ASLبشمهندس عسل

Mission geometry

Doppler and Propagation Delay Tool

Separate carrier frequency shift from geometric signal flight time.

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Enter the design inputs, then calculate to inspect the results.

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Doppler direction and signal flight timeReceding · Δf = -46698.97 HzGround receiverLower received frequencyRelay pulse · elapsed 0.00 msStation AStation BUplinkDownlinkOne way 238.74 ms · RTT 477.48 ms
Motion is illustrative along the line of sight, not an orbital pass prediction. Positive radial velocity means recession. The pulse spends time on each leg in proportion to its distance; the drawn legs are schematic. Playback expands one computed relay flight to four seconds. No autoplay; use the slider for a motion-free view. Processing and network delays are excluded.

LEO overhead pass

Circular orbit above a fixed station on a non-rotating spherical Earth. This is a teaching model, not a real satellite tracker.

Doppler versus elapsed visible-pass timeDoppler ±44.2 kHz · zero at zenithRise: approachingSet: receding
Time 458.7 / 917.3 s · elevation 90.0° · range 800.0 km

Radial velocity 0.0 m/s · Doppler 0.0 Hz · orbital speed 7455.5 m/s

At zenith radial velocity is zero while orbital speed is not. Uses the carrier frequency and constant mode selected above. Independent pass controls do not replace your entered radial velocity. Earth rotation, inclined/off-centre passes, drag and refraction are excluded.

Understand the system

Signed Doppler shift

A LEO satellite approaching a station raises received carrier frequency; recession lowers it. Use radial velocity along the line of sight, not total orbital speed. Here positive v_r means recession; the first-order approximation applies when speed is much smaller than c.

Δf≈−fcvr/c\Delta f\approx -f_c v_r/c

f_c: Hz; v_r: m/s, positive receding; c: m/s; Δf: Hz.

A faster carrier produces a larger Doppler shift for the same radial speed.

Source: finalExam.pdf · PDF page 1

Common mistakes

  • Convert km/s to m/s when c is m/s.
  • One slant range is not a full ground-to-ground relay path.
  • Do not assume orbital speed equals radial speed.
Formula reference and symbol definitions

First-order Doppler

Δf=−fcvr/c\Delta f=-f_cv_r/c

f_c: Hz; v_r,c: m/s

v_r positive receding; |v_r| much smaller than c.

Example: At 2 GHz and recession velocity +6000 m/s, Δf = −2 × 10⁹ × 6000/(3 × 10⁸) = −40000 Hz.

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Propagation delay

t=d/ct=d/c

d: m; c: m/s; t: s

Geometric flight time only.

Example: A 36000 km path gives t = 36 × 10⁶/(3 × 10⁸) = 0.120 s one way.

Open related tool →

Continue the signal path

Orbit & Kepler Calculator →GEO Look Angle Calculator →

Design guide

Use the result with engineering context

Technical content reviewed

When this tool is useful

  • Calculating radial velocity with engineering models
  • Calculating approach and recession with engineering models
  • Calculating one-way and round-trip delay with engineering models

What the result includes

  • Separate carrier frequency shift from geometric signal flight time.
  • Explanations, assumptions and links to related satellite calculators

What the model does not guarantee

  • Analytical engineering models do not replace measurements or a mission-specific design review.
  • Spectrum permissions, launch operations and real satellite tracking are outside these calculators.

Worked approach

Radial velocity

Flight time equals path length divided by propagation speed. A ground-to-ground satellite relay has uplink plus downlink path lengths; its round trip doubles that combined flight time. Processing, queuing and TDMA frame delays are additional. A metre-scale laboratory bench cannot demonstrate an orbital delay directly on an ordinary scope.

Common decisions

Questions engineers ask

Which topics does Doppler and Propagation Delay Tool cover?

Radial velocity; Approach and recession; One-way and round-trip delay.

How should I check my work in Doppler and Propagation Delay Tool?

Read the stated assumptions and source references, check units and independently repeat a worked example before relying on the result.

Does Doppler and Propagation Delay Tool operate real satellite equipment?

No. This is a browser-based educational resource. It does not transmit RF signals, command spacecraft or certify a working link.

Related build evidence

Related embedded-system engineering

Aqua Sync is a separate connected-device project, not evidence of a satellite deployment.

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