Receiver sensitivity and MDS calculator

Why sensitivity does not matter on HF

A receiver's own noise is one thing; the noise arriving from the antenna is another. On forty metres the atmospheric and man-made noise is tens of decibels above anything the receiver contributes, and fighting for tenths of a decibel there is pointless. At 144 MHz the picture is reversed. The calculator shows both figures side by side.

The receiver noise floor against the external noise

What to compute	Sensitivity from the noise figureNoise figure from a quoted sensitivity
IF filter bandwidth	CW narrow — 250 HzCW — 500 HzSSB — 2400 HzSSB wide — 3 kHzAM — 6 kHzFM narrow — 12 kHzFM — 15 kHzWFM — 200 kHzFT8 — 50 Hz
Bandwidth, manual (Hz)
Receiver noise figure (dB)
Required signal-to-noise ratio (dB)
Frequency for estimating external noise (MHz)
Location	Quiet rural siteResidential areaCity
Result
Receiver noise floor (MDS)
Sensitivity at the given S/N
Noise figure

📐 The formulas

The noise floor:

P_noise[dBm] = −174 + 10·log10(BW[Hz]) + NF
MDS = P_noise          (signal equals noise, S/N = 0 dB)
Sensitivity = MDS + the required S/N

−174 dBm/Hz is kT at 290 K.

Conversion to a voltage across 50 Ω:

U = √( 50 · 10^((P − 30)/10) )

External noise is taken from the ITU-R P.372 table as the excess Fa over kT₀B.

Check points:

Bandwidth	NF	S/N	MDS	In microvolts
500 Hz	3 dB	0	−144.0 dBm	0.0141 µV
2400 Hz	6 dB	0	−134.2 dBm	0.0436 µV
12 kHz	6 dB	12 dB	−115.2 dBm	0.39 µV

Where this calculator stops:

• The bandwidth is that of the IF filter, not of the band or the antenna
• The external noise table is an ITU-R average: the real level at your house may be 10–20 dB worse
• The antenna's noise temperature and the feedline loss ahead of the receiver are not accounted for
• A manufacturer's quoted sensitivity is often given for a different S/N or bandwidth — check the conditions

🎯 In practice

• Checking a quoted sensitivity: the reverse mode works out the NF from “0.2 µV at 10 dB”.
• Comparing bands: why a preamplifier is unnecessary on 160 m and necessary at 432 MHz.
• Choosing a filter bandwidth: moving from SSB to CW buys 7 dB for nothing.

Practical advice:

1. If band noise with the antenna connected is noticeably louder than with a 50 Ω load, you have sensitivity to spare.
2. A narrow filter beats any preamplifier: it cuts the noise along with the bandwidth.
3. On HF a 10 dB attenuator often costs nothing in reception while noticeably improving overload resistance.
4. On VHF and above, read this calculator together with the cascade noise figure one.

© 2026 UR3PKI · CyberDev.Space · Content licensed under CC BY-NC-SA 4.0.

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UR3PKI. «Receiver sensitivity and MDS calculator». CyberDev.Space. https://cyberdev.space/en/radio/calculators/others/sensitivity (licence CC BY-NC-SA 4.0).

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