The Signal Corps Test Oscillator TS-170/ARN-5 is a piece of electronic equipment used for testing and calibrating radio communication systems. It was developed by the US Army Signal Corps in the 1940s and 1950s and was widely used by the military during that time.The TS-170/ARN-5 operates in the frequency range of 1.5 to 20 MHz and can generate both continuous wave (CW) and modulated signals. It has a built-in power meter, an audio oscillator, and a modulation meter, among other features. The equipment was designed to be portable and rugged, making it suitable for use in field conditions. The TS-170/ARN-5 was widely used by the US military during World War II and the Korean War. It was also used by civilian radio operators and by some foreign militaries.