Novel about signals from aliens that turns out to be from dolphins

Question

I read this sci-fI novel as a youngster. The story concerned a signal being detected, presumably from outer-space - from a race of intelligent aliens.

The main human protagonist - a young man, or older boy (if I recall correctly) - sets about to develop a better way to communicate with the aliens. And, having done so, a conversation develops. The aliens wish to interact with humans, sharing knowledge, but are fearful of what humans might do.

It turns out that the signals are actually coming from Earth, from dolphins!

Answer 1

This describes Stationary Orbit by Peter Macey, published in 1974.

A young radio astronomer is working on a new receiver when he picks up signals thought to be from aliens. At the end of the book he finds that a broken cable is actually picking up the brainwaves of dolphins in the local zoo.