Hi The gotcha is that you don’t *have* to have a 50 ohm system. An output stage with a narrow band tuned tank is one example of a very “not 50 ohms” system.
There is also a whole debate around the “is 50 ohm source into 50 ohm load really 25 ohms”. That will give you a 3 db delta to bet beers about. The 3 db split of thermal noise between AM noise and PM noise is fairly well accepted, but it still can be challenged. So is the floor -174 - 3 = -177 or is it something else …. If we have a -195.4 dbc/ Hz oscillator that puts out < 18 dbm in a 50 ohm system it’s not -177 or it’s not a 50 ohm system. Bob > On Aug 11, 2016, at 4:47 PM, John Miles <j...@miles.io> wrote: > > Or rather -(177+DUT output power in dBm). The minus sign makes the > difference between the thermal floor and a nuclear war! > > -- john, KE5FX > Miles Design LLC > >> Remember that L(f) is expressed in dBc/Hz, not dBm/Hz. If it were dBm/Hz, >> then kT would be the limit. But in dBc/Hz terms, the limit is 177 + the >> DUT's >> output power in dBm. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
