Standards for Equipment to Be Deployed on the MRO

RFI Standards for Equipment to be Deployed on the MRO

13 February 2009 (v0.5) Date version Autho comments r 3/8/08 V0 mcs First ideas from meeting 5/8/08 V0.1 rb Added detail 12/8/08 V0.2 cdw Introduction, formality, 15/8/08 V0.3 mcs Minor changes 18/8/08 V0.4 ddb Minor changes in on-going compliance 13/2/09 V0.5 cdw Clarifications – added Annex 1 RFI Standards for Equipment to be Deployed on the MRO

Any electrical or electronic equipment in the vicinity of the Murchison Radioastronomy Observatory (MRO) has the potential to create harmful Radio Frequency Interference (RFI) which could contaminate the radioastronomy observations. This applies to equipment used by the observatory operations as well as that used by external parties. RFI from other users (telecommunications carrier, mining operations, tourists) is addressed in other documentation. This document set limits on the equipment to be deployed on the MRO site itself. Measurement of very low levels which are nevertheless harmful to radioastronomy is difficult. The Military Standard MIL-STD- 461F (RE102 “Navy Mobile and Army” curve) is used as the basis of assessment, as shown in the Table 1 below. For equipment within 10 km of the MRO facilities, control of RFI requires the use of additional screening. This document sets limits on the interference between one experiment and another (for example, ASKAP interference to MWA and vice versa). It is not intended to define limits for interference within a single experiment.

Table 1 Fundamental thresholds for emissions as a function of frequency

Distance Threshold emissions allowable for Comments (km) equipment to be deployed d>10 <= levels defined in Military standard MIL-STD-461F category RE102, Navy Mobile and Army (Figure RE102-4) 10>d>1 <=Military standard MIL-STD-461F Need to take great care with as above, plus a screened box at equipment connections to >20dB maintain RFI screening between tested components d<1 <=Military standard MIL-STD-461F Only permitted on a case-by- as above, plus a screened box at > case basis with careful testing 80dB

The distance (km) refers to the minimum separation between the position of the proposed equipment at the MRO and the nearest facility of another experiment on the site. Annex 1 gives the derivation of these shielding levels and distances to assist in evaluating equipment on a case-by-case basis. A facility may include a single antenna system, multi-element array or any other electrical/electronic equipment(s). Acceptance protocol for equipment on the site. Proponents will be required to have entire systems or subsystems tested in a qualified EMC lab and results assessed by the CSIRO as MRO Management to ensure that equipment meets the standards in Table 1, appropriate to the equipment site on the MRO. A subsystem shall, as practically as possible, replicate the situation that will be deployed in the field. The subsystem should be connected with typical input or output signal lines and typical terminations on those lines. The subsystem should be as large a functional block as practically possible, operating in an active mode and with typical power consumption and loads. Where several functional modes are possible, a representative set of measurements for each operational mode should be made and assessed individually, and the equipment will be required to pass the criteria in each mode. Procedure for approval Before formal testing is undertaken, consultation with the MRO Management will be required to reach agreement on the level of subsystem to be tested and the specific test requirements for any particular instrument, thus minimising the need for retesting. The MRO Management require that EMC laboratory reports, certificates obtained, and plots of equipment test results be prepared and presented to the MRO management to enable characterisation and assessment of the proposed equipment to be deployed on the MRO. CSIRO is investigating options to develop test laboratories in Australia to enable equipment to be tested and characterised prior to deployment. In the meantime, other test facilities which are certified to test to to MIL-STD-461F must be used. Test certificates must be supplied before installation of equipment commences, and all parties are advised to wait for MRO approval before further equipment acquisition. MRO Management will advise within 15 working days if the equipment has been satisfactorily tested and meets the requirements shown in Table 1. CSIRO reserves the right to require equipment to be checked for compliance to MIL- STD-461F and additional screening after commissioning on the MRO site. Testing of screened enclosures From Table 1, screened enclosures are required for equipment within 10 km of another experiment. These should be tested separately from the equipment to be screened, by placing a known source inside the screened enclosure and measuring the attenuation of the signal. As shown in the analysis in Annex 1, the enclosure should meet the specified level of screening (20 dB or 80 dB) over at least the frequency range from 400 MHz to 5 GHz. IEEE standard 299-2006 on measuring screened rooms may be used for measuring screened enclosures greater than 2 m in each dimension. Procedures for measuring smaller screened enclosures are being investigated. In the interim, the use of commercially available screened enclosures is recommended. Ongoing compliance If, in the future, any equipment is found to exceed the threshold limits in Table 1, then the owners and users of the equipment may be required to immediately switch off the equipment so that it ceases to emit RFI. The equipment may need to be either modified so that its levels of emission are within the thresholds defined, or removed from the site. Furthermore, if, in the future, any equipment is found to compromise research activities at higher sensitivities than that specified in the table, over the same receiving bands or in different receiving bands, it will be the responsibility of the owner of the equipment to further minimise or mitigate emission levels affecting other research programs. Reference: MIL-STD-461F: Requirements for the control of Electromagnetic Interference Characteristics of Subsystems and Equipment. http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=35789 Annex 1

Derivation of 20 and 80 dB shielding requirements

The threshold for RALI MS 32 is used as a standard for the level of permissible RFI. The MIL-STD-461F levels for the same frequency breakpoints are derived and converted to dBm/Hz. The difference between the two levels represents the loss which must be achieved either through separation (free-space loss) or additional shielding. A value of 20 dB additional shielding results in separation distances of less than 1 km for most frequency points, while a value of 80 dB shielding brings the required separation down to a few metres. The antenna RFP for ASKAP also specified MIL-STD-461F plus 80 dB.

Shielding RALI threshold MIL-STD-461F 20 dB 80 dB Measurement loss Freq PSD Limit distance Bandwidth PSD needed Distance needed (MHz) (dBm/Hz) dBV/m m kHz (dBm/Hz) dB km m 100 -214 24 1.0 100 -131 83 0.3 0 230 -214 31 1.0 100 -124 90 0.3 0 400 -222 36 1.0 100 -119 103 0.9 1 520 -224 38 1.0 100 -117 107 1.1 1 820 -224 42 1.0 100 -113 111 1.1 1 1000 -228 44 1.0 100 -111 117 1.7 2 2300 -230 51 1.0 1000 -114 116 0.7 1 6000 -232 59 1.0 1000 -105 127 0.9 1 10000 -232 64 1.0 1000 -101 131 0.9 1 25250 -236 69 1.0 1000 -96 140 1.0 1