Copyright 1999 by Palstar, Inc.
Used with permission
Special thanks to Paul Hrivnak, N8PH, for allowing its use here.
Radio is a way of communicating across distances without the use of wires by means of electromagnetic waves. These electromagnetic waves can travel through the Earth's atmosphere, but unlike sound waves, they are not reliant on the air to carry them. They travel just as well (or even better) through the vacuum of space.
The most basic characteristic of any electromagnetic wave is its frequency, which is the rate at which it rises from zero to some positive level, and then back through zero to some negative level and then back to zero again. One of these complete alternations is called a cycle. The number of these cycles occurring each second is the frequency of the electromagnetic wave. The unit of frequency, the cycle per second, is named after Heinrich Hertz, an early radio researcher. One Hertz is equal to one cycle per second.
Closely related to the frequency of electromagnetic waves is the characteristic known as wavelength.
As a single radio wave or cycle begins to leave an antenna, it travels outward through space. How far does it get before one cycle is completed? It travels at the speed of light, 186,000 miles per second, or in Metric units, 300 million (300,000,000) meters per second.
If we were to radiate a one hertz wave, the front edge of it would have traveled 300 million meters by the time the rear edge of the wave leaves the antenna one second later. Thus, the wavelength of a one hertz transmission would be 300 million meters or 186,000 miles long!
If we were to radiate a wave with a frequency of one million hertz, one cycle would only take one one-millionth of a second, and the wavelength would therefore be one one-millionth of 300 million or 300 meters. One million hertz can be referred to as 1000 kilohertz (kHz) or 1 megahertz (MHz). 1 MHz is located just about in the center of the standard AM broadcast band.
To calculate the wavelength of any frequency in meters, simply divide 300 by the frequency in megahertz.
With this explanation of wavelength, you can now understand what is meant when someone talks about, say, the "80 meter band" or the "49 meter band." This is just another way to refer to a group of frequencies that have been set aside for a specific purpose. For example, the 80 meter band is an amateur radio (ham) band that runs from 3.5 MHz to 4.0 MHz. The 49 meter band is assigned to international shortwave broadcasting and runs from 5.90 MHz to 6.20 MHz.
These meter designations for the
bands are chosen to be a nice round number from somewhere near
the middle of the band. The frequency of an 80 meter wave is 3.75
MHz, the frequency of a 49 meter wave is 6.122 MHz. Obviously,
some of the wavelengths in the band are shorter, and some are
longer than the length designated by the band name.
The Electromagnetic Spectrum
Electromagnetic waves have different characteristics depending on their frequency. The only difference between radio waves, the microwaves that cook your food, light beams, and X-rays, is their frequency. The Palstar R30 receives frequencies in the range of 100 kilohertz (kHz) to 30 megahertz (MHz).
At frequencies above 30 MHz (which are higher than those received by the Palstar R30), we run into the range of Very High Frequency (VHF) and Ultra High Frequency (UHF) and beyond.
We will discuss later what you can
expect to hear on these different frequencies.
Propagation refers to the way radio waves travel through the air. When radio waves leave an antenna, some of them travel close to the ground. Receivers close to the antenna receive these ground waves directly. The range of ground waves is limited. The closeness of the waves to the Earth means that the Earth absorbs some of their energy, and farther away from the antenna, the Earth curves downward away from the straight-traveling waves, and the waves pass too high overhead to be received on the ground. To receive radio waves at longer distances, some other mechanism is needed.
The upper atmosphere of the Earth contains layers of electrically charged or ionized gasses. These ionized layers are caused by the action of light and energy from the Sun on the atmosphere. The ionized layers act as reflectors of radio waves, causing them to bounce back toward the Earth. By bouncing back and forth between the Earth and the ionized layers, it is possible for radio waves to travel all the way around the world. This is called sky wave reception.
The study of shortwave radio propagation is a scientific discipline in itself, but, fortunately for us, it can be simplified. Because the nature and location of the ionized layers in the atmosphere are caused by the action of light and energy from the Sun, it is easy to understand that the differences vary between day and night, and between summer and winter.
During the day, and more so in summer when the days are longer, the radio reflective ionized layers are at higher altitude, and the maximum frequency that the layers will reflect (called the Maximum Usable Frequency, abbreviated MUF) is higher.
At night, and more so in the winter when the days are shorter, the reflective layers are at lower altitudes, and the MUF is lower. Frequencies in the lower VHF range and higher usually penetrate right through the ionized layers and are only able to be reflected under rare conditions.
The basics of shortwave radio propagation can be summarized in a few statements:
The most common inhabitants of this
range of frequencies are navigation aids known as non-directional
beacons. They transmit at low power (usually 100 watts or so),
and their signal consists of a two or three letter identifier
repeated over and over in Morse code.
