{ "openapi": "3.1.1", "info": { "title": "Ohmforge RF Calculator: Antenna, Link Budget & VSWR API", "version": "1.0.0", "summary": "Dipole and quarter-wave lengths, free-space path loss and link margin, VSWR ↔ return loss.", "description": "Every endpoint performs the same calculation as the human page and returns inputs, result, units, assumptions, sources, warnings and computedAt. MCP endpoint: /mcp." }, "servers": [ { "url": "https://ohmforgerfcalculator.usefulweb.app" } ], "paths": { "/api/v1/calculate": { "post": { "operationId": "calculate", "summary": "Dipole and quarter-wave lengths, free-space path loss and link margin, VSWR ↔ return loss.", "description": "Three everyday radio calculations in one place: antenna element lengths for a frequency (half-wave dipole, quarter-wave monopole, coax stubs), a Friis link budget with free-space path loss, received power, margin and the maximum range for the fade margin you want, and the conversions between VSWR, return loss, reflection coefficient and mismatch loss — also straight from a load impedance.\n\nMethodology:\n- Wavelength λ = c/f with c = 299 792 458 m/s. Half-wave dipole = λ/2 × k × VF and quarter-wave monopole = λ/4 × k × VF, where k is the end-effect factor (0.95 reproduces the ARRL rule 468/f(MHz) ft within 0.2 %) and VF the velocity factor of the element. Coax stubs use the cable's velocity factor. All lengths are starting points: trim the real antenna with an analyser.\n- Free-space path loss FSPL = 20·log10(4π·d·f/c) between isotropic antennas (ITU-R P.525). Friis link budget: received power = Ptx − Ltx + Gtx − FSPL − Lother + Grx − Lrx; margin = received power − sensitivity. The maximum range is the free-space distance at which the margin equals the fade margin you ask for.\n- The first Fresnel zone radius at mid-path is ½·√(λ·d); keeping 60 % of it free of obstacles is the usual rule for line-of-sight links.\n- Mismatch: |Γ| = (VSWR − 1)/(VSWR + 1) = 10^(−RL/20); Γ = (ZL − Z0)/(ZL + Z0) for a load impedance; mismatch loss = −10·log10(1 − |Γ|²); reflected power = |Γ|².\n\nFree-space values: real links lose more to the ground, buildings, foliage and multipath, and the received power fluctuates (fading). Transmit power and antenna gain limits are set by your country's radio regulations — this calculator gives no licensing or legal advice.", "tags": [ "apps" ], "x-mcp-tool": "ohmforge_rf_calculator", "x-owner-app": "ohmforge", "requestBody": { "required": true, "content": { "application/json": { "schema": { "$ref": "#/components/schemas/OhmforgeRfCalculatorInput" }, "examples": { "example1": { "summary": "Wi-Fi link: 2.4 GHz over 100 m", "value": { "mode": "link", "frequencyMHz": 2400, "distanceM": 100, "txPowerDbm": 20, "txGainDbi": 2, "rxGainDbi": 2, "txCableLossDb": 1, "rxCableLossDb": 1, "sensitivityDbm": -90, "fadeMarginDb": 10 } }, "example2": { "summary": "Dipole for the 20 m band (14.2 MHz)", "value": { "mode": "antenna", "frequencyMHz": 14.2, "endEffect": 0.95, "velocityFactor": 1, "cableVelocityFactor": 0.66 } }, "example3": { "summary": "VSWR 2:1 → return loss and mismatch loss", "value": { "mode": "mismatch", "mismatchFrom": "vswr", "value": 2 } }, "example4": { "summary": "75 Ω antenna on a 50 Ω radio", "value": { "mode": "mismatch", "mismatchFrom": "impedance", "loadR": 75, "loadX": 0, "z0": 50 } } } } } }, "responses": { "200": { "description": "Calculation result envelope.", "content": { "application/json": { "schema": { "$ref": "#/components/schemas/OhmforgeRfCalculatorResult" } } } }, "400": { "description": "Malformed JSON body.", "content": { "application/problem+json": { "schema": { "$ref": "#/components/schemas/Problem" } } } }, "422": { "description": "Invalid input (see errors[]).", "content": { "application/problem+json": { "schema": { "$ref": "#/components/schemas/Problem" } } } }, "429": { "description": "Rate limit exceeded (see Retry-After).", "content": { "application/problem+json": { "schema": { "$ref": "#/components/schemas/Problem" } } } } } } }, "/api/v1/tool": { "get": { "operationId": "getToolDefinition", "summary": "Inputs, output schema and examples for this tool", "responses": { "200": { "description": "Tool definition.", "content": { "application/json": { "schema": { "type": "object" } } } } } } } }, "components": { "schemas": { "Problem": { "type": "object", "description": "RFC 9457 problem details. 