Long-distance terrestrial links: Which data transmission medium offers the largest terrestrial range between endpoints without using repeaters or intermediate devices?

Introduction / Context:
Different media support different maximum spans before amplification, regeneration, or relaying is required. For terrestrial (earth-bound) point-to-point links, practical un-repeated distance depends on physics, line-of-sight, attenuation, and atmospheric effects. Selecting the medium impacts deployment cost, availability, and reliability.

Given Data / Assumptions:

• “Terrestrial” excludes space-based relays (i.e., satellites).
• We compare typical un-repeated spans under practical engineering limits.
• Environmental constraints like weather and terrain apply.

Concept / Approach:
Terrestrial microwave links (licensed bands) use high-gain dish antennas and clear line-of-sight paths over towers or hilltops. With proper fade margins and frequency planning, single hops of tens of kilometers are routine, and longer hops are possible under favorable conditions. By contrast, “hardwiring” (copper) suffers higher attenuation and noise pickup over distance without active repeaters. Free-space optical (laser) links can be high-bandwidth but are severely limited by fog, rain, and alignment, reducing dependable reach compared with microwave. Satellite is not terrestrial and relies on off-earth relays, so it does not meet the question’s constraint.

Step-by-Step Solution:

Verification / Alternative check:
Real-world telecom backbones have historically used multi-hop microwave routes with typical hop lengths of 30–50 km (or more with tall towers and high fade margins), validating microwave’s superior un-repeated terrestrial reach relative to copper or free-space optical.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming fiber is implied by “hardwiring” (the option explicitly states hardwiring, i.e., copper). Also, mistaking theoretical optical ranges for practical carrier-grade availability.

Final Answer:
Microwave.