Let’s say for example that you bought one of our DIGIAIR signal meters. It’s a great tool for people who need to measure antenna signals all the time because it’s very, very accurate. The measurements it takes, however, are in decibel microvolts, usually abbreviated dBμV or dBuV. That’s all well and good if you are just trying to keep relative measurement. However, one of the most common antenna web sites, tvfool.com, gives power measurements in decibel milliwatts, or dBm. How can you convert?
First of all, a bit of explanation: dBμV measures voltage, which is independent of the impedance on the line. dBm measures wattage, so you must know the impedance of the line. In most cases the cables you’re using for antennas are 75Ω (75 ohm) so let’s talk about those conversions.
See, using dB (decibels) as a measurement of anything makes conversion very simple because instead of multiplying, you add. That’s the magic of the whole system. So, to convert from dBμV to dBm, subtract precisely 108.76. You’ll most likely get a negative number… that’s ok you expect that.
Conversions to other systems are also pretty simple. Just find out what you want to convert and use the appropriate rule below. Note that all of these are for 75 ohm cable.
dBmV = 48.75 + dBm
dBmV = dBµV – 60
dBµV = 60 + dBmV
dBµV = 108.75 + dBm
dBm = dBµV – 108.75
dBm = dBmV – 48.75
Using one of those rules, you can easily convert between the three standards used for signal levels. It’s simple!