Site Equipment Characterization Measurements
A Philosophy that has been followed for the last few years, is to measure emission frequencies, and levels, of all new equipment that arrives on-site, particularly, PCs, test equipment, network related hardware, such as hubs, switches, media converters etc, and any other device which may cause potential interference. These frequencies and levels are measured using the observatory's small anechoic chamber, a facility established in recent years, to measure emission levels using a variety of calibrated antennas, and low noise amplifiers, in combination with a spectrum analyzer. The anechoic chamber provides an environment whereby equipment can emit their RFI, without affecting observatory operations, whilst detailed measurements are made pertaining to that RFI. Frequencies associated with dominant emission levels are recorded, for the main observing bands at the observatory where RFI is of concern for spectral line, and continuum observations, notably 650-750MHz, 1370-1440MHz, and 1600-1700MHz. The noted frequencies are then used to compare to any RFI associated with any spectral line, and continuum observations, that may be reported at later dates. In order to gain an appreciation of what actually constitutes an interferer, particularly to the Parkes Multibeam Receiver, used for HIPASS/ZOA observations, a series of experiments were conducted, whereby, a test transmitter was established, in various localities around the observatory, and used to generate a calibrated RFI signal, into the Multibeam receiver system. The test transmitter level was adjusted, such that a known interference level, as measured through the receiver system, as a % of the system noise, was detected. The transmitter levels were then used to calibrate the RFI emission measurement equipment, used in the anechoic chamber, to give a cross reference between equipment tested, and expected levels of interference on the observatory, at L-Band. This exercise has been of benefit, in gaining some confidence as to what actually constitutues an interferer, and helps to identify which items of equipment may need to be screened, in a purpose built, or commercial screened cage.