A strong digital communication transmitter in close physical proximity to a receiver of a weak signal can noticeably interfere with the latter even when the respective channels are tens or hundreds of megahertz apart. When time domain observations are made in the signal chain of the receiver between the first mixer and the baseband, this interference is likely to appear impulsive. The impulsive nature of this interference provides an opportunity to reduce its power by nonlinear filtering, improving the quality of the receiver channel. This article describes the mitigation, by a particular nonlinear filter, of the impulsive out-of-band (OOB) interference induced in High Speed Downlink Packet Access (HSDPA) by WiFi transmissions, protocols which coexist in many 3G smartphones and mobile hotspots. Our measurements show a decrease in the maximum error-free bit rate of a 1.95 GHz HSDPA receiver caused by the impulsive interference from an OOB 2.4 GHz WiFi transmission, sometimes down to a small fraction of the rate observed in the absence of the interference. We apply a nonlinear SPART filter to recover a noticeable portion of the lost rate and maintain an error-free connection under much higher levels of the WiFi interference than a receiver that does not contain such a filter. These measurements support our wider investigation of OOB interference resulting from digital modulation, which appears impulsive in a receiver, and its mitigation by nonlinear filters.

Measurements of the complex permittivity and permeability of solids at high electromagnetic field greater than 10 kV/m pose a significant challenge to RF connectors and input amplifiers of the measurement equipment. Specifically, difficulties arise in measuring materials with high imaginary permittivity or low impedance, which act as short circuits, either exceeding the measurement equipment damage threshold or that of the material under test, and/or inducing an unacceptable signalto-noise in the collected data. In this work, we report the development of a new measurement technique where we introduce an outer air-gap between the material under test and the conductor of a coax airline. The introduced air-gap reduces the effective conductivity of the sample, mitigating damage to the materials under test and allowing for high power measurement. This study compares the ability of air-gap correction methods to recover the complex permittivity and permeability to within 10% of the value measured without an air-gap introduced.

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