave
reflected
HF wave