Antennas For CB Radio

To choose the best CB antenna you will need to consider these points.

Designing and Manufacturing Antennas since 1973.

For more information, ideas and advice please see our Frequently Asked Questions

 

Australian CB Radio has two bands 477MHz UHF and 27MHz HF which one should I use?

Currently the 477MHz UHF band is the most popular CB Band, the reason for this is undoubtably the ability to use antennas that are either short that have a low gain, or long that have a high gain, (the higher the gain the better the distance) this is in contrast to the 27MHz band that requires antennas to be very long that have low gain, UHF antennas also give you a lot more choices where you can mount the antenna on your vehicle.

The 27MHz CB Band has the benefit of low frequency compared to 477MHz which make for an extreme long range ( 1000's Kilometers) during times of good atmospheric conditions or when you are in the right place at the right time on the right channel, this is called skip and is common especially around the end and the beginning of the year, 27MHz as it is less popular has many more free quiet channels. (See more below)

477MHz UHF verses 27MHz HF frequency

477MHz UHF is Ultra High Frequency, UHF radio waves will not reflect off the atmosphere but will go through it, so it is said that UHF radio waves travel at "line of sight". UHF radios require the assistance of repeaters that are located on top of mountains to extend their range!

27MHz HF is a much lower frequency where the radio waves can be it is skipped of the atmosphere and can go over mountains. They can exhibit at times amazing distances (e.g.: Sydney to Perth) due to the skipping of the radio waves of the atmosphere, but as stated elsewhere they require long antennas up to 2.6 metres or 8 1/2 feet! (See more below)

What about the new 80 Channel UHF Radios ?

                             All Mobile One UHF Antennas are very broadband and can easily cater for 80 and More Channels

Do UHF antennas need to be tuned?

                          UHF Antennas are very broadband, 10 to 15MHz in some cases, this means they do not need tuning.

Do 27MHz antennas need to be tuned?

Mobile One make a range of factory-tuned 27MHz antennas and also make a range of tunable antennas , The longer the antenna the better the performance and the less the requirement for testing or tuning (Antennas longer than 1.5mtrs need not to be tuned).

However it is always recommend you test your 27MHz antenna with the use of a SWR meter if possible. (See more below)

Where do I plan to put the antenna? Bull Bar, Roof, or Bonnet Mount?

Best place for performance is usually the center of the car roof, Gutter Mount, Front Guard, Bonnet or Bull bar - the higher the antenna the better the range.  Years ago it was popular to mount a monopole (single whip antenna requiring a ground plane) antenna on the top centre of the vehicle and these performed excellently, so do not underestimate the value of simple, EG: A S474 or M474 on a UL12C Cable on the bonnet of a car will work very well.

If you put any antenna on a bull bar you should always consider a spring to absorb vibration, this will lengthen the life of the antenna, but will reduce your choices to using either a Raised Feed Type for strength or a collinear for distance.

What do I plan to do? Highway or Bush bashing?

Highway: You can use a simple monopole on a bonnet or front guard as mentioned above this is an excellent choice if you need to remove the antenna or you want an antenna that's not expensive and might be a temporary install for the holidays, Or you can go all out and mount a more permanent antenna off the bull bar such as a collinear with high gain for long distance a SS476 or a removable CP476 antenna are good choices but remember you may need to take the antenna off in order to get into some shopping centers.

Bush: You should consider a more solid indestructible antenna such as a raised feed, these perform very well and are most popular for mirror mounts and bull bars. If you plan to use a raised feed on a bull bar than it must have a spring to absorb any vibration and if your vehicle is diesel then we recommend a large spring.

The higher the gain the better the performance.

In order to get a higher gain the antenna needs to be longer, There is no such thing as a short high gain UHF antenna. The shortest antennas that have the highest transmit gain are the Raised feed types however, their receive gain may be less than its transmit gain.

The longer the antenna the better the performance.

Long antennas have high gain on transmit as well as receive. The highest gain on a moving vehicle should not be greater than 7.5dB as antenna becomes too long and the angle of radiation too low!

The Higher the antenna the better the performance.

Where you put your antenna is most important, It should be high as possible and as far away as possible from any other antenna or obstacle.


 

Monopole UHF Antennas

"A single antenna that uses a metal area under the antenna for the ground plane"

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Monopole antennas require to be mounted onto a Base and need at least one square metre of metal as a ground plane to work effectively, this ground plane can be a Bull bar, roof, Balcony railing, any metal surface area. Monopole antennas are low profile, easy to install, they are available in various colours with either PVC (plastic) or polyolefin (rubber looking) covering.

