From: Stefan Jahn <stefan@gr...>  20070513 08:38:49

Am So, 13.05.2007, 10:05, schrieb kochab: Hi! >> I am not sure about the actual problem here. But I can tell two >> things: During AC analysis the AC power sources emit the given >> available power "P" which are set to "0dBm" (1mW) in your example. >> Probably you want to change this. > > The radiometer has to be sensitive to the temperature of the input > load, therefore I regulate the input power by changing the temperature > of the input resistance, which in this case is 200 K. > Then I look only to the noise and not to the signal. Ok. >>The second thing: If DET.s2p >> is meant to be a signal amplifier then have a look at "out.v" instead >> of "out.vn". > > The problem with DET is that it is a nonlinear amplifier, actually a > square law detector, for which I have an experimental transfer > function between input power (W) and output Volts. > Therefore I cannot use the 2 port Sparameters component because it > works between input signal (V) and output signal (V). > Therefore I would need to compute the power, V^2/50 and then apply the > experimental transfer function which characterize the detector. > Is there a way to do this in QUCS? Hm. In fact Sparameters determine ratios of power waves (not voltages!). The S21 (you seem to be interested in this) is proportional sqrt(P2/P1) at given input and output impedance. So I propose to: with given transferfunction: Vout = f(Pin) to normalize Vout to an output power and then convert it to an Sparameter. Does this help?, Stefan. 