EMRFD Message Archive 3070

3070 2009-05-21 07:02:02 Kenneth Stringham dBxxx Relationships Message Date From Subject Joop, It appears that you have a misconception yourself. dBm is always relative to 1mW and is defined for 50 and 600 ohms systems. 50 ohms for most RF applications and 600 ohms for audio applications. dBc is ratio between a Carrier and spurious signal and is always power related. This has nothing to do with Impedance at all, though it is almost always measured using a spectrum analyzer optimized for the termination impedance. In the case of dBv, the value is relative to 1 volt, again no impedance is required, but it is usually measured in the impedance system one is working with at the time. Like dBv, dBmV and dBuV are the same except for the fact they are relative to 1milli-volt and 1 micro-volt. These are all expressions of a ratio between the specified standard and the item being measured expressed as Bel. Ken - AE1X In the broadcast world, we also use dBW (power relative to 1 watt) and dBK (power relative to 1000 watts) Joop, When comparing two signal levels on the same load impedance, there is no meaning to say that it is "voltage related" or "power related". They are both the same number in dB's. if a signal increases by 20dB it means that the voltage increased by a factor of 10 and the power by a factor of 100. So saying that dBuV is related to the signal level of 1uV by "power relation" is meaningless, you get the same calculati Joop, You are wrong. dB whether it is dBm, dBv or whatever is just a pure ratio without dimensions. The suffix gives the meaning of the ratio. I'm a RF chip designer, and for your knowledge, linear blocks at VHF and lower frequencies are measured with dBuV, dBmV even when refering to signal distortion products as third order intercept point. note that f the impedance at connecti I'm not seeing what's incorrect about what Joop said. Power expressed in dBm is a ratio, but it's also an absolute power level. Is 30dBm one watt, or isn't it? Regarding dB with voltage suffixes ... if the definition includes a specific load resistance, then "dBxV" also specify an absolute power level. 73--Nick, WA5BDU