The dBm scale requires a stated load impedance (50 ohms for the table above). The 0 references are shown in boldface.The dBm reference is 223.607 millivolts which equals 1 milliwatt into 50 ohms. If you want dBuV, just add 60 to the dBmV numbers. Between dBV and dBmV there's a constant offset of 60. And, Dave requested the voltage-referenced formula.Here's a table showing the dBm, dBV, and dBuV values for voltages from 1 volt to 1 microvolt: Note that between dBm and dBV there's a constant offset of 13. By using a voltage reference, you eliminate this extraneous step. I gave the values for dBV and DBmV in my earlier response.While the dBm scale is commonly used on signal generator dials, it's not as easy to compute this value from measured parameters because you have to know the load impedance and do the power calculation. The dBV, dBmV, and dBuV scales are referenced to 1 volt, 1 millivolt, and 1 microvolt, respectively, and are independent of load impedance. The dBm scale is referenced to 1 milliwatt power into a defined load impedance (50 ohms here). Quote:Originally posted by Peter Bertini.According to my Boonton, around -77dBm should be closeI was trying to avoid this area of confusion.Decibels are always relative to something.
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