On Thu, Feb 11, 2021 at 06:43 PM, bigusmith wrote:

I am not used to dealing with RF output power in Decibels instead of watts

Get used to it, you'll find dB very useful.? There are lots of things in radio - and pretty much any kind of electronics - that aren't convenient to measure in watts.? If your transmitter puts out 100 watts, and you run it into a linear amplifier that puts out 1000 watts, I suppose you could say the gain of the amplifier is 900 watts, but then what if you only ran 50 watts into the amplifier?? You can't say the gain is 900 watts, therefor the output will be 950 watts, it just ain't so.? But if we say the gain of the amplifier is 10 log(1000 watts/100 watts) = 10 dB, we have something we can work with. 10 dB is a power gain of 10 times, so our amplifier will put out 500 watts with 50 watts in.

And what is the sensitivity of your receiver in watts?? Well, if you ran any amount of watts into your receiver, all you'd get out of it is smoke.? Watts doesn't work here.? So we measure receiver sensitivity in dBm -? that is, dB relative to one milliwatt.? A typical receiver might have a sensitivity of -120dBm.? If we put a 30 dB attenuator in line, the combination now has a sensitivity of -90 dBm.? Suppose you have a receiver with a sensitivity of -120 dBm at your house, and there's a transmitter up on a nearby hill, what is the path loss in watts?? Doesn't make sense. However, you could say that the path loss is 100 dB, that's a number that would make sense.?? Then if you had a 10 watt (+40 dBm) transmitter up on the hill, you could calculate that the power at your receiver is (40 dBm - 100 dB path loss) = -60 dBm, and your receiver would hear that just fine.

So, there are lots of things that aren't measured or expressed well in watts, but if we use dB (or dBm) can easily be measured or expressed.? And that's why so many things in electronics are expressed in dB, or in dB relative to some value.

If you're wondering why the B in dB is capitalized, it's because the "Bel" was named after Alexander Graham Bell, and Bell being a proper name, we capitalize it.? We should also capitalize Volts, Watts, Ohms - all come from somebody's name -? and a bunch of others, but we get sloppy and often don't bother.