The propagation of electromagnetic radiation from 500 to 4200 Mc in a coaxial cage transmission line passing through a cylindrical discharge chamber is investigated experimentally. Measurements were conducted in argon, helium, and nitrogen gas at pressures between 0.09 mm Hg and 2 mm Hg for a discharge-electromagnetic radiation interaction length of 30.48 cm. The results are compared with theory using a Lorentzian model to describe the electron motion in the presence of the RF field. A graphical method for determining the plasma frequency and electron momentum transfer collision frequency from measurements of the power transmission coefficient at two different radio frequencies is discussed. A comparison is made between the plasma frequency determined by this method and that obtained by the use of a cylindrical Langmuir probe. The electron momentum transfer collision probability is calculated from the RF and probe data.