Double detuned loop frequency discriminator circuit

The actual circuit of the double detuned loop frequency discriminator used in the microwave communication machine is as shown in the figure. The resonant frequencies of the two loops are set to
35MHz and 40MHz respectively.
    The transistor is 3DG12 and the diode is 2AP9×2.
    In the figure, the FM signal carrier frequency is 37. 5MHz, which is amplified by two common-base amplifiers and then added to two resonant loops respectively, and the connection point of the two
loops is grounded together with the detection capacitor. Since the ground point changes, the output voltage ‰ is taken out from the middle of the detector resistor, so
the directions of the detector diodes VD1 and VD2 are opposite.