Which statement about the relationship between duty factor and depth is correct?

Which statement about the relationship between duty factor and depth is correct?

• A. Duty factor increases with greater depth
• B. Duty factor remains constant with depth
• C. Duty factor decreases with greater depth
• D. Duty factor is unrelated to depth

Answer: (C)

Duty factor is the fraction of time the system spends transmitting versus the total cycle time. It depends on the pulse duration and the pulse repetition period (PRP). The PRP is set by how long echoes from the deepest target take to return, so deeper imaging means a longer PRP. Since the pulse duration stays essentially the same, a longer PRP makes the duty factor smaller. So deeper depth reduces the duty factor. At shallow depths, echoes return quickly, PRP is shorter, and the duty factor is higher. The idea that duty factor stays the same, increases with depth, or is unrelated doesn’t fit with how PRP expands as depth increases.

Duty factor is the fraction of time the system spends transmitting versus the total cycle time. It depends on the pulse duration and the pulse repetition period (PRP). The PRP is set by how long echoes from the deepest target take to return, so deeper imaging means a longer PRP. Since the pulse duration stays essentially the same, a longer PRP makes the duty factor smaller. So deeper depth reduces the duty factor. At shallow depths, echoes return quickly, PRP is shorter, and the duty factor is higher. The idea that duty factor stays the same, increases with depth, or is unrelated doesn’t fit with how PRP expands as depth increases.