A few possible reasons may prevent CBS to come in clear on your TV. For example, the problem could lie with where your TV antenna is positioned or the type of TV antenna you're using.
Try moving your indoor TV antenna closer to a window and turning it to face different directions. Also, try raising your TV antenna above reflective surfaces, such as a mirror, large metallic objects (like a refrigerator) and other appliances, and turn the antenna to face different directions. If raising the antenna above reflective surfaces helps clear up the problem, you're experiencing "multipath interference," which is when a single TV signal reaches your antenna, at slightly different times, via multiple paths, causing interference.
The type of TV antenna you use matters. If you're having difficulty picking up a strong TV signal from your local CBS station, even after adjusting the antenna, you may also need to invest in a roof-mounted outdoor TV antenna. In many instances, however, all you need is a better-quality indoor TV antenna. Your best bet is to use a high-quality multidirectional indoor TV antenna, unless you're having problems with multipath interference. If multipath interference seems to be the reason why CBS won't come in clearly, using a directional antenna will help minimize this problem.
The AntennaWeb and TVFool online tools (see Resources) can help you determine where your local CBS TV broadcast tower is located. You can use this information to not only help you choose the best antenna type but also how to set it.