The specification for a certain radio receiver says: Typically 12dB SINAD NBFM for 0.15uV at 145MHz. If I understand correctly, this means that the received radio wave should have a voltage level of at least 0.15uV for the receiver to produce a signal with a quality of 12dB SINAD. I know how to calculate the signal power with the link equation, I can also calculate the electric field intensity of the EM wave, but I don't see how I can calculate the voltage level of a signal. How do I verify that my transmitted radio wave will meet this voltage requirement?


2 Answers 2


The specification means $0.15\ \mu\text{V}$ at the input terminals of the receiver, so this voltage across a $50\ \Omega$ load.

Power in a resistor can be calculated with
so $0.15\text{ }\mu\text{V}$ is a power of ${(0.15 \times 10^{-6})^2 } /{50} = 4.5 \times 10^{-16} \text{ W}$ (or ask google)

This is -123.5 dBm into the receiver.

For interest, if the receiver is 25 kHz wide, and needs about 6 dB S/N to achieve that SINAD, then the receiver noise figure is an amazing 3 dB. Put another way, thermal noise at room temperature, in 25 kHz, is already -127 dBm, so the receiver is about as sensitive as it could possibly be for terrestrial communications.


You must also know the impedance of the receiver which is typically 50 ohms. Convert the received signal from dBm to Watts. Then the input voltage is sqrt ( P * R )

We usually work this the other way around: Convert 0.15 uV into 50 Ohms to dBm which is -123.5 dBm. If your signal is greather than that you are Ok. Say your received signal is -100 dBm you have a 23.5 dB fade margin.


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