High frequency discriminator with a crystal phase shift network

For use in developing an audio voltage in a receiver for angle modulated waves, said receiver including signal developing means for developing a signal voltage in the frequency range of at least several Mhz which is deviated about a center frequency by a deviation of several Khz in accordance with the modulation of the modulated wave;

• a discriminator circuit of the type adapted to combine the signal voltage and a quadrature voltage and having an input adapted to be coupled with said signal developing means, a crystal phase shift network in the discriminator circuit including a piezoelectric crystal and additional reactance means including distributed capacitance, said crystal with the additional reactance means having a reactance which is linearly proportional to signal deviation from center frequency, said phase shift network also including, in series with said crystal, a series impedance comprising reactance which includes distributed capacitance, the series impedance being resistance, said crystal being resonant at a frequency within a few Khz of said center frequency, whereby a modified signal voltage is produced across said series impedance, said modified signal voltage having a phase shift relative to said signal voltage which is linearly proportional to the deviation of said signal voltage frequency from said center frequency and means coupled with the crystal phase shift network for shifting the phase of the modified signal voltage by an additional 90.degree. to produce said quadrature voltage, whereby said quadrature voltage is in quadrature phase relation with said signal voltage when the signal voltage is at said center frequency.