Troposcatter carries radio traffic beyond the direct radio horizon by receiving a small portion of energy scattered in the troposphere. It can connect distant ground sites without a relay satellite or an intermediate tower at every horizon. Its usefulness depends on the entire path, antennas, radio equipment and required service availability.
On a narrow screen, swipe tables sideways or focus them and use the arrow keys.
Understand the common scattering volume
Ordinary line-of-sight microwave links are designed around a sufficiently clear path between antennas. On a troposcatter link, directional antennas at the two endpoints point toward a region of the lower atmosphere visible to both antenna beams. Variations in atmospheric refractive index scatter some transmitted energy toward the receiver. The received fraction is small, and the signal varies with time.
- Endpoint A: modem, radio and directional antenna
- Overlapping antenna beams in a common tropospheric volume
- Endpoint B: directional antenna, radio and modem
ITU-R P.617-6 (2025, PDF) provides prediction methods for trans-horizon radio-relay paths. It treats transmission loss statistically, including longer-term variation and rapid fading. A useful design therefore asks what performance is available for a stated fraction of time, under the relevant path and climate assumptions.
Compare paths around the actual service
| Path | Useful circumstances | Questions to resolve |
|---|---|---|
| Line-of-sight microwave | Clear endpoints or feasible relay sites | Terrain profile, clearance, tower needs, frequency coordination and power at each site |
| Troposcatter | Terrestrial endpoints beyond direct visibility | Path geometry, antenna size, power, diversity, fading and availability at the required data rate |
| Satellite | Sites served by an appropriate satellite service | Terminal view of sky, service coverage, capacity, latency, subscription and provider dependencies |
An offshore site is a useful example because the engineering question includes more than distance. How much deck space is available? Can the land station be placed where the path works? What maintenance access is realistic? How should the system behave during reduced capacity? A terrestrial route and a satellite route may also share a local power supply or router, so buying two links does not automatically remove common failures.
Comtech’s troposcatter product family shows that the technology is implemented in multiple equipment forms. A product family establishes available approaches; the exact radio, antenna and path analysis establish the proposed installation.
Separate modem rate, throughput and availability
A headline data rate can describe a modem mode under favorable conditions. Application throughput also depends on framing, error correction, protocol overhead and retransmissions. An adaptive radio may change its modulation or coding as conditions change. Ask for the minimum committed application throughput and the conditions under which it is expected, alongside peak rate.
Explain what diversity contributes
Diversity gives a receiver more than one version of the information, using a documented arrangement such as separated antennas or frequencies. Its value depends on how independently those branches fade. Two branches experiencing the same failure offer little improvement for that event. Antenna placement, frequency use and combining behavior are engineering inputs, not interchangeable accessories.
Comtech’s 2021 family-of-systems white paper (PDF) describes representative systems and diversity configurations. Its distances and rates belong to those configurations and assumptions. Use them to understand a design vocabulary, then request evidence for the proposed path.
Write a useful link brief
- Endpoints: coordinates, elevations, terrain profiles, available antenna locations and access constraints.
- Service: application rates in each direction, latency, packet loss, traffic priorities and growth.
- Availability: the service threshold, annual or worst-month time basis, and acceptable outage duration.
- Equipment: antenna configuration, radio mode, diversity, power, enclosure and monitoring.
- Evidence: propagation model, assumptions, field-test plan and measured acceptance criteria.
Keep path prediction and field acceptance together. A demonstration on another route supports feasibility; a monitored test on the proposed route supplies more relevant evidence. Preserve reduced-rate periods in the logs so that a peak-speed demonstration does not hide service interruptions.