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You could start off with a signal measured in dBm, perhaps
the output of a transmitter. Thereafter you could add and subtract anything in dB (but NOT dBm). Here's an example (my figures are made-up and not intended to be realistic). let us calculate the E-M-E signal strength of our transmission bounced off the moon. TX output = 1000W = 60dBm. Antenna gain (Assume a big dish) = 50dB Effected Radiated Power (ERP) = 110dBm Path loss to Moon = 80dB Path loss due to bouncing off Green Cheese = 30dB Path loss back from Moon = 80 dB again Total path loss = 190dB Antenna Gain = 50dB Received Signal Strength = 110 -190 + 50 = -30dBm = 1 uWatt. So, we started off with dBm, then added or subtracted dB (which gave us dBm again, but we only added or subtracted dB) "jason" wrote in message ups.com... So from what you have all explained, can I bold enough to say that I can add any value in db and any value in dbm together without converting to one db or dbm unit because they are in the ratio form and having virtually the same 10log (P1/P2) formula and nothing else more?? |