A Method of Measurement of Flame Attenuation at 200 Mc

This paper presents a simple method for the determination of the attenuation encountered by a VHF signal as it passes through a flame or the exhaust trail produced by a flame. The measurements are made of the VSWR and the shift of the minimum electric field as the ionized gases pass between two parallel plates of a short-circuited, two-bar transmission line. The relative dielectric constant and the conductivity of an ionized gas are plotted for several electron densities and collision frequencies for a frequency of 200 Mc. Another set of curves is derived from these for attenuation and minimum shift due to ionized gases in a predetermined length of transmission line. Characteristic impedance curves are also plotted. Simple Smith chart techniques are used to determine the VSWR and minimum shift when ionized gases pass through a length of shorted transmission line. The length corresponds to a half wavelength of the wave in the line with no ionized gases present. Calibration was accomplished with the use of distilled water.