Status of LWDA Electronics RF Emissions Measurements

This document summarizes recent efforts to characterize the emissions from LWDA electronics still in development. Near final versions of the ARL-developed variable gain stage (otherwise known as the second gain stage or SGS) and digital receiver (RX) have been completed, fabricated and tested recently; a near final version of the adder board is expected in the next few weeks. Individual enclosures for each the SGS, RX, and adder have been designed. To date, the enclosures for the SGS and RX have been fabricated and tested, while a prototype of the adder enclosure (which will accommodate both current and next revision of the adder) is expected within two weeks. It is expected that these individual board enclosures would provide some level of shielding of the emissions from the boards. Development of an intermediate chassis (known as the Level 1 chassis), which would house 8 RX and one adder, is in progress. This chassis is expected to provide an additional layer of shielding of emissions from the electronics boards and cabling between the boards. The completion and fabrication of this design is expected to be well over a month from now. A shielded rack has been purchased from Equipto, and is expected to arrive within two weeks, though the final modifications that must be made to the rack to accommodate LWDA system components will not be made for some time. For the initial LWDA deployment, two Level 1 chassis, a Level 2 chassis containing the final adder, the station computer, and other system equipment will be housed in this rack, which provides additional shielding. This rack will be housed at the LWDA site inside a shielded hut, which is expected to provide a final layer of shielding. Final modifications to the hut are currently in progress and should be completed in roughly 2 weeks. In parallel to the development of the system components that will be deployed at the LWDA site, a shielded NEMA enclosure has been developed to enable near-term field testing of the full LWDA receive chain (antenna to PC). It houses three gain stages, an LWDA receiver and adder, and power conditioning circuitry. It provides two RF coaxial inputs and one USB interface to connect the adder to a PC for control/data download. The enclosure is large enough that a laptop can be placed inside and run off its batteries if there is a concern about its emissions interfering …