What is the received signal level with a transmit power of 10 W (+40 dBm), a transmit antenna gain of 6 dBi, a receive antenna gain of 3 dBi, and a path loss of 100 dB?

To find the received signal level, you simply add all the system gains to your starting transmit power and subtract the path losses. This process is known as calculating the link budget. Start with the transmit power in decibels relative to a milliwatt (+40 dBm). Add the transmit antenna gain (+6 dBi) and the receive antenna gain (+3 dBi) to get an effective radiated power of +49 dBm equivalent. Finally, subtract the path loss of 100 dB. Taking +49 dBm and subtracting 100 dB yields a received signal level of -51 dBm.