Robert Wilson and Arno Penzias weren't specifically trying to discover cosmic background radiation. They were using a large horn antenna, originally built for Bell Labs to communicate with the Echo satellite.

Here's a breakdown:

* Horn antenna: This was the primary tool. It was a large, 20-foot diameter horn antenna designed for communication with satellites. Its sensitivity allowed them to detect faint radio signals coming from all directions.

* Radiometer: They used a highly sensitive radiometer connected to the antenna. This device measured the intensity of radio waves coming from the sky.

* Calibration: They carefully calibrated their equipment to eliminate any potential sources of noise from the antenna itself or other known sources.

* Sky observations: They observed the sky at different times and directions to rule out any possible sources of the persistent background noise.

Their discovery was unintentional - they stumbled upon the cosmic background radiation while trying to eliminate noise in their antenna. This "noise" turned out to be the faint afterglow of the Big Bang, a groundbreaking discovery that revolutionized our understanding of the universe.