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bases: antennas, transmission lines,
batteries, digital protocols, radio
frequency (RF) circuits and techniques,
test equipment, and the list goes on.
We’ll discover that components act a
lot differently above a few megahertz
(MHz) than they do at audio and DC.
I will show you how to install those
pesky feed line connectors so the
signal goes to the right place.
Similarly, we’ll take a look at ways
to keep RF signals from leaking out of
and getting into your equipment. In
some columns (like the one this
month), there will be an experiment
or activity you can do to gain valuable
experience and maybe even a useful
gadget. Ready to get started?
I thought so!
There is no subject better suited
to kick off a column about ham radio
technology than antennas. All forms
and specialties of ham radio share
antennas as a common part of the
station. If it’s ham radio, you can be
sure of an antenna being involved.
Actually, a lot of non-amateur
electronics also deal with antennas,
such as wireless links and mobile
In this column, I’ll introduce you
to one of the simplest antennas and
show you how to make one to use at
home — or even design your own.
Figure 1 shows the basic idea: A
vertical wire is attached to the center
conductor of a coaxial cable
connector, and several radial wires are
attached to the mounting holes of the
connector. This particular style of
connector is called a receptacle or
panel jack because it is designed to
mount on a panel and have a cable
attached to it. (Bulkhead receptacles
mount with a nut and lock washer in
a single hole, and won’t work for this
A family of connectors shares
common attachment mechanisms and
body sizes. The receptacle we’re using
here is from the BNC family. (Other
common connector families include
SMA, N, and UHF.)
The vertical wire — called an
element — is the main part of the
antenna that receives the signal. Does
the orientation of the element
matter? Yes, it does. Radio waves are
made up of an electric or E field and
a magnetic or H field that are at right
angles to each other.
The magnetic field makes
electrons move in tight little circles
which is not very useful in creating
currents that flow to a receiver. The
electric field, however, makes
electrons move in a straight line. In
this case, the antenna is designed so
the E field will make the electrons
move back and forth along the wire
element, into the coaxial cable, and
down the cable to the receiver.
The orientation of the electric
field determines the radio wave’s
polarization — horizontal or vertical.
When the antenna element and
radio wave E field are aligned, the
antenna receives the strongest signal.
The orientation of the antenna’s
element or elements determines the
FIGURE 1. Basic
the formula for the
length of the vertical
element and radials. At
least two radials are
required; four are
should be arranged
the vertical element.
20 January 2015
Your Go-To Source
for Radio Know-How –
The world’s oldest amateur
radio organization is also the
United States’ national amateur
radio institution: the American
Radio Relay League, or the
ARRL ( www.arrl.org). Usually
referred to by hams as “the League,” the
ARRL’s motto is “Of, By, and For the
Amateur.” It represents amateur radio
internationally and in Washington, D.C. to
insure that hams have the necessary
spectrum to fulfill the amateur service’s role.
Within the amateur radio community —
more than 700,000 in the United States alone
— the ARRL’s role is to educate amateurs,
support the volunteers who perform all
licensing activities, and provide training and
service activities to keep the skills of hams
sharp and ready.
The ARRL publishes an enormous
amount of technical and operating material in
whatever area of amateur radio is most
attractive to you. If you would like to explore
some of the technology resources on the
ARRL website, there is a special portal just
for you at www.arrl.org/tech-portal.
FIGURE 2. The quarter-wavelength long ground plane antenna behaves
similarly to a half-wavelength long dipole antenna with two quarter-wavelength halves. It uses a solid conductive sheet or radial wires to supply
the same effect as that of the “missing” quarter-wavelength.