Documentation sections

Cable Shield Effectiveness

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

Slug cable-shield-effectiveness. Calculate cable shielding effectiveness and transfer impedance vs frequency. Evaluate coaxial and shielded cable EMI performance for EMC compliance.

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 cable-shield-effectiveness
Name	Unit	Range	Default	Description
shieldResistancenumber	mΩ/m	at least 0.001	10	Per metre, from cable datasheet
cableLengthnumber	m	at least 0.01	2	Cable Length
frequencynumber	MHz	at least 0.001	10	Frequency
transferInductancenumber	nH/m	at least 0	0.159155	Per metre, from the cable datasheet or a transfer-impedance measurement. The default puts the inductive corner of a 10 mΩ/m shield at 10 MHz
lineImpedancenumber	Ω	at least 0.1	50	Characteristic impedance of the line inside the shield, which the coupled voltage is compared with
targetSEnumber	dB	0 … 120	40	The shielding effectiveness the cable must reach. The status fails below 20 dB.

Outputs

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

Outputs of cable-shield-effectiveness
Field	Unit	Description
shieldingEffectDbheadline	dB	Shielding Effectiveness
transferImpedance	mΩ	Transfer Impedance

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": "cable-shield-effectiveness",
    "inputs": {
      "shieldResistance": 10,
      "cableLength": 2,
      "frequency": 10,
      "transferInductance": 0.159155,
      "lineImpedance": 50,
      "targetSE": 40
    }
  }'

import rftools

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

result = client.calculate("cable-shield-effectiveness", {
    "shieldResistance": 10,
    "cableLength": 2,
    "frequency": 10,
    "transferInductance": 0.159155,
    "lineImpedance": 50,
    "targetSE": 40,
})
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": "cable-shield-effectiveness",
    "inputs": {
      "shieldResistance": 10,
      "cableLength": 2,
      "frequency": 10,
      "transferInductance": 0.159155,
      "lineImpedance": 50,
      "targetSE": 40
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "cable-shield-effectiveness",
	  "inputs": {
	    "shieldResistance": 10,
	    "cableLength": 2,
	    "frequency": 10,
	    "transferInductance": 0.159155,
	    "lineImpedance": 50,
	    "targetSE": 40
	  }
	}`)
	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": "cable-shield-effectiveness",
  "values": {
    "shieldingEffectDb": 64.9484986639195,
    "transferImpedance": 28.284276304183297
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:cable-shield-effectiveness",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Hähner & Mund, Screening of Cables in the MHz to GHz Frequency Range — Extended Application of a Simple Measuring Method (1998), eqs. 3-1 and 3-2, the method behind IEC 62153-4-4; Vance, IEEE Trans. EMC 17(2), 1975",
    "assumptions": [
      {
        "code": "electrically-short-screen",
        "text": "The screen is electrically short: SE = 20·log₁₀(Z₁/(|Z_T|·l)) holds up to about a sixth of a wavelength, and a longer cable is flagged, not corrected."
      },
      {
        "code": "transfer-impedance-r-plus-jwm",
        "text": "The transfer impedance is R_T + jωM_T; the diffusion term of a solid screen, R₀·γd/sinh(γd), is not modelled, and equals R₀ at low frequency."
      }
    ],
    "validRange": {
      "status": "inside",
      "bounds": {
        "shieldResistance": {
          "min": 0.001,
          "max": null,
          "unit": "mΩ/m"
        },
        "cableLength": {
          "min": 0.01,
          "max": null,
          "unit": "m"
        },
        "frequency": {
          "min": 0.001,
          "max": null,
          "unit": "MHz"
        },
        "transferInductance": {
          "min": 0,
          "max": null,
          "unit": "nH/m"
        },
        "lineImpedance": {
          "min": 0.1,
          "max": null,
          "unit": "Ω"
        },
        "targetSE": {
          "min": 0,
          "max": 120,
          "unit": "dB"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "shieldResistance": 10,
      "cableLength": 2,
      "frequency": 10,
      "transferInductance": 0.159155,
      "lineImpedance": 50,
      "targetSE": 40
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "shieldResistance"
      ],
      "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 pageCable Shield Effectiveness, at these values