This paper describes the design and evaluation of new GNSS jamming detection methods for position, navigation and timing (PNT) situational awareness (SA). These methods are intended for implementation over large networks of GNSS receivers. We focus on jamming threats caused by personal privacy devices (PPDs). We first derive two new jamming detection tests to identify events of simultaneous drops in C/N0 impacting all satellites in view. To limit the risk of false alerts, we develop an automated process to model satellite-specific and receiver-station-specific C/N0 measurement variations under jamming-free conditions. These models are then incorporated in our new detectors and evaluated using months of GPS L1 C/N0 data from continuously operating reference stations (CORS). Tens to hundreds of events are detected monthly at CORS sites located next to highways. To confirm that the detected events are caused by jamming, we analyze CORS data over multiple days at multiple locations, and find patterns in jamming schedules. In addition, we process ADS-B-reported aircraft receiver data during two known radio-frequency interference (RFI) events that also impacted CORS data.