Some Do's & Don't with Monopole Antennas

DO - Test for shorts or open circuit if possible with an multimeter or check SWR with a SWR meter. Testing the antenna ensures that all is in working order including the transceiver

DO - Mount the antenna high as possible, The centre of the roof is not always possible but it still is the best place, next best is on a "BMB" mount on the bonnet or boot lid.

DON'T - Use a spring even if mounted on a bull bar, The spring is important to absorb the vibration from the engine but will make the antenna out of phase and have a bad SWR greatly reducing the performance.

DON'T - Use a wire strap to earth the base - It may damage your radio
You must earth the antenna at the base, supplying a sufficient ground plane area

DON'T - Mount the antenna along side any metal object - As far away as possible
Any metal object will absorb the radiation from the antenna, greatly reducing its performance, you need at least 700mm from a wall or from another antenna for 477MHz antennas, if this is not possible then mount the antenna as far away from any other antenna or metal object as possible.

Warning - Do NOT use a spring under a UHF Monopole antenna
(UHF Monopole Antenna) they cannot be adjusted!

 

m474spring
UHF monopole antennas are   FDW470, S474, M474, M476 etc 

 


 

Collinear Antennas

Have their own built in ground plane

 

cp476

 

Most high gain - collinear antennas are DC Grounded and do not need tuning

DC Grounded means the antenna has what is known as a LC Network, Tuning stub or similar method for matching the antenna in order for it to work on the frequency required, what this means is that if you were to measure the connection at the base of the antenna with a ohm meter it would read a DC dead short (DC Grounded) - This is normal and is a common way of designing antennas. DC Grounded antennas do not need a ground plane or earth as in the case of monopole antennas;

Some Do's & Don't with DC Grounded Antennas

DO - Test for shorts or open circuit if possible with an multimeter or SWR with a SWR meter. When a DC grounded antenna is tested with a ohm meter the reading is a short circuit or around 3 Ohms at the base, this seems strange but it is correct!. It is important when testing the cable that the cable is not connected to the antenna or to the transceiver! If in doubt please call.

Testing the antenna ensures all is in working order including the transceiver

DO - Mount the antenna high as possible - Bull bar is often the best place for this style of antenna

DO - Use a spring if mounted on a bull bar. The spring is important to absorb the vibration from the engine, without the spring the antenna eventually may fall apart!

DO, DON'T - Earthing the antenna at its base, doesn't matter - It makes no difference to performance

DON'T - Mount the antenna along side any metal object - As far away as possible
Any metal object will absorb the radiation from the antenna, greatly reducing its performance, you need at least 700mm from a wall or from another antenna for 477MHz antennas, if this is not possible then mount the antenna as far away from any other antenna or metal object as possible.

 

 


 

Raised Feed Antennas

Have their own built-in ground plane

 

rf470ss

 

Raised Feed - antennas are very broadband and do not need tuning

What we call raised feed are really a simple dipole made up of a monopole antenna and a ground plane in the form of a 1/4 wave long tube, this tube draws the radiation pattern toward itself producing a lower angle of radiation that hugs the horizon more effectively producing extra gain. They do not need to be earthed and can be mounted any where even as a base antenna

 

Some Do's & Don't with Raised Feed Antennas

DO - Use any UHF monopole antenna top on any of the Mobile One Raised feeds e.g.: S474, M474, M475 with the exception of the M476 as it is too long

DO - Use a spring if mounted on a bull bar - Some bull bars are OK but some can severely vibrate. The spring is important to absorb the vibration from the engine otherwise the antenna will eventually fail. It extremely important that you use the correct spring in the right position

DO - Mount the antenna high as possible - Roof or Roof Gutter is the best place for this style of antenna, next best place is on the front guard

DO - Use a spring if mounted on a bull bar. The spring is important to absorb the vibration from the engine,
without the spring the antenna eventually may fall apart!

DO, DON'T - Earthing the antenna at its base, doesn't matter - It makes no difference to performance

DON'T - Mount the antenna along side any metal object - As far away as possible
Any metal object will absorb the radiation from the antenna, greatly reducing its performance, you need at least 700mm from a wall or from another antenna for 477MHz antennas, if this is not possible then mount the antenna as far away from any other antenna or metal object as possible.

 

 


 

RF Choke Antennas

A low gain low profile antenna that has its own ground plane

 

cd470

RF Choke - antennas are very broadband and do not need tuning

Mobile One make a few antennas that use the RF Choke method of matching, this is achieved by coiling the coax in a way to produce the correct matching for the frequency, they do not need a ground plane nor do they need to be earthed, These antennas are low profile and low gain but have a large bandwidth that makes them ideal for use where height and lack of ground plane is an issue.

