Abstract: An FM stereo generator for use as a modulator or in a test instrument or the like to provide the conventional 19 KHz and 38 KHz signals. The phase of the generated 19 KHz pilot subcarrier signal is fixed relative to the 38 KHz carrier signal. The 38 KHz double sideband suppressed carrier signal is generated in a digital synthesis circuit to provide a stable 38 KHz carrier signal. The left and right stereophonic audio signals are applied to operational amplifiers to provide sum and difference audio components. The difference component is applied as an input to a double sideband suppressed carrier digital-to-analog converter which is responsive to the synthesis circuit to provide the 38 KHZ carrier signal. The 19 KHz pilot subcarrier signal is generated by a digital-to-analog converter that is clocked by a crystal timer which is common to both signals thereby to lock the phase of the pilot signal to the 38 KHz signal.

Abstract: An RF carrier applied to the antenna input of a radio receiver under test is sequentially modulated with an audio signal to provide sequentially at the audio output of the receiver a signal plus noise signal and a noise signal, which audio output signals are compared to provide a ratio voltage which is displayed to permit adjustment of the level of the RF carrier to set said ratio at a predetermined value.