Generally speaking the longer the antenna the better the range or distance. In order to achieve the best performance out of a mobile antenna it should be mounted on the highest part of the vehicle and in the case of monopole antennas (i.e.: single whip antennas requiring a ground plane!) they should be as close to the center of the vehicle as possible. This is usually impossible to do on most modern vehicles but this is what to aim for.
The best installation should be, antenna length first, height of the antenna second, then the position of the antenna last.
With base station antennas the best place for them is as high as possible and as far away from TV antennas as possible. If you do have to mount the antenna near a TV antenna then the best place is directly on top and at least one metre away. Do not place an antenna along side of anything metal such as a water tower.
With mobile antennas the best place for them is as high as possible, Do not place an antenna on the bottom of a bull bar of a vehicle as this will shield the radiation pattern and cause a bad SWR, which in time may damage your transceiver. If you are mounting more than one antenna on a vehicle they should be as far apart from each other as possible, with UHF antennas at least 350mm anything less then that the antennas will react with each other, this is not a drastic situation but may reduce the performance of the antenna and also affect the their SWR. If in doubt please ask.
Without a doubt simple is often best! If you want an antenna for local to long range nothing beats the monopole antenna, this is usually mounted on the bonnet using a bonnet mount or on the roof of the vehicle using a gutter mount. (The image on left shows a simple installation of a M474HD UHF CB antenna on a BMB bonnet mount) One benefit of the monopole is you have a very large choice of antennas that you can put onto the antenna base, ranging from as short as 300mm to as long as 1500mm. You also have the freedom of removing the antenna or changing the antenna to a different length, colour or frequency. The BMB is excellent for this type of installation as requires only a small Allen key to install and leaves no marking on the vehicle when removed, even after years of being on the vehicle.
The popular white hollow fiberglass collinear antennas what some people call "broomstick" antennas are the best performing of all mobile antennas.
These antennas are generally mounted on the top of bull bars. There are two types of these antennas, "Removable and Fixed", the Fixed antennas are the preferred antennas for performance as they have a direct connection to their internal, However a long antenna can be a nuisance when you need to get into a low roof garage or shopping centre and so the need to easily remove the antenna can be essential, plus the ability to exchange the antenna from a short to a long antenna is a real plus. These antennas are available in a large range of different lengths and springs.
The Raised Feed antennas are by far the most robust of all the UHF CB antennas and have the highest transmit gain for the shortest lengths!
There are models to suit every kind of installation from mirror mounts to bull-bars. The raised feed is a dipole antenna that has its very own stainless steel tube ground plane, They can be used with a large range of antenna tops of either stainless steel or fiberglass of different lengths and colours, So for an almost indestructible antenna with high gain, nothing beats a Raised Feed Antenna!.
The best performance you could expect for a 477MHz UHF using a 5 Watt radio and a 6dB Gain antenna is around 15 to 20 Kilometers and that is depending on the terrain as the UHF signal is line of sight (if you cannot see it you wont reach it), However UHF CB have what are called repeaters that are positioned in high areas that can greatly extend this range!
The best performance you could expect for a 27MHz CB using a 5 Watt AM only radio and an antenna at least 1.5 metres long is around 10 to 15 kilometers, However 27MHz SSB radios have a much greater range and are the preferred way to go!. 27MHz is a much lower frequency than 477MHz so has the ability to bounce or skip off the atmosphere it is known to produce extraordinary distance's, For example it is not uncommon to speak to someone in Perth when you are in Sydney (Skip conditions can be a rare event depending on many factors), This can be can be beneficial when you traveling and are away from any large population!.What is Gain ?
Simply put gain is achieved by the antennas ability to radiate its signal close to the horizon reducing the amount of signal directed upward and is usually stated in dB, this gain measurement has to be compared to something else, for example it can be dBi (over an isotropic) or it can be dBd (over a dipole) or it can be, and rarely is dBQ (over a quarter wave). Mobile One quotes our gain over an isotropic radiator, this often looks like the antenna has less gain than others but this is not the case, don't be caught with outlandish gain statements, simply put, the longer the antenna the more gain the antenna should have, An antenna with higher than 7dBi should never be used on a vehicle, as the antenna will have a too low radiation pattern to perform well, any antenna with higher than 7dBi should be used on buildings or in high altitude applications or at least be used where there are no mountains in or around the area.
It is important to note that "not every one is honest" regarding gain measurements.
SWR stands for "Standing Wave Ratio" and is the ratio of the amount of signal standing in the coax to the amount of signal radiating from the antenna. A SWR of 1.5 to 1 or better is quite acceptable.
The coax cable should be as short as possible and if In situations where the antenna is already tuned i.e.: UHF and pre-tuned 27Mhz antennas, the length is not important but still should be as short as possible.
Excessive noise can be the hardest thing to eliminate, the best advice is to contact Peter at Mobile One or your local Dick Smith Electronics store for a Noise Reduction Kit or advice as to
how you can reduce the noise, See Noise problems in "How to Tune.
How annoying when you lose the tip off your antenna! We
at Mobile One appreciate our customers need for spare bits & pieces so we will try to make it easy for you. Simply call us on 04-2535-5500. Let us know what part of your Mobile One Product you need and we will post it to you, the same day, or if you know the part you need or if can describe the part or state the code just e-mail Sales firstname.lastname@example.org