International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper introduces two transponders combining coherent transponding and non-coherent transponding for multistatic trajectory measurement system and carrier Doppler frequency extraction principle, then derives each model of the velocity error for noise. The expressions of velocity error resulted by noise in coherent, IF-modulated and IF transform transponding configurations are also described. The conclusion is drawn: the system velocity error for noise is related to the transponder transponding configuration. And, the velocity error in coherent, IF-modulated and IF transform transponding configurations are compared in this paper.