In a synchronous modem, which functional section typically contains the scrambler used to randomize the data stream for clock transparency and spectrum shaping?

Introduction:
Scramblers are applied to digital data streams to break up long runs of identical bits, aiding timing recovery, reducing spectral lines, and improving performance over certain channels. In synchronous modems, scramblers help maintain clock transparency prior to modulation.

Given Data / Assumptions:

• We are discussing internal modem functions, not higher-layer encryption.
• Goal is to condition the bitstream before it drives the modulator.
• Descrambling must occur at the far-end receiver to recover the original data.

Concept / Approach:
The scrambler operates in the transmit path so that the signal entering the modulator has randomized bit patterns. At the receiving modem, a descrambler in the receive path restores the original data. This pair preserves data integrity while improving timing and spectral properties during transmission.

Step-by-Step Solution:
1) Identify where bit preparation is needed → before modulation.2) Place scrambler in the transmission section so the modulator sees randomized bits.3) Complement with a receiver-side descrambler to reconstruct the original stream.

Verification / Alternative check:
Block diagrams of synchronous modems show the scrambler inline with the transmit chain and the descrambler inline with the receive chain, confirming the placement.

Why Other Options Are Wrong:

• Terminal section: refers to the attached DTE, not internal modem conditioning.
• Receiver section: contains the descrambler, not the scrambler.
• Control section: manages settings; it does not process the data stream.
• None of the above: invalid because the transmission section is correct.

Common Pitfalls:
Confusing scrambling (for spectral/randomization purposes) with encryption (for confidentiality). They are conceptually different processes.

Final Answer:
Transmission section contains the scrambler