There are absolute and relative units.Ībsolute logarithmic units express a physical value referenced to some specific value, for example, dBm is an absolute logarithmic unit of power with reference to 1 mW. Logarithmic units are widely used in science, technology and even in everyday things like photography and music. Log 5(25) = 2 Classification of Logarithmic Units In more simple words, a logarithm is an answer to the question: “How many times do we have to multiply one number to get another number?” For example, how many times do we multiply 5 to get 25? The answer is 2 or In other words, the logarithm is a quantity representing the power to which a fixed number called the base must be raised to produce a given number. The logarithm is the inverse operation to exponentiation. Some people even think that logarithmic values more related to the era of slide rules than to the modern digital world. Looks convenient? Yes, but not to everyone! Actually, all people who are not mathematically or technically inclined can be easily confused when dealing with quantities expressed in logarithmic units like decibels. At the same time, the sound power of quiet conversation is 0.000000001 W or 30 dB SWL. For example, the sound power of a Saturn V rocket is 100,000,000 W or 200 dB SWL (dB referenced to the sound power level 10⁻¹² W, it is described below). Logarithmic units allow representing a very large range of ratios by a small convenient number similar to scientific notation. You can find these used on Ebay by Mini-Circuits, HP, and others.The sound power of a Saturn V rocket is 100,000,000 W or 200 dB SWLĪ logarithmic scale is often used when there is a large range of quantities like sound pressure, earthquake strength, light intensity, various frequency-dependent values like musical intervals, in antenna engineering, electronics, acoustics, RF engineering.
#Microvolts to dbm generator
If all this is confusing, you want to simplify the whole thing, and all you need is 75 ohm - get a 50 to 75 barrel converter, and your generator readings will match what the tuner sees with a very minor loss. In my 50 ohm dBf to uV rms chart, 48 dBf = 56 uVrms. If we add the dummy antenna loss to the what the tuner sees, 40 dBf + 7.8 dB, we get 47.8 dBf. The dummy load loss for this dummy load, Pl, is 7.8 Db. The 50 ohm generator output will need to be to 55 uV, so the tuner sees 40 dBf. Reference pages 11-12 for the dummy antennas. To correlate to the 50 ohm dBf chart I just posted - let's look at the 40 dBf line (page 15) for a 75 ohm dummy antenna (7),(8) shown in (column1). gives Charts of available power, but remember - these are what you will see at the tuner AFTER the dummy antenna, and includes the resistor loss.
explains the "input levels" with reference to important terms used later - open circuit voltage Eo (no load), and dummy antenna antenna loss Pl. It gets a little confusing, as the figures being referenced are below the figure caption line for (1) and (2), but then above the caption line for (3) - (7), then below again for (8). They go one step further, however, and include setups using 2 generators, required for some of the tests in this standard. Pages 11-12 shows dummy antenna setups, using resistors to convert from 50 ohm outputs to either 75 or 300 ohms. The complete set of files for this standard is here in files. At the risk of confusing people further, including me, I'll post the "clear as mud" relevant pages from the IEEE-1975 standard on this topic.
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