Abstract
AbstractThe present note describes a modulation recorder for amplitude modulated signals that can automatically record by means of a pen and ink recorder the received percentage modulation of a fading sky-wave signal. The equipment employs the principle that if the ratio of the sideband amplitude to the carrier amplitude were determined, the percentage modulation can be known. The rectified D.C. voltage corresponding to the carrier and the audio voltage corresponding to the sidebands are separately obtained from the second detector of a Hammarlund “super-pro” receiver. The D.C. value corresponding to the audio voltage is obtained in a crystal rectifier. Logarithms of the D.C. voltages, corresponding to the carrier and sidebands are derived in a twin channel log-amplifier and the outputs of the two channels are fed into a subtraction unit consisting of a push-pull double triode. The output of the subtraction unit is a direct measure of the received percentage modulation and is recorded by a pen and ink typ...
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