*Question G9A06:
In what units is RF feed line loss usually expressed?*  

*Correct Answer is  D: Decibels per 100 feet*  

### AI Response: (may contain errors)  

RF feed line loss is typically expressed in terms of how much signal power is lost as it travels through the feed line. This loss is usually given in decibels (dB) per a specific length of the feed line, which allows for easy comparison and calculation.

1. **Correct Answer: Decibels per 100 feet (Choice D)**  
   - **Explanation**: Decibels (dB) are a logarithmic unit used to express the ratio of power levels. When it comes to feed line loss, expressing it in dB per 100 feet is standard because it provides a clear and manageable way to calculate and compare losses over different lengths of cable. This unit is practical for amateur radio operators who often work with feed lines of varying lengths.

2. **Why the Other Choices are Incorrect**:
   - **Choice A: Ohms per 1,000 feet**  
     - Ohms measure resistance, not power loss. While resistance can contribute to power loss, it is not the standard unit for expressing feed line loss.
   - **Choice B: Decibels per 1,000 feet**  
     - Although decibels are the correct unit, the standard reference length for feed line loss is 100 feet, not 1,000 feet. Using 100 feet allows for more precise calculations over shorter distances, which are common in amateur radio setups.
   - **Choice C: Ohms per 100 feet**  
     - Similar to Choice A, ohms measure resistance, not power loss. Feed line loss is not typically expressed in ohms.

3. **Useful Formula**:
   - To calculate the total loss in dB for a given length of feed line, you can use the formula:  
     $$ \text{Total Loss (dB)} = \text{Loss per 100 feet (dB)} \times \left(\frac{\text{Length of feed line (feet)}}{100}\right) $$  
   - This formula helps you determine the total loss over any length of feed line by scaling the loss per 100 feet to the actual length used.