August 20, 2020
In response to the FCC announcement of the expanded use of unlicensed equipment into the 6 GHz band, Aviat Networks, along with Ameren (utility operator with large Aviat install base) and EPRI (non-profit research & development organization), agreed to execute a series of field tests to determine potential impact unlicensed equipment could present into an existing microwave radio path.
The field testing would further aid in understanding the behavior of any potential impairments or risks to existing operators in the lower 6 GHz spectrum band. These joint tests follow up initial lab tests conducted by Aviat Networks, in which a radio link was interfered by a commercially available, unlicensed multi-point system that was supporting two clients. In those tests, it was observed that the nature of unlicensed, varying, single shifts in frequency could introduce harmful interference to a fixed, point-to-point microwave system. The interference ranged from moderate to severe, depending on the signal intensity and frequency separation. Based on these findings, a field test was developed to reproduce the effects of the unlicensed signal on a real-world microwave link.
The goal of these tests was to determine the potential impact unlicensed interference could have on the Ameren microwave network. The victim site would have test-points set up near and around the site and transmit an unlicensed signal towards the victim “receive” site and measure the impact observed by the microwave radio using Aviat Networks management tools, including the FAS Expert System. The observed effect would include any interference through the main lobe and would find the edge of the main lobe, side lobes, and back lobes.
The location and path chosen were in the mid-west market at a power plant location that had a path of 29.9 Km (18 mi) with an unobstructed line of site.
The field test was carried out by using a portable interferer and a Vector Signal Generator. The portable interferer was moved and positioned at various points in and around the microwave radio’s path. These points included direct in-path facing the victim site, outside the main path facing the victim site, and directly behind the victim site.