K40

K40 Antennas & Accessories FAQ

For answers to some of your most commonly asked questions regarding K40 products, please refer to the infomation below. If your question is not answered in this section, or you require further explanation, please contact K40 customer service department by calling 1-800-228-1291

How important is having a good SWR measurement?

SWR, or VSWR as it's sometimes referred to, stands for Standing Wave Ratio. SWR is an important measurement because it shows how well your CB system, including antenna, coax, mount, and ground plane, matches the output of your CB radio. A perfect match, where all the RF energy the radio is producing is transferred from the radio through the antenna, is considered a 1:1 match.
A high SWR reading (higher than 2:1) is a sign of reflected power (RF energy) going back to the radio. This means some of the power that is transmitting does not make it to the antenna. Besides signal loss, having a high SWR might also result in damage to the radio.
Keep in mind, while a high SWR reading is an indicator of a match problem, a good reading does not necessarily mean your antenna is radiating properly. An example of this is a dummy load. While a dummy load is able to achieve a perfect SWR it does not radiate a signal.
"No Ground Plane" antennas are also an example of this. These specialty antennas are designed to produce low SWR readings in tough grounding situations. Though their SWR match is good, their radiating pattern is very poor for mobile use. Instead of radiating towards the horizon, they tend to radiate skyward, thus limiting the distance you can transmit and receive with them.

What are some common reasons for high SWR?

Insufficient ground plane
Coax problems - Improper type, incorrect length, low quality, or damage
Poor installation location
Antenna not tuned properly to the vehicle
Damage to the antenna

How do I adjust the SWR on my K40 antenna?

Adjusting the SWR for an antenna is usually not that difficult. If you do find that you are having difficulty tuning a K40 antenna, please contact our customer service department. They will be more than happy to refer you to one of our qualified retailers near your area. When tuning a K40 antenna, it's important to use a SWR meter. To properly tune the antenna, please follow these instructions: 1. Connect SWR meter between antenna and radio 2. Measure SWR of first channel (No. 1) and SWR of last channel (23 or 40) 3. Raise or lower whip so both SWR's are equal. If the SWR for channel 40 is too high, lower the whip. If the SWR for channel 40 is too low, raise whip 4. Adjust in increments of 1/8" Note: Keep doors closed and press transmit button each time you measure SWR. Stay away from buildings or high fences.

How important is it to have the antenna grounded to the vehicle?

Good, consistent CB performance depends on having a properly tuned antenna that's been grounded appropriately. An antenna that is not grounded properly is almost assured of having high SWR problems across every channel.

How important is the coax I'm using?

This is an area that many people try to save money on. Don't do it. For single mounted antennas, K40 recommends buying the best quality RG-58 A/U type coaxial cable you can find. For dual co-phased antennas use RG-59 A/U coaxial cable. Be especially careful if you are using factory pre-wired cable in your truck. Historically, manufacturers of these trucks try to use the least expensive cable they can find and rarely does it measure recommended lengths. As you might guess, this leads to tuning problems and inconsistencies in performance.

What length of Coax should I use?

The recommended length for coax is 18 feet. If you cannot use 18 feet, you can use a minimum of 9 feet with increments of 3 feet (example: 9, 12, 15, 18). Please be extremely careful of what you do with your excess cable. If you need to wrap it, let it hang loose and carefully wrap it in a 12 to 16 inch circle (elbow to hand roll), wire tire it in the center, and put it out of sight under your seat or dash. Failure to do so could result in a RF choke.

Can I purchase antennas that are pre-tuned?

Any antenna can be pre-tuned on a test bench, however, once the mounting location is changed to a vehicle, variables such as ground plane and surroundings may affect the antenna. For this reason, "pre-tuned" antennas tend to only work on a small percentage of vehicles. To properly install an antenna you should take an SWR reading every time you move it, even if it's only to another vehicle.

Is power handling important when it comes to choosing an antenna?

The Power handling capability of an antenna should be taken into account as an indicator of the overall quality and durability of an antenna.

I want to use a Whip antenna with a shorter mast for clearance reasons. What performance differences can I expect from using a shorter whip antenna?

The main drawback to using an antenna with a shorter whip is that there is less area to capture and radiate a signal. As a result, the maximum distance for transmitting and receiving a signal is compromised. While the ideal length of an antenna would be 102", for most, driving around town with that long of an antenna is asking for problems. For this reason, antenna manufacturers have specially engineered their antennas by winding the coils in a way that electrically creates that 102" radiating element (whip), without the inconvenience of an 8 1/2'' whip. Most traditional CB antennas today have a minimum total length of 2' and a maximum of no more then 5' or 6'. As a rule of thumb, the longer the whip of the antenna the better it will perform, with obvious differences in the various makes and styles of antennas.

How far can I expect to receive and transmit with a K40 antenna?

Determining range for any mobile CB antenna is impossible because the obtainable distance you can receive and transmit with is influenced by many outside variables. For instance, the style of antenna you are using, the time of day (day or night), atmospheric conditions, type of vehicle the antenna is mounted on, position of the antenna, and the terrain of the surrounding area. This is a big reason why many CB users will experience performance changes with their system from one day to the next. With this in mind, K40 CB antennas are designed to maximize your communication distance, so no matter what the conditions, you can talk farther and receive clearer than ever before.

Is it better to invest more in my CB radio or antenna to achieve the best performance?

Both are equally important components. A good radio, no matter how much you spend on it, will only be as good as the antenna you use with it. If your antenna is not efficiently radiating the RF energy needed to transmit and receive, you will never achieve the maximum performance your radio was designed for. The opposite of this is also true. If you invest everything into the antenna, but your CB radio is not doing its job properly, you won't be happy with the results either. An efficient system, where maximum power transfers from radio through the antenna, requires making a sound investment in both pieces of equipment.