In general, LEO satellite uses S-band communication link for the whole satellite management, whereas the satellite payload frequently implements X-band and/or Ku-band transmitter for payload data transmission. The transmission system should have out-band rejection filter (protection circuit) to prevent any interference with the satellite receiver, so that the receiver can be normally operated. It is usually implemented in the transmitter itself but the vendor of a transmitter could not take it into account whole out of band frequency because a variety of individual satellites utilize different RF communication systems. The KOMPSAT-II, which is an earth observation satellite, is being developed by Korea Aerospace Research Institute and Korean industries. It has S-band communication system for the bus and X-band transmission system for payload data. In addition, L-band GPS Receiver is being incorporated to achieve the KOMPSAT-II mission goal. Unfortunately, the KOMPSAT-2 payload system does not have external out-band rejection~ filter nor transmitter for S-band and L-band protection. The transmitter only has band rejection filter for TDRSS. In addition, it has high gain directional antenna whose directional beam has to pass over the S-band antenna. In this paper, the analysis method is described to calculate the interference effects of the S-band spurious noise power on X-band transmitting system to S-band receiver. The S-band antenna is positioned very closely to the X-band Antenna by I .2m. We will also introduce general simple RF interference analysis method applicable to a traditional system, including advantage and disadvantages. The X-band transmitting system is often required to add the specified filter to suppress the S-band spurious signal for the safety of the receiver performance. The analysis result shows that the performance of S-band receiver is satisfied with no implementation of the specified filter.