As with coax, it is easy to either overlook the importance of a good antenna or become mired down in all the nuances each type of antenna provides. Detailed antenna theory is not going to be covered by Axles and Antennas. With that being said, antenna selection is just as equally important as coax and in some ways, even more important than the radio. If you purchase an antenna based on price point without given a second thought to performance, chances are you are going to have a difficult time talking to your trail buddies.
Since we are affixing the antenna to the outside of the vehicle, you will need to take flexibility into consideration. A harmless looking tree limb is going to going to wreak havoc on your antenna if it is not sufficiently flexible. If you do go with a rather stiff antenna, make sure you put a spring loaded base on the bottom. This will, however, affect the overall transmitting length of the antenna. In turn, you may need to adjust the length of the antenna if your SWR reading is beyond 2:1.
Speaking of antenna length, you want to put the longest antenna feasible on your vehicle. Popular among all lengths is what is referred to as quarter (1/4) wave antenna. For a CB, this is about 108 inches, while a 2 meter ham band ¼ wave is a little over 1.5 feet. The antennas are even shorter for the UHF bands. In fact, there are lots of options for a combination VHF/UHF antenna for the dual band ham radios that operate VHF and UHF. These antennas are typically no more than a 2 or 3 feet in length. There are many other types of lengths such as 5/8 wave and the like, but is outside the scope of this discussion.
Now, take that consideration of length into how tall your vehicle is. If you mount your antenna way up high, you are going to look like the DeLorean in Back to the Future and wind up scraping every low hanging tree branch on the trail along with turning heads at the local drive though when you bang into the “max height” sign.
When researching antennas, you will undoubtedly come across the term “gain”. This can be some really pie in the sky stuff and refers to how much potential it has to be better or worse than a theoretical antenna. It is of the opinion of Axles and Antennas that this is a bit of chasing rate of diminishing returns and paying extra for an antenna that has the theoretical potential of being better is not warranted.
Mounting your antenna basically comes in two flavors: magnetic mount or fixed mount. Fixed mount is regarded as the better choice. You have better metal to metal contact for the ground section of the antenna. The coax tends to be better as well. Magnetic mounts afford you’re the ability to pick up and go which is extremely helpful if you are operating a walkie-talkie. They will pop off if you hit something hard and will very likely roll around on the surface afterwards causing some scratching.
Antenna placement is always, always going to be a compromise of convenient location versus perfect location. As it stands, placing an antenna on a vehicle is never going to yield awesome results. You can do the cool look and mount the antenna on the front bumper as long as it’s metal. Spare tire carriers are a good spot as well. Roof tops are generally regarded as the best, but with non-metallic roofs (Wrangler) that’s just not an option and you also end up with an antenna hitting everything. Find the best metallic place you can mount your antenna and go from there.
Speaking of metallic mounting points; although antennas can operate from mounting points that are not metallic, it really reduces their operating efficiency. The base of the antenna wants to see a ground plane. This ground plane helps conduct the radio wave beyond the antenna. They are normally ¼ wavelength in size which illustrates why this can be a bit of an issue. Ground planes must be conductive like steel, aluminum or even copper. Because of the small nature of VHF and UHF antennas, this is easier to find on a vehicle than the nearly 108 inches needed for the CB antennas. As previously stated, since mounting on a vehicle is never optimal, use what you have available.
Once you have your radio installed, coax ran, and antenna attached you will need to check to see if you are transmitting properly. The instrument needed here is a Standing Wave Ratio (SWR) meter. These are not terribly expensive and often times you may just have a friend who already has one. Leaving all the technical stuff to the side, the SWR meter will let you know how well your setup is operating.
The meters normally have a reading on the left side of 1:1 and 3:1 or higher on the right. You want your reading to be less than 2:1 on the primary channels or frequencies that you operate on. Don’t worry if your reading is 1:5 or similar. Those reading are perfectly fine and will change anyway while you are driving down the road or trail and your antenna is whipping around.
If your SWR meter is showing higher than 2:1, you will need to figure out if your antenna is too long or too short. For instance, if you are attempting to tune your 10* inch CB antenna, start with whatever channel you want to primarily operate on. For this example, we will do Ch. 20. Attach your meter with a small jumper of coax between your radio and the radio end of the coax. Key the microphone. Note your reading. It’s its 2:1, you can leave it or do some investigation. Go down to Ch. 1. If your reading has decreased to 1:1, then what your radio is seeing is a longer than needed antenna on Ch. 20. If the meter indicates a higher SWR, then your antenna is shorter than needed. It’s a confusing subject that takes time to get right. Many antennas have a built in tuning section at the top that you adjust a small amount up or down depending on your goal.
CB radios tend to be more susceptible to SWR problems with length than VHF and UHF. Matter of fact, many VHF/UHF antennas can be operated out of the package without adjustment.