The lower end of this range, from 300 kHz to 540 kHz, was once the mainstay of ship to shore communications, mostly in Morse code. As ships have increasingly switched to high-tech satellite communications, there is less and less activity here. Many official agencies such as the Coast Guard have even abandoned their round the clock monitoring of the old international distress frequency of 500 kHz.
The main band of interest in this frequency range is the Standard AM broadcast band which runs from 540 kHz to 1700 kHz. The higher power stations can be heard over large areas at night.
MW is also home to one Amateur
Radio band, the 160 meter band from 1600 kHz to 2000 kHz.
The primary bands of interest in
the Shortwave (SW) spectrum for most listeners are undoubtedly
the international broadcast bands. They are as follows:
|Frequency in kHz||Band Name|
Everyone is familiar with standard AM and FM stations, which occupy a single frequency and broadcast on it every day. The biggest difference that you will notice between those standard broadcast stations and shortwave broadcasters is that shortwave stations move around a lot. Because the target audiences of shortwave stations are located all over the world, shortwave broadcasters transmit on frequencies and at times chosen to have the best chance of reaching the target audience at the correct time of day. In addition, these frequencies are often changed with the seasons to take advantage of the seasonal changes in propagation.
Another difference is that there is
more day-to-day variability in the reception of shortwave
stations. Because the stations are located so far away, often on
another continent, reception is totally dependant on the
condition of the atmosphere between the transmitter and your
receiver. There will be some days when your favorite station will
be very weak or not heard at all.
The Amateur Radio (Ham) bands are occupied by ordinary people from all over the world who have been licensed by their governments to engage in two-way radio transmissions as a hobby. Whenever there is a natural disaster such as a tornado, hurricane, earthquake, etc., the Ham bands are the place to listen. It is common for Ham radio to be the only communications link into or out of a disaster area for many days after the occurrence. In fact, the ability of Hams to provide emergency communications is one of the primary reasons Ham radio exists.
The primary modes heard on the Ham bands are CW (Morse code, usually down at the lower end of each band), and voice communications in the form of Single Sideband (SSB, there will be more about SSB later on). There is also a smattering of other modes: radio teletype, slow-scan TV, and other data communications methods. These signals require the use of special decoder devices or computers with special decoding software in order to read or view them.
The Amateur Radio bands are as
|Frequency in kHz||Band Name|
|10100-10150||30 Meters (CW/Data only)|
|24890-24990||12 Meters (Shared with Fixed Service)|
The Shortwave spectrum is also home
to many other radio services, including ship-to-shore,
transoceanic airlines, government, military, and others. Often
called "Utility Stations" or "Utes" for
short, their transmission modes include CW, AM voice, SSB voice,
radio teletype and data. The monitoring of Utes is a specialized
and rapidly changing area of the SWL hobby. It is beyond the
scope of this guide to provide more details, but there are books,
magazine columns, newsletters, and Internet news groups if you
want more information.
Let's say you want to listen to a BBC newscast at 5pm. But, is that 5pm in London where the program originates, 5pm in Southeast Asia where the BBC relay transmitter is located, or 5pm in New Zealand, where the intended audience lives?
To eliminate such problems, shortwave broadcast schedules are kept in World Time. World Time is the local time at the Prime Meridian, zero degrees of longitude, which runs through Greenwich, England. In the past, World Time was known as Greenwich Mean Time, today it is usually called Coordinated Universal Time, abbreviated as UTC. The military designates UTC with the letter "Z" and refers to it as "Zulu", which is the phonetic pronouncer for the letter "Z."
UTC is a 24 hour clock and the times are written in four digits with no punctuation. Thus, midnight is 0000 hours, 1pm is 1300 hours, and so on.
To convert UTC to local time, you will need to know how many time zones you are located east or west of Greenwich, England. If you are located east of Greenwich, you add the number of time zones, west of Greenwich you subtract the number of time zones. Also, you need to remember that UTC never goes on Daylight or Summer Time, so your offset will be different between summer and winter if you live in an area that sets the clocks forward in summer.
One of the quickest ways to find the current UTC time is to listen to a station such as WWV in North America. WWV announces the UTC time every minute, and transmits on standard frequencies of 2.5, 5, 10, and 15 MHz.
You may find that having a clock
that can be left set to UTC will make it easier to figure out
when your favorite shortwave program is on. There are several
low-cost 24 hour digital clocks available from suppliers who
cater to radio buffs.
CW (an abbreviation for Continuous Wave) or Morse code reception requires a bit more doing than listening to AM voice transmissions. A CW transmission is simplicity itself -- a transmitter is switched on and off by a telegraph key in the pattern of the dots and dashes of the Morse code. However, if you tune in this signal in regular AM mode, all you will hear is a kind of intermittent raspy noise as the dots and dashes go by. To convert the CW signal into a pleasant audio tone that is easy to read, there is a circuit in the receiver called a Beat Frequency Oscillator (BFO). The BFO creates a signal that is mixed with the received signal with just enough frequency offset to result in the audio tone.
