![]() Note that this is a moot point, because it does not make sense to use either the AC simulation or the digital source in this application. ![]() Your digital pulse would never even turn on during the simulated time/frequency window. Is that actually where you intend your design to operate? Importantly, your digital source creates a pulse of 1 ms length, but one period at your lowest simulation frequency (1 GHz) is only 1 ns (0.001 ms). Your AC simulation is from 1 GHz - 10 GHz, which is quite a high frequency and wide frequency range.In this configuration, the amplifier will essentially not function. Meanwhile the load has a very high (1 MΩ) impedance. In this case, the source S1 is a digital source, with an extremely low impedance. The amplifier (X1) expects a 50Ω impedance on its source and load.You probably want to use an AC voltage source instead of the digital pulse source. This does not really make sense for use with an amplifier. The source to your circuit (S1) is a digital pulse source."AC simulation" will not work, as the calculations are done in the frequency domain (you would get a plot of voltage vs. By this, I think you mean that you want a plot of the voltage as a function of time? For this, you will need to use a "transient simulation". You mention that you want an "oscilloscope style" output from the simulation. ![]() I have only used QUCS a handful of times, but I can see several issues with this simulation setup: ![]() But there are also other oddments you should know such as circulators, directional couplers, waveguide types and modes, etc. Many are "radio" models (this is where ARRL pubs are useful even for digital SDR). Low frequency lumped circuits have these but there are a whole other set for RF/µW. Learn the system level architectures and circuit level design patterns. SPICE is fundamentally a lumped model simulator only. SPICE's closest approximation to distributed modeling are transmission line devices which don't actually do things like s-parameter types of transmission/reflection you have to go to sim tools like Agilent's ADS or other harmonic balance simulators like Qucs to really have meaningful simulation capability. Get familiar about things like return loss, source mismatch and noise figure which come up all the time as "fundamentals" akin to KVL/KCL or mesh analysis in lumped model circuits. Getting familiar with "distributed model" as this trumps lumped model elements in RF/µW circuits. I'd done ham radio and even worked with radar systems for the Navy but I had gaps. I really solidified my RF/µW knowledge working for HP T&M (divorced/remarried as Agilent, soon to be divorced/remarried as Keysight). Find a lab at school that has these if possible. This means having access to certain equipment like VNAs and SAs plus a lot of the connector and calibration paraphernalia (which is $$$). Testing things (without the right test equipment building things can be hit-or-miss - which is how RF/µW gives the illusions of being "black art"). So this circuit can be used in place anywhere that calls for a quarter-wave transmission line.ġ This pi network makes a low pass filter, which can be a nice side-effect since it reduces harmonic distortion.Building things - NOTHING in engineering is meaningful without building things and verifying their operation empirically. Let's run a time-domain simulation:īingo! The impedance transforming properties of a quarter wave transmission line are also preserved: if the output is open, the source will see a short, and so on. If this is indeed a quarter-wave transmission line, we should see R1 90 degrees out of phase with the input. So now the circuit with real values, terminated with an 86 ohm load: It can be done! Remember that a transmission line consists of some self-inductance per unit length, and some capacitance per unit length, and the ratio of these determines the line's characteristic impedance:
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