Three teens, two boys and a girl, construct a computerized monitor that as they increase the power, allows them to see farther into the universe and ultimately, another life form in a far galaxy. One kid is the genius, another provides the money. At the end, they conjure images of aliens.
Is it possible that you're slightly misremembering Danny Dunn and the Voice from Space by Raymond Abrashkin and Jay Williams?
Professor Bullfinch has created a radio telescope ("dish") for the government which will try to determine if extraterrestrials are trying to contact Earth. When Danny sneaks into the observatory, he hears non-random sounds coming from space. He then must figure out how to translate the sounds.
It's a radio telescope, not a visual one, but if I recall correctly, they do get a transmitted message that, once they figure out how to decode it, includes an image of a humanoid creature. Danny is often accompanied by his two classmates, Irene and Joe. Dunn is precocious, but not really at a genius level. Professor Bullfinch is the source of the fantastic inventions that drive the plots of the books.
The decoded message
Another possibility is Macroscope, by Piers Anthony first published in 1969. It has a love triangle, a super-genius young person, and a device that can peer across extreme distances to establish contact with intelligences from other worlds.
Its plot synopsis reads -
Macroscope Throughout history, man has been searching for better ways to gather information about his universe. But although they may have longed for it, not even the most brilliant minds could conceive of a device as infinitely powerful or as immeasurably precise as the macroscope, until the twenty-first century. By analyzing information carried on macrons, this unbelievable tool brought the whole universe of wonders to man's doorstep. The macroscope was seen by many as the salvation of the human race. But in the hands of the wrong man, the macroscope could be immensely destructive-infinitely more dangerous than the nuclear bomb. By searching to know too much, man could destroy the very essence of his mind. This is the powerful story of man's struggle with technology, and also the story of his human struggle with himself. This novel takes us across the breathtaking ranges of space as well as through the most touching places in the human heart. It is a story of coming of age, of sacrifice, and of love. It is the story of man's desperate search for a compromise between his mind and his heart, between knowledge and humanity.