Calculate dBm from dBuV without Ohms

Hi,

I've come across many datasheets for RF transmitter ICs where the power output is given in dbuv, but no ohms are given. Is it correct to automatically assume 50ohms when trying to calculate the power in dBm.

In other words, I need to find power in dbm when I am only given dbuv?

Thanks!

Hi. Do you mean dbuv or dBμV ? dBu is meant as voltage unloaded/unterminated; dBμV is referred to 1 microvolt. None is power as dBm referred as 1 milliwatt on 600Ω.
Can be based on 600 Ω; 50Ω; 75Ω impedance or on whatever someone decides to define.

dBuV is a Voltage Level that is usually used in 75 Ohms systems. ( CATV, SMATV etc)

Sensitivity of receivers has been routinely specified in dBμV, the unit is also common in EMI measurements. If it's VHF band or above, you can safely assume 50 ohm reference impedance so that 1 dBμV = -107 dBm.

This is odd. At this point I am almost certain the output power is -8 to -10dbm because I tested a similar device with 118dbuv instead of 121dbuv like the first listed in the datasheet and it outputs roughly the same power. At this point I honestly don't care why as I've moved to the next stage of the project and this is irrelevant, but it still would be interesting to know. If it were 50ohm, it should be way more dbm than that.

How do you measure or specify 118dBuV and 121dBuV ?

If load impedance is constant, power delivered to load is twice for 121dBuV compared to 118dBuV.

dBuv as you state is not power. -8 to -10 dBm is for expressing power, and its voltage will depend on the impedance.

If you want to play with on-line calculators, here is one : ----> http://www.qsl.net/pa2ohh/jsdbmdbu.htm