Technical Blog

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Wire Antennas - Dipole

The following Dipole description was taken from the General Class license manual, pg 7-2 and 7-3 with permission from the ARRL.

“Dipoles are the most fundamental antenna.  It is a straight conductor that is ½ wavelength long with its feed point in the middle.

A dipole radiates strongest broadside to its axis and weakest off the ends as shown in the diagram below.  The current in a half-wave dipole is highest in the middle and zero at the ends.  Voltage along the dipole is highest at the ends and lowest in the middle.

The feed point impedance (the ratio of RF voltage to current) of a center-fed dipole in free-space is approximately 72 ohms, but it varies widely depending on its height above the ground.

In free space, ½ wavelength in feet equals 492 divided by frequency (f) in MHz.  At resonance, a ½ wave dipole made of ordinary wire will be shorter than the free-space ½ wavelength for several reasons.  First, the physical thickness of the wire makes it look a bit longer electrically than it is physically.  The lower the length-to-diameter (l/d) ratio of the wire, the shorter it will be when it is resonant.  Second, the dipole’s height above ground also affects its resonant frequency.  In addition, nearby conductors, insulation on the wire, the means by which the wire is secured to the insulators and to the feed line also affect the resonant length.  For these reasons, a single universal formula for a dipole length, such as the common 468/f, is not very useful.  You should start with a length near the free-space length and be prepared to trim the dipole to resonance using an SWR meter or antenna analyzer.”

The ARRL web site has a nice “For the Beginner” article on how to build a dipole. 

You can find it at 

And, of course, you can find most anything on the Internet.  Here’s one

Joe Eisenberg K0NEB Kits

January 20, 2017, Joe Eisenberg K0NEB, will be our Tech Demo presenter.  Joe is well known for his kits.  If the weather is bad, Joe will join us via Skype.  If the weather is good, he may drive down from Lincoln, NE., and be here in person.  If he arrives in person, he will bring a few kits to put together, so brush up on your through-hole soldering.


Most people remember seeing Joe waring the very tall red and white striped “Cat in the Hat” hat at Dayton. Joe has been licensed since 1969 and is the CQ magazine’s Kit Building editor.  His day job is an I.T. Field Technician where he fixes broken printers. If you want to know more about Joe, please check out several articles on YouTube like,


If you’re into kits, you might want to check out these web sites.

Antenna Calculators
Antique Electronic Supply
Carl’s Electronics
Chassis Kits & antennas
Communications Concepts
Crystal Radio Supply
CW Keyer/Reader Kit
Dan’s Small Parts and Kits
Down East Microwave
DZ Company, The
Electronics USA
FAR Circuits
Fox Delta
Hendricks QRP Kits
HF Projects
Idiom Press (Electronic Keyer) 
JAN Crystals
Kits and Parts Dot Com
Milestone Technologies
N0XAS HamGadgets
North Country Radio
Ransey Electronics
Small Wonder Labs
Solar Power Kits
Spectrum Communications
Xtal Set
RC Electronics LLC

Evaluation of Test Equipment Apps

Keuwlsoft Sig GenThis evaluation of smart phone bench test equipment applications highlighted several options for low cost test equipment.  As the article notes it's always a trade off between cost and your expected results.

Smart Phone Bench Test Apps

I have "Keuwlsoft Dual Channel Function Generator" running on my Android tablet. It seems to provide a basic source of audio frequency test signals.

Design Tools

Digi Key design toolsFree Design Tools from Digi-Key

An online tool for CAD, Schematic Drawing, Circuit Simulation...