I am using the following receiver and transmitter for my project to form a ultrasonic communication system. I transmitted 5V Peak to peak voltage, 40 Khz frequency sinusoid from the transmitter and received the signal through the receiver. But the receiver shows the peak-to-peak voltage of about 30V (though I transmitted 5V) when I bring it closer to the transmitter. I was supposed to find out the loss in the received signal and design the Operational amplifier accordingly. But I am stuck due to this amazing amplification in the signal. Please help me out.