422 responses include per-field `errors`.", "required": [ "type", "title", "status", "detail" ], "properties": { "type": { "type": "string" }, "title": { "type": "string" }, "status": { "type": "integer" }, "detail": { "type": "string" }, "code": { "type": "string" }, "errors": { "type": "array", "items": { "type": "object", "required": [ "field", "message" ], "properties": { "field": { "type": "string" }, "message": { "type": "string" } } } } } }, "OhmforgeRfCalculatorInput": { "type": "object", "additionalProperties": false, "properties": { "mode": { "title": "Calculation", "type": "string", "enum": [ "link", "antenna", "mismatch" ], "default": "link" }, "frequencyMHz": { "title": "Frequency", "description": "Antenna lengths and link budget.", "type": "number", "minimum": 0.000001, "maximum": 1000000, "default": 2400, "x-unit": "MHz" }, "distanceM": { "title": "Distance", "description": "Link budget: distance between the antennas.", "type": "number", "minimum": 0.001, "maximum": 10000000000, "default": 100, "x-unit": "m" }, "txPowerDbm": { "title": "Transmit power", "description": "20 dBm = 100 mW, 30 dBm = 1 W.", "type": "number", "minimum": -200, "maximum": 100, "default": 20, "x-unit": "dBm" }, "txGainDbi": { "title": "Transmit antenna gain", "type": "number", "minimum": -50, "maximum": 80, "default": 2, "x-unit": "dBi" }, "rxGainDbi": { "title": "Receive antenna gain", "type": "number", "minimum": -50, "maximum": 80, "default": 2, "x-unit": "dBi" }, "txCableLossDb": { "title": "Transmit cable and connector loss", "type": "number", "minimum": 0, "maximum": 200, "default": 0, "x-unit": "dB" }, "rxCableLossDb": { "title": "Receive cable and connector loss", "type": "number", "minimum": 0, "maximum": 200, "default": 0, "x-unit": "dB" }, "otherLossDb": { "title": "Other losses", "description": "Walls, bodies, foliage, polarisation mismatch, rain — whatever free space does not include.", "type": "number", "minimum": 0, "maximum": 300, "default": 0, "x-unit": "dB" }, "sensitivityDbm": { "title": "Receiver sensitivity", "description": "Weakest signal the receiver decodes at the data rate you use (datasheet).", "type": "number", "minimum": -250, "maximum": 50, "default": -90, "x-unit": "dBm" }, "fadeMarginDb": { "title": "Fade margin you want", "description": "Reserve for fading and obstacles; the maximum range is computed for it.", "type": "number", "minimum": 0, "maximum": 100, "default": 10, "x-unit": "dB" }, "endEffect": { "title": "End-effect factor (antenna)", "description": "Shortening of a thin wire element because of the end capacitance; 0.95 is the usual approximation (thicker elements need less).", "type": "number", "minimum": 0.5, "maximum": 1, "default": 0.95 }, "velocityFactor": { "title": "Velocity factor of the element (antenna)", "description": "1 for bare wire in air; insulated wire about 0.95–0.98.", "type": "number", "minimum": 0.1, "maximum": 1, "default": 1 }, "cableVelocityFactor": { "title": "Velocity factor of the coax (stubs)", "description": "Solid PE coax (RG-58, RG-213) 0.66, foam PE about 0.80–0.85.", "type": "number", "minimum": 0.1, "maximum": 1, "default": 0.66 }, "mismatchFrom": { "title": "You know (mismatch)", "type": "string", "enum": [ "vswr", "returnLoss", "gamma", "impedance" ], "default": "vswr" }, "value": { "title": "Value (VSWR, return loss or |Γ|)", "description": "VSWR ≥ 1, return loss in dB as a positive number, or |Γ| from 0 to 1.", "type": "number", "minimum": 0, "maximum": 1000000, "default": 2 }, "loadR": { "title": "Load resistance R", "description": "Mismatch from a load impedance.", "type": "number", "minimum": 0, "maximum": 1000000000, "default": 75, "x-unit": "Ω" }, "loadX": { "title": "Load reactance X", "description": "Positive = inductive, negative = capacitive.", "type": "number", "minimum": -1000000000, "maximum": 1000000000, "default": 0, "x-unit": "Ω" }, "z0": { "title": "Reference impedance Z0", "type": "number", "minimum": 0.001, "maximum": 1000000, "default": 50, "x-unit": "Ω" } }, "required": [] }, "OhmforgeRfCalculatorResult": { "type": "object", "additionalProperties": false, "required": [ "schemaVersion", "tool", "computedAt", "inputs", "summary", "result", "units", "assumptions", "sources", "warnings", "presentation", "links" ], "properties": { "schemaVersion": { "type": "string", "const": "1.0" }, "tool": { "type": "object", "additionalProperties": false, "required": [ "id", "name", "version" ], "properties": { "id": { "type": "string" }, "name": { "type": "string" }, "version": { "type": "string" } } }, "computedAt": { "type": "string", "format": "date-time" }, "inputs": { "type": "object", "description": "Normalised inputs actually used, including applied defaults." }, "summary": { "type": "string" }, "result": { "type": "object", "required": [ "mode", "antenna", "link", "mismatch" ], "additionalProperties": false, "properties": { "mode": { "type": "string", "enum": [ "antenna", "link", "mismatch" ] }, "antenna": { "type": [ "object", "null" ], "additionalProperties": false, "properties": { "frequencyHz": { "type": "number" }, "wavelengthM": { "type": "number" }, "endEffect": { "type": "number" }, "velocityFactor": { "type": "number" }, "cableVelocityFactor": { "type": "number" }, "shortening": { "type": "number" }, "halfWaveElectricalM": { "type": "number" }, "dipoleLengthM": { "type": "number" }, "dipoleLegM": { "type": "number" }, "quarterWaveMonopoleM": { "type": "number" }, "rule468M": { "type": "number" }, "fullWaveLoopM": { "type": "number" }, "quarterWaveStubM": { "type": "number" }, "halfWaveStubM": { "type": "number" } } }, "link": { "type": [ "object", "null" ], "additionalProperties": false, "properties": { "frequencyHz": { "type": "number" }, "distanceM": { "type": "number" }, "wavelengthM": { "type": "number" }, "fsplDb": { "type": "number" }, "eirpDbm": { "type": "number" }, "rxPowerDbm": { "type": "number" }, "rxPowerW": { "type": "number" }, "sensitivityDbm": { "type": "number" }, "marginDb": { "type": "number" }, "fadeMarginDb": { "type": "number" }, "maxRangeM": { "type": "number" }, "maxRangeNoMarginM": { "type": "number" }, "fresnelRadiusM": { "type": "number" }, "fresnel60M": { "type": "number" }, "meetsFadeMargin": { "type": "boolean" }, "lines": { "type": "array", "items": { "type": "object", "additionalProperties": false, "properties": { "item": { "type": "string" }, "db": { "type": "number" }, "levelDbm": { "type": "number" } } } }, "distanceTable": { "type": "array", "items": { "type": "object", "additionalProperties": false, "properties": { "distanceM": { "type": "number" }, "rxPowerDbm": { "type": "number" }, "marginDb": { "type": "number" } } } } } }, "mismatch": { "type": [ "object", "null" ], "additionalProperties": false, "properties": { "from": { "type": "string" }, "gammaMagnitude": { "type": "number" }, "gammaReal": { "type": [ "number", "null" ] }, "gammaImag": { "type": [ "number", "null" ] }, "gammaAngleDeg": { "type": [ "number", "null" ] }, "vswr": { "type": [ "number", "null" ], "description": "null = infinite (total reflection)." }, "returnLossDb": { "type": [ "number", "null" ], "description": "null = infinite (perfect match)." }, "mismatchLossDb": { "type": [ "number", "null" ] }, "reflectedPercent": { "type": "number" }, "transmittedPercent": { "type": "number" }, "z0": { "type": [ "number", "null" ] } } } } }, "units": { "type": "object", "additionalProperties": { "type": "string" } }, "assumptions": { "type": "array", "items": { "type": "string" } }, "sources": { "type": "array", "items": { "type": "object", "additionalProperties": false, "required": [ "title" ], "properties": { "title": { "type": "string" }, "url": { "type": "string" }, "publisher": { "type": "string" }, "retrievedAt": { "type": "string" }, "note": { "type": "string" } } } }, "warnings": { "type": "array", "items": { "type": "string" } }, "presentation": { "type": "array", "items": { "type": "object" }, "description": "Display blocks used by the human page (same data)." }, "links": { "type": "object", "additionalProperties": false, "required": [ "human", "api", "openapi", "methodology" ], "properties": { "human": { "type": "string", "format": "uri" }, "api": { "type": "string", "format": "uri" }, "openapi": { "type": "string", "format": "uri" }, "methodology": { "type": "string", "format": "uri" } } } } } } } }