You should fool around a bit with the rtl_power utility, part of the basic rtl-sdr install.. However, you'll soon find that it really can only give you a relative measurement on many signals. The algorithms it uses for gain adjustment are not fully known. The dynamics of how it adjusts itself are not favorable to that kind of measurement. Someone else could probably explain how it works better than I. Longish time constants are also involved at a level thats not accessible to the receiver's user.
Also, 1.8 v. peak to peak - if it was a radio signal (which would be more of an approximation of a sine wave) would be several orders of magnitude stronger than most of the signals a TV receiver is used to. That said, I have been able to get signals that strong out of HF bands, using a high-Q magnetic loop, a tuned circuit resonant on that frequency, which acts as a preselector also, only letting that frequency through, so they are not unheard of, (unfortunately, because signals that strong overload receivers).
Few receivers- certainly not the one in the RTL2832 chip in direct sampling mode, which is not capable of that much dynamic range, can handle that much voltage without being completely overloaded.
So you absolutely have to attenuate them, a lot. You can make a L-pad with a variable potentiometer, it doesnt have to be fancy. If you do that, when you need to, you can handle both strong and weak signals, by riding the gain. That can work pretty well.