Antenna Magic
by
Ray Jurgens
KQ6RH
(C) 1998, 1999, 2000
Updated 2/25/2000
This page is devoted to light weight wire beams and quad antennas. Most of these antennas are low profile wire beams constructed with fiberglass rods and tubes supported with central hubs. Each of these has been designed to give significant gain over a dipole but require much less space. All are self supported and able to be rotated with low cost TV antenna rotators. This site provides construction details as well as information about where specific materials can be found. We also offer some materials that are difficult to find or make.
Philosophy
You may wonder what the motivation is to try to build antennas with super-light weight structures when larger and heavier structures are readily available. Some might say that this is equivalent to buying into the minimalist movement which, for ham radio, is the same faction as the QRP movement. However, there are many reasons for developing light weight systems for portable and emergency situations as well as relatively stealth applications in controlled spaces such as apartment and town house developments. A few general principles that we have tried to abide by are that each antenna must be self supporting, must be sufficiently light in weight that a single person can easily assemble it and erect it, and that if at all possible, it should be able to give significant gain over a simple dipole. Why settle for less? This is not exactly minimalism, this more in the line of optimism.
Content
This page currently discusses quad-loops, cubic quads, Pfeiffer quads, VK2ABQ wire beams, Reflected M beams, Half Squares, X-Beams and a few simple antennas including a rotatable dipole. The Reflected M beam is a variant of both the VK2ABQ beam and the X-Beam. For a given wavelength, the Reflected M beam is the smallest of all. To compare these, I'll consider the length of the spreader required for a 15 meter antenna cut for 21.2 MHz. Though these differences are small, they are significant in that the bending of the spreader increases as length cubed for an applied force. Thus, the bending of the Reflected M spreader is reduced to 60% of that of a quad loop for a similar wire loading. The Reflected M beam is planar, takes less space to construct and can be designed with performance nearly equal to that of the two element quad. For example, a two element optimized quad might have about 7.5 dBi gain with a F/B ratio of 17 dB. The optimized Reflected M has 6.0 dBi gain with an F/B ratio of near 20 dB, though the actual rear lobes are about 2 dB poorer. The reflected M beam can be assembled and erected in about a half hour. Try that with any quad. I also give the performance of the X-Beam which is similar to and has similar performance as the Reflected M. Though the X-Beam has a good front to back ratio, the front to side lobe ratio is much poorer than that of the Reflected M. Still, the X-Beam is a great antenna that uses aluminum tubing for the radial elements and folded back wires to complete the element lengths rather than using fiberglass and wire, but the Reflected M is better in most respects.
These pages carry a copyright notice. You may make a copy of this web page for your personal use, but you may not distribute it in entirety or any part of it to others without written permission form the owner. You may, of course, pass the URL to others.
Comparing Antennas
The table below give some idea of how each antenna compares to the others. The sizes given are for a 15 meter version of each antenna. The size reported is the required length of the spreader. The impedance of some antennas depends upon several parameters, but the typical values are given below for both free space and ground mounted cases. In the case of the cubic quad, only the two element version is considered in the table. The elevation and peak gain reported are for the first or lowest lobe above an flat earth ground with average properties. For the elevation data, all antennas have their centers set at one half wave length above the ground or about 24.5 feet except for the Quick Vertical which is mounted 3 feet above the ground. The Quick Vertical uses a Hustler whip fed against a counterpoise. The Half Square antenna is actually better at suppressing high angle radiation if it is set at about 18 feet above the ground, but the data given in Table 1 is for 24.5 ft.
|
Antenna Type |
Size ft |
Z Ohms |
Gain dBi fspc |
F/B ratio |
Elev. degrees |
Peak Gain dB |
|
Quad Loop |
8.38 |
130, 125 |
3.2 |
0 dB (bi-dir) |
24 |
7.8 |
|
Cubic Quad |
8.38 |
110, 117 |
7.4 |
17.7 |
24 |
11.4 |
|
VK2ABQ beam |
8.45 |
146, 200 |
3.8 |
12.6 |
26 |
9.8 |
|
Reflected M |
7.46 |
38, 47 |
4.7 |
11.8 |
26 |
9.8 |
|
Reflected M |
7.40 |
22, 24 |
5.8 |
21.8 |
26 |
10.6 |
|
Half Square |
11.8 |
48, 50 |
4.4 |
0 dB (bi-dir) |
14 |
3.3 |
|
Quick Vertical |
8.0 |
24, 34 |
0.7 |
0 dB (omni-dir) |
24 |
-0.9 |
|
X-Beam |
9.3 |
34, 33 |
5.7 |
22.9 (deceptive) |
26 |
10.5 |
|
Dipole |
11.2 |
71, 65 |
2.1 |
0dB (bi-dir) |
26 |
7.6 |
|
Table 1 |
|
Properties of Various Antennas in Free Space and Elevated a Half Wavelength |
Inspection of the table gives some interesting insights:
The Reflected M beam has the
smaller turning radius and size
All of these antennas have respectable performance, and all can be designed with light weight fiberglass construction. So, take a look at these, and pick a winner for your application.
VK2ABQ wire beams
Reflected M beams
Quad Loops
Light Weight
Cubic Quads
Pfeiffer Quads
Half Square
Quickie Vertical
X-Beams
Dipoles
Construction
Hints
Properties of Fiberglass
Rods and Tubes
Our Products
Suppliers
KQ6RH Home Page
________
LINKS
Check Out KQ6RH's home page. This page contains much information on using
Hustler Whips in various configurations for use in mobile, apartments and town houses.
Go directly to Max Gain Systems to check out Fiberglass rods and tubes.
Check out the Northern California DX Foundations synchronized beacons.
NORTHERN CALIFORNIA DX FOUNDATION
Check out the Ionospheric propagation; the following links are useful!
NWRA World Wide Ionosonde foF2