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Antenna Factor and Field-Strength Measurement Chain

Calculate field strength from receiver reading, antenna factor, cable loss, and preamplifier gain.

FORMULAv1.0.0
INPUT PARAMETERS

Enter single-frequency measurement-chain values

Recover field strength at the antenna from the receiver-port reading. All corrections must use the same frequency.

CALCULATION RESULT

Calculation result

Calculated locally
∿

Enter the parameters and run the calculation to see results and model assumptions here.

FORMULA & TRACEABILITY

Formulas and applicability

Formulas, variables, and model boundaries are published. References last reviewed on 2026-08-28.

3 formulas · 2 references
CORE EQUATIONS

Core equations

These equations directly produce the primary results and define the tool’s core model.

2
F01

Field-strength measurement chain

E = U + AF + L꜀ − Gₚ

Combines receiver reading, antenna factor, cable loss, and preamplifier gain in the logarithmic domain.

E
Electric field strengthdBμV/m
U
Receiver voltage readingdBμV
AF
Antenna factordB/m
L꜀
Cable insertion lossdB
Gₚ
Preamplifier gaindB
Applicability
  • All correction factors correspond to the same frequency
  • Receiver reading is taken after the preamplifier
F02

Linear antenna-factor definition

AF = E / V

Antenna factor is the ratio of incident electric field strength to receiver-terminal voltage.

AF
Linear antenna factor1/m
E
Electric field strengthV/m
V
Receiver-terminal voltageV
Applicability
  • Antenna, receiver impedance, and calibration setup are consistent
DERIVED & CONVERSION

Derived and conversion equations

Derive units, levels, and supporting engineering quantities from the core values.

1
F03

Linear field-strength conversion

E(μV/m) = 10^[E(dBμV/m)/20]

Recover linear field strength from a level referenced to 1 μV/m.

E
Electric field strengthμV/m
Applicability
  • Reference field strength is 1 μV/m
REFERENCES

References

01ITU-R · Recommendation SM.575-3Protection of fixed monitoring stations against nearby or strong transmitters2021 · Gives the E = U + k + αc measurement chain for antenna factor and cable loss.
02NIST · NIST Technical Note 1507Uncertainty Assessment for Standard Antenna Measurements on the Open Area Test Site1998 · Gives antenna-factor calibration equations, cable loss, and receiver corrections.
Engineering use notice

Results use the models and assumptions shown on this page for design estimates and pre-compliance risk review. Complex structures, dispersion, near-field coupling, and test setup can cause significant deviation.

FAQ

Frequently asked questions

What is the antenna factor definition and formula?

AF = E / U, the ratio of incident electric field to receiver-terminal voltage; in logarithmic form, AF(dB/m) = E(dBμV/m) − U(dBμV).

How is the field-strength measurement chain computed?

E = U + AF + cable loss − preamplifier gain, all as log values at the same frequency. Every correction must correspond to the same frequency point.

How is a theoretical antenna factor estimated?

For a passive reciprocal antenna conjugately matched to 50 Ω, AF(dB/m) ≈ 20·log₁₀(f_MHz) − G(dBi) − 29.78 in free space. The theoretical value never replaces calibrated data.

PRE-COMPLIANCE SUPPORT

Need accredited testing or pre-compliance support?

These tools support design-stage estimates. For accredited EMC testing, compliance decisions, and troubleshooting, contact us.

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