Question
How is an upload signal processed by an inverting linear transponder?
Answer Options
- A) The signal is detected and remodulated on the reverse sideband
- B) The signal is passed through a nonlinear filter
- C) The signal is reduced to I and Q components, and the Q component is filtered out
- D) The signal is mixed with a local oscillator signal and the difference product is transmitted
Correct Answer: D
Explanation
The fundamental function of any transponder is to receive signals at an uplink frequency and retransmit them immediately on a different downlink frequency. In a linear transponder, the relationship between the input and output frequencies must be linear (meaning no distortion of the relative signal spacing), but for an inverting type, the frequency order is reversed.
This frequency reversal is achieved in the mixer stage of the transponder. The process involves mixing the received uplink signal with a stable Local Oscillator (LO) signal. For an inverting transponder, the output signal is created by taking the difference product between the uplink signal and the LO signal, which results in the desired frequency reversal and retransmission.
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