The communication system of the Iowa satellite ISAT-1 provides contact links between the satellite, the ground station, and a moderate number of remote ground data collection systems through the operation of two functional units. In this system, data is transferred over four VHF/UHF channels, each with a bandwidth of 15 KHz, at the rate of 9,600 bps per channel. The continuous phase binary frequency shift keying (CP-BFSK) is used for digital modulation/demodulation in the attempt to achieve a transmission error bit rate of 10(-6) or lower under the constraint of a very limited financial and power budget. Also, a command-driven time division multiple access (CD-TDMA) scheme is employed for data exchange between the remote data collection systems and the central ground station in order that the communication resources be utilized efficiently and effectively. In this paper, different aspects of the system, including the specifications and the preliminary designs of all operation blocks, are described in detail.