# How to read hydrophone plots

RESON calibrations use pulse-gated measurement techniques are used to avoid reflections in the tank. Voltage, current, and impedance are all measured within the same gated pulse. The pulse width is limited by its wavelength and the size of the tank. Due to the size of our tank, we only calibrate down to 5kHz. We also perform a pistonphone calibration test at 250Hz.

### HOW TO READ THE PLOTS - Physical Orientation

When we calibrate our hydrophones, they are lowered into the tank vertically, tip first into the water.

### HORIZONTAL DIRECTIVITY

Orientation in the tank is vertical in the water, perpendicular to the direction of the source signals coming from the reference projector. To read the plot, think of Hydrophone tip going into the center paper plot. 0-degree is at the S/N. Horizontal Directivity measurements are taken at a single frequency, and the Hydrophone rotates on axis from 0-deg to 360-deg.

### VERTICAL DIRECTIVITY

Orientation in tank is sideways, parallel to water's surface, in same axis as the direction of the source signals from the reference projector. To read the plot, think of laying the hydrophone on top of the paper plot. 0-degree is the tip, 180-degree is the cable end. Vertical Directivity measurements are taken at a single frequency, and the Hydrophone rotates on the same plane from 0-deg to 360-deg.

### RECIEVE (and TRANSMIT) SENSITIVITY Plots

The receive and transmit frequency sweeps are taken at a single point on the hydrophone, at the 0-deg in the Horizontal plane. In other words, the source projector directs signals at the side of the hydrophone, at the physical location where the S/N is inscribed (0-deg in the Horizontal plane)

### IMPEDANCE PLOTS

During the impedance measurement we run the hydrophone as a transmitter (drive it with an amplifier capable of providing the current needed) and measure the voltage, the current and the phase between voltage and current. Based on this we get the impedance. U=Z*I. All complex numbers (magnitude and phase) I=Im(cos(phi)+j•sin(phi)) = Im•e^(j•phi), (by Euler’s theorem). Electronic engineers will call this a Phasor representation. The impedance Z = U/I, it will be a complex number where R is the real part and X is the imaginary part and Zm is the size or the magnitude (modulus) Zm=(R^2+X^2)^0.5.