Before revision: A transponder is typically composed of: an input band-limiting device (an input band-pass filter), an input low-noise amplifier (LNA), designed to amplify the signals received from the Earth station (normally very weak, because of the large distances involved) a frequency translator (normally composed of an oscillator and a frequency mixer) used to convert the frequency of the received signal to the frequency required for the transmitted signal, an output band-pass filter, a power amplifier (this can be a traveling-wave tube or a solid-state amplifier).
After revision: ,A transponder is typically composed of: an input band-limiting device (an input band-pass filter), an input low-noise amplifier (LNA), designed to amplify the signals received from the Earth station (normally very weak, because of the large distances involved) a frequency translator (normally composed of an oscillator and a frequency mixer) used to convert the frequency of the received signal to the frequency required for the transmitted signal, an output band-pass filter, a power amplifier (this can be a traveling-wave tube or a solid-state amplifier).