"clear line of sight" is correct and can be used in written English.
You can use it to describe a situation where you have an unobstructed view of something, usually at a distance. For example, "The mountaintop provided us with a clear line of sight to the distant valley below."
They like a clear line of sight as much as I do.
All a satellite dish needs is a clear line of sight to an orbiting satellite.
Some Pakistani military positions were less than a mile from insurgent firing positions — and had clear line of sight.
A clear line of sight in a vast landscape goes a long way toward making a person feel small.
The problem is that, until now, most WLL systems were fixed and required a clear line of sight from the customer's building to the service provider's base-station.
As the marines struggled to find a clear line of sight on the men with motorcycles, someone peeled away from the exodus and began walking toward us.
Visual signals are immediately located in well-lit environments with a clear line-of-sight.
Visual signals are designed to be detected against the background in an environment with a clear line-of-sight between communicating individuals.
As a result, there was very little mobility in the channel during each experiment, and each node had a clear line-of-sight to the other two.
As GPS requires clear line-of-sight for accurate services of positioning and localization applications, we designed a Time of Arrival (ToA) based algorithm for areas where strong GPS signals are unavailable.
The Global Positioning System (GPS) is an attractive option for outdoor environments, but is not suitable for indoor applications because it needs a clear line-of-sight to orbital satellites in order to track position.
