In this post we calculate the sensitivity of an FM Radio Receiver.
What is Sensitivity?
Sensitivity is the minimum signal that can be detected by a receiver. It depends on noise figure and minimum required Signal-to-Noise Ratio. The SNR in turn depends on the modulation format. Typically the SNR increases with the complexity of modulation.
FM Sensitivity Values in dBm, Volt and dBf
The sensitivity of an FM tuner is sometimes specified in dBf (deciBel relative to Femtowatt). For instance the Clarion tuner has a sensitivity of 8 dBf. A level between 8 dBf and 12 dBf is considered very good.
Use the dBf to dBm calculator to find that this equates to -112 dBm.
-112 dBm converts to
- 0.56 μV for a 50 ohm impedance
- 0.69 μV for 75 ohm
Sensitivity of FM chips
It’s difficult to find the sensitivity numbers in many of the FM data sheets that we came across online. However the Si4720 is an exception.
Below is an excerpt from the data sheet
The sensitivity in a 50 ohm system with an SNR of 26 dB is 1.1 μV. This converts to -106 dBm. Using the dBm to dBf calculator, the equivalent is 14 dBf.
The sensitivity for Radio Data System operation is 15 μV which equates to -83 dBm or 37 dBf.
Summary
We have discussed the sensitivity of FM chips and demonstrated how to use our calculators to find values in uV, dBm and dBf.