Abstract: Design methodology of high efficiency PCM telemetry transmitter is presented. Practical S band transmis sion line inverse class E power amplifier with series tunable parallel resonant tank using GaN transistor is built. The amplifier circuit is shown to be able to give 10W output power with drain efficiency of 78%. By using this high efficient technique,the telemetry transmitter,which is suitable for 2Mbps PCM signals, obtains an output power 9. 8W with efficiency of 57. 6%.