 

Some Do's & Don't with RF Choke Style Antennas

DO - Mount the antenna high as possible - Roof or Roof Gutter is the best place for this style of antenna, next best place is on the front guard

DON'T - Earthing the antenna at its base, doesn't matter - It makes no difference to performance

DON'T - Mount the antenna along side any metal object - As far away as possible
Any metal object will absorb the radiation from the antenna, greatly reducing its performance, you need at least 700mm from a wall or from another antenna for 477MHz antennas, if this is not possible then mount the antenna as far away from any other antenna or metal object as possible.

 


 

27MHz CB Antennas up arrow

 

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To choose the best 27MHz CB antenna you will need to consider these points.

 

27MHz antennas may need to be tuned with the use of a SWR meter

Many 27MHz CB antennas are provided pre-tuned , this is usually not a problem especially with antennas longer than 1 metre, but antennas that are shorter than a metre long should be checked for a good SWR. All antennas should be tested regardless of the frequency in case of faulty base cable or connectors. See How To Tune

There Are "Cut To Tune" &"Factory (Pre) Tuned" See How To Tune

Cut to tune - These are usually tapered fiberglass types such as the (DX136SW to DX170SW) & (DX270SS) etc. These antennas require the use of a SWR meter to tune them, the advantage is that you can achieve a 100% effective output.
pre-tuned - These are usually constant diameter fiberglass antennas that such as (DX125CD to DX170CD) & (DX120FW to DX152FW) etc. These antennas do not need to be tuned as long as they have been installed correctly onto a vehicle such as a Car, Tractor, Boat, or similar, these antennas will not work as base antennas unless they are in most cases lengthened

The longer the antenna the better its Range.

The longer the antenna the better the performance and better the bandwidth, antennas under 1 metre in length are usually expected for local use!. If you want to do skip or long distant ground wave communication then the antenna must be at least 1.5metres long.

Rubber Ducky or mini antennas under 500mm long will only tune well for a few channels.

The Higher the antenna the better the Range.

Where you put your antenna is most important, It should be high as possible and as far away as possible from any other antenna or obstacle.

The Thicker The Antenna The more Broadband!

The thickness of the antenna is not generally important unless there is a need to operate on a larger than normal bandwidth
(A lot more channels)

There Are Different Types of Coating PVC Plastic or Polyolefin (kind of rubber)

PVC - A  thick coat of PVC plastic and is suitable for most applications, available in Black or White.
Polyolefin - A  thick coat of Polyolefin, for high quality & long lasting finish, available in all colours.

Where do I plan to put the antenna? Bull bar, Roof, Front Guard or Bonnet?

Best place for performance is usually the center of the car roof, roof Gutter Mount, Front Guard or Bonnet then last Bull bar - the higher the better. If you put any antenna on a bull bar you should always consider a spring to absorb vibration, this will lengthen the life of the antenna

What do I plan to do? Highway or Bush bashing?

Highway: You can use a simple monopole on a bonnet or front guard as mentioned above, this is an excellent choice if you need to remove the antenna or you want an antenna that's not expensive and might be a temporary install for the holidays. Or you can go all out and mount a more permanent antenna off the bull bar such as a DX270SS or DX270AS but remember you may need to take the antenna off in order to get into some shopping centres.

Bush: You should consider a thick antenna. Where the antenna is placed on the vehicle is important , if it is on the front guard or bonnet then you have to consider which side to put it, if you put it on the passenger side it will be out of driver view but it will hit trees, if you put it on the drivers side it will not hit any trees but will be in your view. If you put it on a bull bar than it must have a spring to absorb any vibration and if your vehicle is diesel then we recommend a large spring.

 

Some Do's & Don't with 27MHz Antenna

DO - Test for shorts or open circuit if possible with an multimeter or check SWR with a SWR meter. Testing the antenna ensures that all is in working order including the transceiver

DO - Mount the antenna high as possible, The centre of the roof is not always possible but it still is the best place, next best is on a "BMB" mount on the bonnet or boot lid.

DO - Use a spring if mounted on a bull bar to absorb vibration from the engine

DON'T - Use a wire strap to earth the base - It may damage your radio
You must earth the antenna at the base, supplying a sufficient ground plane area

DON'T - Mount the antenna along side any metal object - As far away as possible
Any metal object will absorb the radiation from the antenna, greatly reducing its performance, you need at least 700mm from a wall or from another antenna for 477MHz antennas, if this is not possible then mount the antenna as far away from any other antenna or metal object as possible.

The main causes for poor performance with 27MHz antenna Poor ground plane, Bad SWR,

Antenna too short, Antenna too low, Antenna to close to another.