Chirp measurements have been conducted on the pulsed output of an unstable resonator oscillating on the P20 line of the 10.6 micron band of an e-beam sustained CO2 gain medium. A heterodyne method was used, mixing the oscillator signal with a cw laser operating on the same line. The mode volume was approximately 5 liters at a pressure between 1/3 and 1/2 atm. The measurements were conducted at pulse lengths of the order of 20 microseconds and are useful in characterizing the device for use in radar applications. Chirp values of less than 1 MHz are observed during the first 10 μ sec, in the remainder of the pulse, values of several MHz are observed, with decreasing frequency.