A Radio Frequency (RF) Link Budget is a summary of all the wireless signal power gains and losses in a communication system.
The link budget equation gives the receive signal power in dBm,
Received power = Transmitted power + Gain (dB) − Loss (dB)
Gain is due to antennas and can be calculated from antenna factor and wavelength.
Gain = GTx + GRx
Loss is due to antenna cable, free space path loss and insertion loss due to adapters and connectors.
Loss = LTx + LRx + LFS
A more detailed equation can be written as
PRx = PTx – LTx – LRx – LFS + GTx + GRx
- PRx = Receive signal power (dBm)
- PTx = Transmit signal power (dBm)
- LTx = Loss from transmitter antenna adapters, cables (dB)
- LRx = Loss from transmitter antenna adapters, cables (dB)
- GTx = Transmit antenna gain (dBi)
- GRx = Receive antenna gain (dBi)
- LFS = Free space path loss (dB)
The link budget calculator is a useful tool that gives the signal level in dBm or Watt at the receiver. This is useful in predicting whether a signal can be demodulated.
💡 Knowing the signal level alone is not enough to predict whether it can be demodulated. It’s also important to know the noise level at the receiver. With this the signal-to-noise ratio (SNR) can be computed.
As the SNR is increased, the signal quality improves. In other words, more bits can be transmitted across the wireless link. Use this calculator to estimate the throughput as a function of SNR. For a fixed bandwidth, increase the SNR to see how the throughput (bps/kbps/Mbps) increases.
Example Link Budget Calculation
Here is an example for wireless communication.
Assume the following parameters:
- PTx = +30 dBm (1 Watt)
- LTx = 1 dB
- LRx = 1 dB
- GTx = 0 dBi (for an Omni-directional antenna)
- GRx = 11 dBi (for a directional Yagi-Uda antenna)
- LFS = 80 dB
Enter these numbers into the calculator gives
- PRx = -41 dBm
🤔 Is this a good enough received signal power?
To answer this question, we have to find the receiver sensitivity. There are three relevant parameters:
- Receiver noise figure
- SNR requirement for a specified performance level
Assuming NF = 30 dB and a bandwidth of 100 MHz, and SNR requirement of 12 dB, the receiver sensitivity is -59 dBm. This is the minimum signal level required to demodulate the signal.
✅ Since the received signal level is -41 dBm, there should be no problem processing this signal.
This is a similar type of analysis that goes into the planning of wireless networks such as 5G and Wi-Fi. Use this tool for example to find the Wi-Fi received signal strength PRx in an indoor environment.
According to Wi-Fi hardware manufacturers, a signal level greater than -65 dBm is good enough. For high bandwidth applications like streaming however, our calculation indicates that it’s a good idea to target -50 dBm for moderate internet connectivity speed.
 Link Budget on Wikipedia