What type of GPS can pick up both L1 and L2 signals?

The answer is correct because dual frequency GPS systems are designed to receive signals from two different frequency bands: L1 and L2. The L1 frequency operates at 1575.42 MHz and is primarily used for civilian GPS signals, while L2, at 1227.60 MHz, is primarily used for military applications but also provides additional signals for civilian use. By utilizing both frequencies, dual frequency GPS receivers can significantly improve accuracy and reduce errors caused by atmospheric conditions, such as ionospheric delay. This capability enhances the overall performance of GPS navigation, making dual frequency receivers preferred for applications requiring high precision.

In contrast, single frequency GPS systems only operate on L1, limiting their precision and susceptibility to atmospheric interference. Twin frequency refers to systems that can handle two signals but may not specifically mention both L1 and L2. Extended frequency typically refers to advancements beyond standard frequencies and does not specifically signify the capability to receive both L1 and L2. Thus, dual frequency is the most precise and effective answer regarding the ability to pick up both signals.