The FORTE Receiver and Sub-Band Triggering Unit

The FORTE payload receiver and trigger unit represent a significant advance over the currently flying BLACKBEARD payload aboard the ALEXIS satellite. Not only is the polarization sensitive antenna array massive compared to the BLACKBEARD monopole, but the event triggering scheme is completely different. Electromagnetic pulses (EMPs) are dispersed when they pass through the ionosphere creating a chirped frequency signal which can be helpful in discriminating between natural and man-made signals. Payloads designed to digitize and store the RF signatures of these signals must include sophisticated triggering circuitry to select events of interest and prevent false alarms from wasting the available memory storage resources. The FORTE wideband receiver tunes from 20 to 320 MHz with sub-band trigger channels distributed across the 20 MHz IF bandwidth. The conditions which must be satisfied to generate an event trigger are processor controlled. Early testing of the prototype indicates an ability to reliably trigger on chirped RF signals several dB below the noise level. FORTE is scheduled to be launched with a Pegasus XL vehicle in late 1995