Documentation sections

Conducted Emissions LC Filter

POSThttps://rftools.io/api/py/v1/calculate

Slug conducted-emissions-filter. Design an LC filter for CISPR 22/FCC conducted emissions compliance. Calculate required inductor and capacitor values for target attenuation.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of conducted-emissions-filter
Name	Unit	Range	Default	Description
emissionLevelnumber	dBμV	at least 0	80	CISPR 22 Class B limit: 66 dBμV at 150 kHz
frequencynumber	kHz	at least 0.1	150	Problem Frequency
targetAttenuationnumber	dB	at least 0	20	Required Attenuation
loadImpedancenumber	Ω	at least 0.1	50	Load Impedance
eSeriesnumber	none	0 … 96	0	Rounds every part to the nearest value in the series; the response and the export are the rounded design's.One of: 0 Ideal values · 12 E12 (10%) · 24 E24 (5%) · 48 E48 (2%) · 96 E96 (1%)

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of conducted-emissions-filter
Field	Unit	Description
requiredF0headline	kHz	Filter Corner Frequency
cValue	μF	Rounded to the part series when one is chosen
lValue	μH	Rounded to the part series when one is chosen
outputLevel	dBμV	Output Emission Level
cornerBuilt	kHz	The corner 1/(2π√(LC)) of the rounded L and C; the required corner with ideal values
attenuationBuilt	dB	What the rounded L and C give at the problem frequency in the same 40 dB/decade model, 40·log₁₀(f/f₀); the required attenuation with ideal values
outputLevelBuilt	dBμV	The measured emission less the attenuation the rounded parts give

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "conducted-emissions-filter",
    "inputs": {
      "emissionLevel": 80,
      "frequency": 150,
      "targetAttenuation": 20,
      "loadImpedance": 50,
      "eSeries": 0
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("conducted-emissions-filter", {
    "emissionLevel": 80,
    "frequency": 150,
    "targetAttenuation": 20,
    "loadImpedance": 50,
    "eSeries": 0,
})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "conducted-emissions-filter",
    "inputs": {
      "emissionLevel": 80,
      "frequency": 150,
      "targetAttenuation": 20,
      "loadImpedance": 50,
      "eSeries": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "conducted-emissions-filter",
	  "inputs": {
	    "emissionLevel": 80,
	    "frequency": 150,
	    "targetAttenuation": 20,
	    "loadImpedance": 50,
	    "eSeries": 0
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "conducted-emissions-filter",
  "values": {
    "requiredF0": 47.43416490252569,
    "cValue": 0.06710561613931607,
    "lValue": 167.7640403482902,
    "outputLevel": 60,
    "cornerBuilt": 47.43416490252568,
    "attenuationBuilt": 20.000000000000004,
    "outputLevelBuilt": 60
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:conducted-emissions-filter",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "emissionLevel": {
          "min": 0,
          "max": null,
          "unit": "dBμV"
        },
        "frequency": {
          "min": 0.1,
          "max": null,
          "unit": "kHz"
        },
        "targetAttenuation": {
          "min": 0,
          "max": null,
          "unit": "dB"
        },
        "loadImpedance": {
          "min": 0.1,
          "max": null,
          "unit": "Ω"
        },
        "eSeries": {
          "min": 0,
          "max": 96,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "emissionLevel": 80,
      "frequency": 150,
      "targetAttenuation": 20,
      "loadImpedance": 50,
      "eSeries": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "emissionLevel"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageConducted Emissions LC Filter, at these values