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Run npx skillmds@latest add ashfordeou/communication-link-budget in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

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Is Communication Link Budget free to use?

Yes. Installing skills from SkillMD is free. This skill is licensed under Apache-2.

Who published Communication Link Budget?

ashfordeOU (@ashfordeou) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Communication Link Budget by ashfordeou

Name: Communication Link Budget
Author: ashfordeOU

Communication Link Budget

Use when you must build or check a spacecraft communications link budget: compute the free space path loss from distance and frequency, derive EIRP from transmit power and antenna gain, estimate received power and carrier to noise density ratio, and verify the link margin against the required energy per bit to noise ratio at the data rate. Produces path loss, EIRP, received power, C/N0, Eb/N0, and the margin verdict that closes the link. Trigger: link budget, path loss, eirp, carrier to noise density, eb n0, link margin, data rate, spacecraft communications.

ashfordeOU Updated Sep 17, 2026

File contents

Spacecraft Communication Link Budget (space-systems/subsystems/communication-link-budget)

Use when the task is a spacecraft communications link budget: Friis free-space path loss, EIRP, received power, carrier to noise density ratio, and the Eb/N0 margin at the data rate.

Units convention (stated once): power and EIRP in dBW, gains and losses in dB, distance in meters, frequency in hertz, noise temperature in kelvin, data rate in bits per second, C/N0 in dB-Hz, Eb/N0 and margin in dB. No Watt/dBW mixing anywhere.

Domain quick reference

Free-space path loss: L_fs = 20log10(4pi*d/lambda) dB, where lambda = c/f with c = 299792458 m/s; doubling distance or frequency adds about 6 dB of loss.
EIRP (dBW) = transmit power (dBW) + transmit antenna gain (dB).
Received power: Pr = EIRP + Gr - L_fs - L_other (dBW), where other losses lump atmospheric, pointing, and polarization effects.
Carrier to noise density: C/N0 = Pr + 228.6 - 10log10(T) dB-Hz (228.6 is 10log10(1/k) with k = 1.380649e-23 J/K); doubling the system noise temperature costs 3 dB.
Eb/N0 = C/N0 - 10*log10(R); the required Eb/N0 comes from the modulation and coding scheme, and the margin is the difference.
ECSS-E-ST-50C (communications) sets the European baseline for space data link budgets; ECSS standards are free to download from https://ecss.nl/standards/ (name + paraphrase + link only).

Workflow

Set the link geometry: slant distance (m) and carrier frequency (Hz); compute free_space_path_loss.
Combine transmit power (dBW) and antenna gain (dB) with eirp_dbw.
Add the receive gain and subtract path and other losses with received_power_dbw.
Convert received power to carrier to noise density with the system noise temperature: cno_db_hz.
Close the budget with link_margin at the data rate against the required Eb/N0; treat ok False as a design failure, not a rounding error.

Pitfalls

Mixing watts and dBW in one chain; convert transmit power to dBW once, then keep everything in dBW.
Feeding kilometers or gigahertz into the Friis formula without converting to meters and hertz.
Dropping other losses (pointing, polarization, atmospheric) and calling a paper link closed.
Checking the margin at the wrong data rate; 10*log10(R) is the per-bit penalty.
Accepting a negative margin because the raw C/N0 still looks large.

Behavior contract (gate 3)

The path loss, EIRP, received power, C/N0, and margin logic is exercised by the gate 3 contract test: scripts/test_link_budget_logic.py against scripts/link_budget_logic.py (stdlib unittest, offline). Run from the repo root: python3 skills/space-systems/subsystems/communication-link-budget/scripts/test_link_budget_logic.py

Compliance

Standards referenced, not reproduced: ECSS standards are freely downloadable (copyright ESA); summary-only per standards-map.yaml and brief 06.
compliance: STANDARDS-REF, gated: false.

---name: communication-link-budgetdescription: Use when you must build or check a spacecraft communications link budget: compute the free space path loss from distance and frequency, derive EIRP from transmit power and antenna gain, estimate received power and carrier to noise density ratio, and verify the link margin against the required energy per bit to noise ratio at the data rate. Produces path loss, EIRP, received power, C/N0, Eb/N0, and the margin verdict that closes the link. Trigger: link budget, path loss, eirp, carrier to noise density, eb n0, link margin, data rate, spacecraft communications.license: Apache-2.0---# Spacecraft Communication Link Budget (space-systems/subsystems/communication-link-budget)Use when the task is a spacecraft communications link budget: Friisfree-space path loss, EIRP, received power, carrier to noise densityratio, and the Eb/N0 margin at the data rate.Units convention (stated once): power and EIRP in dBW, gains andlosses in dB, distance in meters, frequency in hertz, noisetemperature in kelvin, data rate in bits per second, C/N0 in dB-Hz,Eb/N0 and margin in dB. No Watt/dBW mixing anywhere.## Domain quick reference- Free-space path loss: L_fs = 20*log10(4*pi*d/lambda) dB, where lambda = c/f with c = 299792458 m/s; doubling distance or frequency adds about 6 dB of loss.- EIRP (dBW) = transmit power (dBW) + transmit antenna gain (dB).- Received power: Pr = EIRP + Gr - L_fs - L_other (dBW), where other losses lump atmospheric, pointing, and polarization effects.- Carrier to noise density: C/N0 = Pr + 228.6 - 10*log10(T) dB-Hz (228.6 is 10*log10(1/k) with k = 1.380649e-23 J/K); doubling the system noise temperature costs 3 dB.- Eb/N0 = C/N0 - 10*log10(R); the required Eb/N0 comes from the modulation and coding scheme, and the margin is the difference.- ECSS-E-ST-50C (communications) sets the European baseline for space data link budgets; ECSS standards are free to download from https://ecss.nl/standards/ (name + paraphrase + link only).## Workflow1. Set the link geometry: slant distance (m) and carrier frequency (Hz); compute free_space_path_loss.2. Combine transmit power (dBW) and antenna gain (dB) with eirp_dbw.3. Add the receive gain and subtract path and other losses with received_power_dbw.4. Convert received power to carrier to noise density with the system noise temperature: cno_db_hz.5. Close the budget with link_margin at the data rate against the required Eb/N0; treat ok False as a design failure, not a rounding error.## Pitfalls- Mixing watts and dBW in one chain; convert transmit power to dBW once, then keep everything in dBW.- Feeding kilometers or gigahertz into the Friis formula without converting to meters and hertz.- Dropping other losses (pointing, polarization, atmospheric) and calling a paper link closed.- Checking the margin at the wrong data rate; 10*log10(R) is the per-bit penalty.- Accepting a negative margin because the raw C/N0 still looks large.## Behavior contract (gate 3)The path loss, EIRP, received power, C/N0, and margin logic isexercised by the gate 3 contract test:scripts/test_link_budget_logic.py against scripts/link_budget_logic.py(stdlib unittest, offline). Run from the repo root:python3 skills/space-systems/subsystems/communication-link-budget/scripts/test_link_budget_logic.py## Compliance- Standards referenced, not reproduced: ECSS standards are freely downloadable (copyright ESA); summary-only per standards-map.yaml and brief 06.- compliance: STANDARDS-REF, gated: false.

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