Scientific question regarding radio communications--CB radios antenna

Agent-x - May 27 2012, 8:18 PM

Based on your presenting problem I am assuming that you are a neophyte in the field of electronics especially in radio communications otherwise you would not formulate your inquire this way.
First, before I answer your question in details, I want to give you the bad news then the good news.

First, the bad news:
It is cheaper for you to buy the CB antennas than to make them if you met one or a combination of the following criteria:
1- You have a tight budget,
2- You don't have much time to spend beside your regular routines.

3- Learning basic High School physics theories are beyond your ability to grasp or appears very intimidating to you.
4- You have the capacity to learn but you careless about learning a few electronics theories.

5- You have a substantial physical impairment that may prevent you from completing the antenna construction.

The good news is:
You should be able to use available objects in your environment to make CB antennas or other radio transmitter/receiver antenna.

This will help you to keep cost very low if you have the will power, the inclination to learn simple physics theories and willing to spend few extra dollars in case you made a few mistakes during the construction of the antenna.

In addition, You will have the satisfaction
If buying the CB antenna is more convenient to you, I am going to give you a list of electronics dealers that sell CB radios and amateur radio equipments.

Belpolitik website is limited to three[3] hyperlinks, so to circumvent this difficulty, I substitute the dots by an hyphen in those links below.

Remember to replace the hyphen by a dot
ie: in the link w5qx-org/dealers-htm, replace the hyphen [-] betweern 5qx and org by a dot[.]
You may find the CB antennas at the following websites:
No matter how apparently simple an antenna may looks, its design is based on mathematical equations that go beyond the scope of this information.

That does not means you cannot make an efficient antenna if you are not familiar with basic electronics principles in radio communications.

If you follow the instructions from the experts, you should be able to make good antennae/antennas for radio transmitters and receivers that are below and above the CB band.

There is antenna theory and there is antenna reality.

Theory is a good staring point for many people and experience is important when it comes to real problems.

The knowledge gained from the best book on theory will not necessarily produce the best antenna design.

If you decide to make those antennas yourself the easy way without understand the scientific principles that underline their construction and functioning this is what you have to do:
First you could make a CB antenna with horizontal polarization if most of the users are using their CB at home but that does not mean those that have mobile CB won't be able to communicate with the base CB[Base CB is defined as CB in the house]
1-Find two 10 feet of metallic wire**
2- Find 3 pieces on insulators such as [pvc, gelatin, mica, even plastic clothes hanger]
3- Find or buy buy 50 Ohms coax cable long enough [between 25 feet to 50 feet]to attach from the center of the antenna to your radio.

The shorter the cable from the antenna to your radio the better.

4-Find two 15 to 20 feet poles or two tall trees to hang the antenna.

The antenna will look like a T after you insert the coax cable on point c1,c2


d-----e ]
a= e= tree or pole where you will attach the antenna.

b= d= insulator that will electrically insulate the antenna from the pole or the tree.
c1,2=insulator center piece that electrically insulate both side of the antenna.

line a-b & d-e could be any length
line b-c=8 feet 6 inches this length is critical and must be exact
line c-d= 8 feet 6 inches this length is critical and must be exact
c1 and c2 are the antenna polarity attached to the 50 ohms coax cable the other end of the cable should go to the CB radio.

Remember that the height of the antenna is very important.

The higher the antenna, the more miles it will covers.

Your signal will cover long distances also if your antenna is near the ocean or the soil salinity is relatively high.
** CB radios work on the 11 meter band that means the antenna length should be a total length of 102 inches long to resonate on the CB center frequency.

That is to say the left side must be 8 feet and 6 inches and the right side must be 8 feet and 6 inches
The following link will show you how a dipole horizontally polarizeed antenna looks like:
To do a vertically polarized antenna follow this link:
The above link show you a 10 meter band antennas which is designed for amateur radios but is is close in length to the CB band by a few inches.

Now if you want to learn more about radio communication to understand what you doing, read the additional info below:

If you can and willing to learn a few scientific facts about electronics communications and feel good about your knowledge then I will say it is more rewarding to make those antennas yourself and on the long run it will cost you less since you will be able to modify them or recycling them instead of buying another.

Beside dipole you will learn that there are a multitude of other antennas that you could build for radio transmission an reception such as :
Horns antennas
Horns antennas look like rectangular loudspeakers and pyramids.

They are used where high gain is needed, the wavelength is short [microwave] and space is not an issue.

Horns can be narrow band or wide band, depending on their shape.

A horn can be built for any frequency, but horns for lower frequencies are typically cumbersome and impractical.

Yagi antenna
A Yagi antenna is made of several dipole antennas linked together.

The Yagi antenna is a simple rigid dipole antenna placed horizontally, with a connection at center.

