rf - Free and Open Source Software

Getting Your Extra
Class License
Part IV-Radio TVcLl,)es
The whole purpose of radio is to communicate,
and to do so requires that information
be transmitted from one place to be
received elsewhere. The difference between
radio and other forms of communication is
•
that, in radio, we transmit this information
over "radio waves" rather than by means of
wires or the printed page.
To use radio for communication we must
have some knowledge of the way in which
radio waves work, and so the Extra Class
license
examination includes a number of
questions to test your knowledge of radio
wave propagation.
In fact, it includes too many such questions
to cover adequately in a single installment
of this series. This month we'll look at
the general principles involved, and some of
the more unusual aspects of VHF propagation.
We'll handle the following questions
from the FCC study list :
48. How do the directivity of an unterminated
"V" antenna and a parasitic
beam antenna compare?
58. What are aurora-reflected VHF signals?
If such a signal is heard, what
does it sound like?
67. What constitutes a parasitic an tenna
element?
71 . List some different types of beam
antennas.
76. What determines the skip distance of
radio waves?
As usual, we'll extend the scope of these
questions to cover the subjects more fully.
For a start, we'll examine the whole problem
by asking "What Is Radio Communication?"
We will find, while exploring that subject,
that signals are both radiated and reflected
in the process of being used to com municate.
Our second and third questions will look
in more detail at reflection, by asking first
"How Does Signal Reflection Occur?" and
then "How Does Reflection Affect the
Signal?". The answers to these two questions
will include the unusual VHF effects, and
will also help us meet the final two questions.
OUf final two questions will bring us into
the area of signal radiation: "How Is a Signal
Radiated?" will introduce the subject of
antennas in general; "How Can a Signal Be
Concentrated?" will focus our attention on
directive antennas.
While we'll get no farther in this month's
instalment, future discussions will extend
our study of antennas in the same direction.
All set? Let's dive in.
What Is Radio Communication? It may
seem an overstatement of the obvious to
proclaim that the whole purpose of radio is
to communicate - yet many of us are so
involved with the purely technical aspects of
radio and electronics that we tend to lose
sight of this basic fact. For this reason it's
worth while to stand back at this point and
try to find out just what is involved in
communication by radio - or "radio communication".
Let's try to find out what is involved by
doing some "word substitution". What we
want to know is simply "What Is Radio
Communication?" If we can substitute other
words or phrases for the words "radio" and
"communication", we may have a meaningful
answer.
We'll tackle the hard o ne first - what can
we put in the place of "communication"?
This is hard because the question of what
constitutes communication has been stumpin&
the experts for years, and promises to
continue doing so for some years to come.
About all that they agree on is that communication
involves a "transfer of information"
- so let's try that on for size.
"Radio transfer of information" still
seems to make sense although it doesn't tell
100
73 MAGAZINE