Nano satellites are generally developed by universities for scientific researches because of low design cost and time. On the other hand a nano satellite has small power and limited volume; therefore there are several restrictions for circuit design. In this project, a digitally controlled VHF to UHF analog transponder is presented for nano satellites. System has -115 dBm receive sensitivity. Output power is 1W at 437.225 MHz with +/-35 kHz narrow bandwidth. Transponder is controlled by a microcontroller to keep output power stable as 30 dBm (1W) with +/-1.5dB ripple. Circuit size is 9x9 cm(2) and includes a metal shield. System was tested under space conditions such as vacuum and very high temperature changes. System is pin to pin compatible with other commercial nano satellite devices' bus structures.