4 Element Yagi Building

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4 Element Yagi Building

This article contains discussion of all the different antenna principles previously described elsewhere on this website. A thorough reading and understanding of the other sections are necessary to comprehend all the terms used on this page. It is not necessary to understand all the terms and theories described to build and enjoy this 4 element Yagi however. This particular section is geared towards the “freeband” CB operator – that is one who uses CB channels above (or below) the standard 40 CB channels. These CB “channels” are not legal for use in the United States – but they are quite popular any ways! The frequencies mentioned in this article are legal CB channels in some countries, check your local laws and act responsibly. This article shines little light on finding cheap aluminum or alternative methods of construction materials for Yagi antennas. It is also devoid of information on the physical design of Yagis. Sad but true, useable aluminum tubing in small quantities is expensive. And the physical design of Yagis is a subject beyond my limitations! What this article does do is provide a truly optimized 4 element Yagi design for the 11 meter “freeband” DX operator. Careful consideration was given the operating frequency and “rejection” needs of most 11 meter freeband DXers (CB operators who communicate with other CB operators more than 150 miles away). Continue reading→

Building a 4 Element Cubical Quad

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Building a 4 Element Cubical Quad

There are many reasons you should considering building your own antenna. First you can taylor it to the needs of your communication (local or DX and optimize it for the frequency you talk on) and to the needs of your environment (make it strong if you live in a harsh one where ice and wind is a problem). There is the extra part of knowing you did it yourself. To the best of my knowledge, only one company is producing a commercially available quad (Signal Engineering, Hy-Gain did) in the U.S. Another reason that you might build is you might be able to build a beam more cheaply than buying a commercial one (do not be surprised how much more you might have to spend to complete the project than you anticipated however). I assure you, there is nothing like stomping locals on DX contacts. Until your friends catch on and start building their own too (and co-phase them). Continue reading→

Performance Tips – Earth Ground

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Earth Ground

Most of us overlook the importance of hooking good earth grounds to our antennas and our radios. Some think if lightning hits, its going to do what it wants to do. Probably right! Lightning protection is not why I am stressing the earth ground. Good earth grounds serve two purposes. One they protect against lightning (by routing current to the ground instead of our radios). Secondly, they discharge stray RF energy. There are a few things this does for us. First, it makes our receiver quieter (less static). Secondly it prevents RF from building up on the station equipment and distorting our audio (So many CBers have this problem!). Have you every heard someone who’s audio would distort when they would talk? The number one cause of this is strong RF currents running on the radio chassis and mic (more power and the problem gets worse!). Also grounding stray RF energy cuts down on interference to TVs, Phones etc. Plus, if you are using a vertical antenna (1/2,5/8 Wave) you can improve the performance by lowering the angle of radiation by using ground rods and radials running on the surface of the earth under your antenna. This is a total must if you are co-phasing verticals.

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Antenna Performance : Angle of Radiation

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Angle of Radiation

Most of us think that our antenna’s “shoot” the signal straight off the end (if its a beam), at right angles from the antenna. I have even seen some operators (mainly ones who live in valleys) bend their mast so that their antenna does not sit with the boom parallel to the ground (don’t do it, read on). They hope to shoot the signal up out of the valley. Well, this is not how things work. The angle that the signal comes off the antenna, is mainly controlled by how high the antenna is from the ground. This angle that the signal takes off the antenna is sometimes called the “Angle of Radiation” or “Take-Off Angle”. You can see what I mean by take off angle by looking at figure 1. Most of you probably thought the signal came off at a 0 (Zero) degree angle, right? You would have to have your antenna over 500 feet in the air for this to happen! Continue reading→

Antenna Performance : co-phasing

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Co-Phasing

Co-phasing or “stacking” has long been a way to get high gain from antennas. Co-phasing involves placing two (or more!) identical antennas either side-by-side or one over top another (“stacking”) at a certain distance apart (usually a 1/2 Wavelength or more) and feeding the antennas in-phase. The result is 3 db more than just a single antenna. In my opinion, this is the absolute way to go with beam antennas instead of going with say, 8 elements beams, it would be much better to go with co-phasing two 4 element beams. If you look at the gain figures for a 8 element beam, you see that you will end up with more gain if you co-phasing 4 elements instead. If you are considering co-phasing antennas for your mobile, better check out the “Mobile” section first.

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Antenna Performance: Circular Polarization

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Circular Polarization

Circular Polarization is a relatively untalked about subject on 11 Meters, perhaps this is the first time you have ever heard of such a thing. Most antennas are oriented to produce linear polarization – either horizontal or vertical polarization. Sometimes, a creative CBer will turn their beam at a 45 degree angle, half-way in between horizontal and vertical polarization. This results in a signal that is weaker than if the owner would have oriented their antenna the same (polarization) as their neighbor’s antenna. This is still a “linear” polarization.

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Omnidirectional antenna

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Omnidirectional Antennas

“Omnidirectional” is generic term for an antenna that radiates equally well in all directions. There are several antennas that are considered omnidirectional.

1/2 Wavelength Vertical

Most folks lump all vertical omnidirectional antennas into the same category and call them “Ground Planes”. A ground plane antenna is actually an antenna similar to the vertical dipole.It’s important to understand the difference – especially if you’re looking to invest in a certain type. Whether you’re after antennas or Mobile Broadband deals, misinterpretations usually end badly. Shown in figure 1, you can see the hollow tubing is now instead brought out at a 45 degree angle (and split into 3 sections) out from where it is on the vertical dipole. These rods are usually called “radials”. This type of antenna is really not a very high gain antenna. Continue reading→

Coax Basics

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Coax Cables

Most CB and HAM radio operators use coaxial (coax) cable to feed their antenna. Another name for the cable you use to hook your radio to your antenna is “feed line”. Feed line is a generic term for all types of cable including coax. Coax has been around for a long time and became very popular with Radio Amateurs after World War II, when army surplus stores were filled with miles of coax cable. This is one of them main reasons why we use coax today, it became such a trend of sorts. Coax cable consists of two concentric wires, as shown in figure 1. It is important to note that coax cable is unbalanced, no current flows on the outside shield of the cable. This is in comparison other types of feed line that are balanced such as twin-lead, which you may be familiar with from your old TV antenna. Figure 1 shows a close up of the end of coax, and its makeup.

Figure 1 – Close up view of coax.

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Antenna Basics

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Antenna Basics

Radio Waves

Radio energy waves are waves of energy that are similar to light waves. In fact signals (radio waves) travel through the air at the speed of light. To understand how an antenna works you must first have a basic idea of the makeup of a radio wave. A radio wave can be visualized as a sine wave, shown in figure 1. The distance a wave travels to complete one cycle is known as the wavelength of the signal. A CB signal completes a cycle as it travels through the air at roughly 36 feet. For every 36 feet the wave travels it has completed one cycle. Since we have defined wavelength as the distance a wave travels to complete one cycle, we now know that one wavelength on CB frequency is approximately 36 feet. So, radio waves are similar to light? What is the wavelength of visible light in feet? Smaller than two inches! Figure 2 show the relationship of CB frequencies to other bands. Continue reading→

Directional Antennas : Cubical Quad

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Directional Antennas

An antenna is known as “directional” if its pattern strongly favors a certain direction. A directional works by concentrating the signal in one direction at the expense of other directions. Also known as the “Beam” antenna.

Read the section on Yagi antennas if you are not familiar with directional (“beam”) antennas and how they work. Since the Cubical Quad works off the same principles, you must first understand the Yagi antenna. Continue reading→