Another horizontal dipole antenna is placed at a 90-degree angle to the first wire, and shares the same connection point.

Finally, two more horizontal dipole wires are connected to the ends of the original antenna.

Yagi antennas are called directional antennas because they are very efficient at transmitting and receiving in one direction.

This makes them useful for two-way radio communications where both stations are fixed locations, such as buildings or parked vehicles.

The Yagi antenna design enables radio communication over longer distances than a simple dipole.

Random wire is a long wire any length whose length does not bear a relation to the wavelength of the radio waves used, but is typically chosen more for convenience.

A random wire are monopole antennas that are usually not as effective as antennas whose length is adjusted to resonate at the wavelength to be used. They are used mostly for temporary or emergency transmitting stations, as well as in situations where more permanent antennas cannot be installed.

Random wire antennas are a type of monopole antenna and the other side of the receive
Omni Antenna
Omni-directional antenna, is made from a dipole antenna wire that has had its two ends bent into a curved shape.

This antenna looks likes the shape of the letter "S." By bending the poles of the dipole antenna, the maximum receiving range is reduced, but nearby omni-directional signal strength is improved.

An omni antenna is used in two-way radio situations where all communication will will take place near one small area, such as a base or outpost.

The omni design allows radios in any direction near the base station to be easily reached.

Cell phone towers also commonly use omni antennas.

This enables a cell phone radio signal to reach a nearby tower from any direction, and even if the user is moving.

Parabolic Antenna
A parabolic antenna combines a simple dipole with a semi-circular dish. Just as a magnifying glass can focus light to a precise point, the curved dish reflects radio signals directly onto the dipole.

The most common example of a parabolic antenna is the home satellite dish, however the design can be used in other two-way radio applications as well.
Parabolic antennas are used for two-way communication over extremely long distances, and are usually able to transmit farther than a Yagi design.

The parabolic antenna type is only useful if the exact location of the target receiver is known.

Parabolic antennas are frequently used for two-way satellite links, long-range wireless Internet, and two-way radio communication between fixed stations.

Precaution must be taken when erecting an antenna.

Let me warning you, hundreds of CBers, Radio amateurs, electronics technicians are killed every years while installing antenna.

Some fell from the roof, tree. Some are electrocuted because their antenna are too close to high voltage power lines[ 25 feet or less] The antenna doesn't have to touch a power line for you to get electrocuted.

Just being near a power line can cause a lethal arc to your antenna.

Disconnect your antenna during lightning and thunder..

never touch the antenna when transmitting you could receive a nasty electrical jolt to say the least.

Never key up or attempt to operate your CB without a working antenna or "dummy load" (non-radiating antenna simulating device) connected to the radios antenna jack you will destroy the the radio.

Never give your name and location.

If you are on a budget buy a cheap radios and good antennas.

A good antenna on an inexpensive radio will almost always outperform a bad antenna on an expensive radio.

A good antenna is 1/2 wavelength but this is not sacrosanct.

There are many good antennas that are longer or shorter than 1/2 wavelength.

The size of the antenna is determined based on it's intended use. A quarter wavelength antenna is commonly used for mobile communications.

For use in the middle of the CB band at channel 20, a 1/4 wavelength antenna would be 9 feet long.

An antenna is an electrical circuit.

Any conductor can act as an antenna for radio waves but making an efficient or resonant antenna need expertise.

An antenna is said to be resonant when voltage and current are in phase at the antenna terminal.

When your transmitter put a current[Radio frequency-RF energy]into an antenna, your antenna responds by producing a magnetic field surrounding the antenna[this is the signal] When the magnetic wave strikes another antenna[the receiving station antenna] it induces a current on the receiving antenna surface[that current is then converted by the receiving station receiver to sound] The length of the antenna structure play an important role.

The magnetic field that your antenna puts out will produce an electric current on any metal surface that it strikes, however if the metal that the signal strikes has a length relation to itself the induced current will be stronger on the object.

When a CB signal travel through the air it complete a cycle of more or less 36 feet. If the object the magnetic wave strikes is 36 feet length [1 full wavelength] 18 feet long or[

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Jean Pierre Alexandre says...

Agent-x,i think you are confusing the man. Building a home base cb antenna is cheaper. more »

Agent-x says...

Jean pierre, Yes,it is better for the guy to buy those antennas than to make them himself because I am assuming he does not know much about... more »

Jean Pierre Alexandre says...

You are right if he does not know. I was not thinking deeply with his capabilities. Wow! you are good,I am impress with you knowledge in flow energy... more »

Agent-x says...

Do not waste your time with perpetual machine theories. The most brilliants mathematicians,physicists and chemists from many centuries have not been... more »