garagedrone @ dronegarageblog.wordpress.com build a 5.8GHz spectrum analyzer using Arduino nano and BOSCAM rx5808 receiver module which is very popular on FPV RX (receiver) builder scene:
At the price of 9 dollars the BOSCAM rx5808 receiver module is very popular in the FPV RX (receiver) builder scene. By default it supports only 8 channels with dip switch. But by using it with SPI interface and Arduino with rx5808-pro open source setup it becomes a comfortable deluxe RX with nice autoscan and a spectrum anlyser.
Arduino and RX5808 module spectrum analyzer – [Link]