477MHz UHF CB Antennas

Click here to go to Mobile One's range of 477MHz UHF CB Antennas

Mobile One UHF CB antennas have a bandwidth 468MHz ~ 482MHz unless otherwise requested

You need to consider

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 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.

UHF antennas do not need to be tuned.

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

When deciding on an antenna You need to ask these questions!

Where do I plan to put the antenna, Bullbar, Roof, or Front Guard?

Best is usually the center of the roof, roof Gutter, front Guard then bullbar - the higher the better. If you put any antenna on a bullbar you should
consider a spring to absorb the vibration, this will lengthen the life of the antenna.

the longest antenna that I can cope with?

Length matters , but if you require an antenna that is short but has a reasonably high gain then I suggest the "RF470 Range"
these are approximately one metre long and have 6dB transmit gain.

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

This will determine weather the antenna should be S/Steel or fibreglass

There are two main types of UHF antennas

Monopole & Ground Plane Independent

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

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 may either PVC (plastic) or polyolefin (rubber) covering.

Some Do's & Don't's 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 - Gutter mount or roof is best Centre of the roof is not always possible but it still is the best place, next best is on a "BMS" or "BMB" mount
Don't -	Use a spring even if mounted on a bullbar - *It may damage your radio* The spring is important to absorb the vibration from the engine but will make the antenna out of phase 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.

Ground Plane Independent Antennas
"A single antenna that has its own in built simulated Ground plane"

Ground Independent Antennas

There are three types of ground independent antennas
DC Grounded, RF Choke & Raised Feed

DC Grounded

Most high gain - high performance 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's with DC Grounded Antennas

Do -	Test for shorts or open circuit if possible with an multimeter or check SWR with a SWR meter NOTE- When the antenna is tested with a ohm meter the reading is 0 Ohms at the base *Testing the antenna ensures that all is in working order including the transceiver*
Do -	Mount the antenna high as possible - Bullbar is often the best place for this style of antenna
Do -	Use a spring if mounted on a bullbar. 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 real 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

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's with RF Choke Style Antennas

Do -	Mount the antenna high as possible - Roof or Roof gutter is best for this antenna
Do & Don't	Earthing the antenna at its base, doesn't matter - It makes no real 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
Raised feed antennas can be used in any and all applications including base station

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.

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

Do -	Use a spring if mounted on a bullbar - 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 bullbar. 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, does not 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.