In the Palstar R30, the BFO is
engaged by choosing the Upper Sideband (USB) or Lower Sideband
(LSB) modes. As you tune across a CW signal, its pitch will
change, and you tune until the pitch is most pleasing to your
Single Sideband (SSB) is a mode that provides the benefits of reduced bandwidth (thereby taking up less room on the radio dial) and greater efficiency in the use of transmitted power (thereby allowing the signal to effectively reach further without increasing transmitter power). The cost of these improvements is the requirement that the receiver have a Beat Frequency Oscillator (BFO), and tuning is somewhat more difficult. SSB is widely used by Hams, Utility stations, the military, and even some shortwave broadcasters.
Here is a brief explanation of what SSB is: a radio transmitter is tuned to the frequency it is to transmit on, called the carrier frequency. The desired audio signal (voice or music) is mixed with the carrier frequency in a process called modulation. The result is three frequencies: 1) the original carrier frequency, 2) an upper sideband consisting of the carrier frequency with the modulating signal added to it, and 3) a lower sideband consisting of the carrier frequency with the modulating signal subtracted from it.
All of the information to be transmitted is contained in each sideband. Once sidebands are generated, the only purpose the carrier serves is to provide a reference for the receiver to use in recovering the audio from the signal. If you strip away one of the sidebands and the carrier, what is left is a Single Sideband signal. Feed it to an antenna, and it will go out over the air just like any other radio frequency signal. Either the Upper or the Lower sideband can be used.
A regular AM receiver cannot properly process an SSB signal without the carrier to use as a reference. If you try to listen to an SSB signal in AM mode, you will hear a highly distorted sound, often described as sounding like "Donald Duck." To hear the audio a local replacement for the carrier is provided by the BFO.
The "USB" and "LSB" mode buttons on the front of your Palstar R30 are pre-tuned and optimized BFO settings for the reception of Upper and Lower Sideband signals. You must choose the correct one: listening to USB in the LSB mode or vise versa will result in more distortion. To avoid confusion over which to use, Hams by agreement use LSB on 160, 80, and 40 Meters, and USB on the bands above that. Shortwave broadcasters tend to use USB.
Having chosen the correct USB or
LSB setting, as you tune across a SSB signal the audio pitch will
change, and you will reach a point where the voice becomes
understandable, and it finally will reach a normal sounding
pitch. If you continue to tune past, the pitch will again begin
change, until the signal is unintelligible again.
Previously we talked about the relationship between frequency and wavelength. Antennas work best when their length is a significant fraction (i.e. ¼ or ½) of a wavelength. That means that an antenna gives its ideal best performance on only one frequency. Since the Palstar R30 receives from 100 kHz to 30 MHz, the range of wavelengths it covers is from 3000 Meters to 10 Meters, so no single antenna can give optimal performance on all frequencies.
Fortunately, receiving antennas are less demanding than transmitting antennas, and adequate performance can be had with quite simple arrangements. If you live in an ordinary frame or brick home, surprisingly good results can be had with a wire strung around the walls of a room. Generally, longer is better (within reason). After stringing the wire where it will be out of the way and no one can trip over it, just strip 1/4" (10 mm) or so of the insulation from one end. Connect the stripped end to the Red terminal on the antenna terminal block on the back of the R30. The wire can be simple 22 gauge insulated hookup wire. If you don't have a metal roof, effective wire antennas can also be strung in attics.
You may desire the improved
performance that an outdoor antenna provides, or, if you live in
a steel reinforced or metal-sided building, it may be too
shielded for an indoor antenna to work well. Performance of an
outdoor antenna will be improved by providing an earth connection
to a ground stake. The ground stake is also needed for connection
of a lighting protection device. For best results, get a good
quality ground stake that is approved for grounding an electrical
service entrance, and drive it at least 8 feet into the earth.
The wire used in an outdoor antenna needs to be strong enough to
support its own weight, as well as to hold up any additional
weight such as ice from an ice storm. Normally, 14 gauge or
larger is considered an adequate size, especially if the wire is
copper-clad steel especially designed for antenna use. If the far
end of the antenna is supported by a tree or other support that
sways in the wind, a pulley and weight arrangement will prevent
the swaying from putting additional strain on the wire.
Safety Warning: whenever putting up an outdoor antenna, you must be certain that it is located such that the antenna cannot fall across a power wire, or that a power wire cannot fall across it if either the antenna or power wire should happen to come down.
provision for protection from lightning must be provided. Even
the best lightning protection system will not protect your radio
from damage by a direct strike. To protect your radio, it is best
to disconnect the antenna and AC power adapter from the radio
when it is not in use, and do not use your radio during
Copyright 1999 by Palstar, Inc.
All rights reserved. Do not distribute or post on the Internet
without the express written permission of Palstar, Inc.
Used with permission
Special thanks to Paul Hrivnak of Palstar for allowing its use here.
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