I have fitted an Airmar P79 sonar to my Raymarine A77, works well except that when I switch to Charts or any other page except Sonar I hear a 240 beats per minute ticking. These units produce 200kHz ie 10 times higher than human hearing so it is not the transducers themselves. The hull is solid fibreglass and mounted according to manufacturer's specs.
Why tick only when not on the Sonar page? Miss Google has many pages devoted to the topic but none have addressed the specific Sonar page. As always I welcome your opinions.
Don't know the answer to your specific issue with the Airmar P79 sonar and your Raymarine unit. Most likely it is the transducer you are hearing but not the ultrasound, active sonar transducers contain a piston that oscillates within a cylinder to the frequency required. My old Fuso sounder is often noisy for 30 seconds or so when switched on and doesn't give a reading until it warms up. Some high end fisheries transducers I have used can generate enough heat that they can burnt out if operated out of water.
Just guessing now, but perhaps power goes to the transducer all the time but the transmit-receive pulses are regulated differently when the sonar mode is selected?
That's a good point, this is my first experience with sonar and I thought a slow motion cicada had come onboard.
Anyway it still let's me know the depth and bottom condition which is what I got it for.
