Ambient RF field strength measuring and reporting

Company: True North Management Services LLC RFI Measurement Requirements Purpose To measure the ambient RF field strength and its direction of arrival over 360 degrees of azimuth in the band 19.3-20.2GHz where the antennas will operate. Measurement requirements Use a directional, calibrated antenna with low noise amplifier to measure the signal power of each signal. From the known gain of the antenna, LNA and cables, express each measurement as a signal strength in dBW/M2 Mount the antenna at least 3m above the ground, with its boresight aligned horizontally towards the horizon. Rotate the antenna in azimuth with steps no greater than the 3dB beam-width of the antenna. At each azimuth step, make the following measurements and record them; • the azimuth angle • the time of day (UTC or local) • using a spectrum analyzer: o measure the power using an RMS detector, bandwidth and center frequency of each signal that exceeds the measurement system noise floor by >3dB threshold. o Select the frequency span, resolution bandwidth, video bandwidth/filtering and sweep time to obtain a measurement sensitivity goal of -166dBm/Hz (e.g 3dB signal detectable above a noise floor with 6dB NF, referenced to antenna input) o Sweep the complete 900MHz band in segments and record the power vs frequency outputs. • Post processing: o Filter and discard power measurements that are below the 3dB threshold. o Remove the spatial ambiguity caused by the antenna pattern (the same signal appears on main lobe and side-lobes) to identify the true azimuth angle of arrival. o Tabulate frequency, bandwidth and power of each signal detected as a function of azimuth. • Report o Identify the frequency, bandwidth and field strength of those signals that are above the noise floor threshold and include their azimuth angle. Equipment and Measurement notes. a. A 1.2m antenna with LNA is OK. Antenna and LNA gain and noise figure should be calculated or measured to +/-2dB. The test antenna need to be high enough 10ft to give Fresnel zone clearance b. A camera, if it can record azimuth, and time of day is OK. c. The proposed spectrum analyzer settings will need to be checked after connecting to the LNA to get the measurement sensitivity. A note on precautions 1. Avoid azimuth increments that are much larger than the antenna beam-width because signals be missed (spatially) 2. Avoid large bandwidths, fast swept times because the measurement sensitivity will be poor and only very strong signal will be detected. 3. Fast broad sweeps can be initially used to identify high power interference as a first step