SFDR Calculator

This tool computes the Spurious (or Spur) Free Dynamic Range of a Radio. It is often abbreviated as SFDR and is a key indicator of the linearity of the radio. Enter:

  • Input Third Order Intercept (dBm)
  • Minimum Detectable Signal (dBm)


SFDR = 2/3 * (IP3 – MDS)


The IP3 is a measure of how strong of an input signal the receiver can tolerate before it generates spurs or non-linear products. Ideally the receiver should be operated well below the IP3.

The MDS is the weakest signal that can be detected by a radio. It can be calculated using the Noise Floor Calculator and depends on various factors including the Noise Figure of the receiver.

To maximize the SFDR, the IP3 should be as high as possible and the MDS should be as low as possible. In practice it’s very difficult to meet both these constraints at the same time.

Example Calculation

Using an IIP3 of +10 dBm and a Minimum Detectable Signal of -90 dBm, the SFDR is 66.7 dB.