PDF of this tutorialTxp = transmitter output power in dBm
CL = channel combiner losses in dB
TLL = total transmission line loss in dB
TAG = transmit antenna gain in dBi
PL = free space path loss in dB = 96.6 +20 Log (frequency in GHz) + 20 Log (distance in miles)
RAG = receive antenna gain in dBi
BDCG = block downconverter gain in dB
RLL = total receive line loss in dB
NF = thermal noise floor (-108 dB)
nf = noise figure of receive system (2.6 dB typical)
FM = fade margin (15 dB typical)
The critical design factor for a digital system is the required signal-to-noise ratio (SNR) of the receiver. For this case, 25 dB S/N. Fade margin is an estimated value that will vary at each site. Factors that can contribute to fade include heavy rain, multipath, terrain, and foliage blockage.
Signal Strength Link Budget
Txp - CL - TLL + TAG - PL - FM + RAG + BDCG - RLL = signal strength @ rx site in dBm
S/N Link Budget
Txp - CL - TLL + TAG - PL - FM + RAG - nf - NF = S/N @ rx site in dB
Note that this calculation applies for a modem with 2-MHz channels and 4.5 dB transmitter additional headroom to allow for the transmission of the peak signal arising from three modulators on one channel. The numbers vary for a single modulator and for more subchannels.
*This module provided courtesy of the ITS division of ADC.
