# Questions tagged [qucs]

For questions about the Quite Universal Circuit Simulator (QUCS) open source circuit simulator package.

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### How do I find the -3dB point on a given graph

I just performed an AC Simulation on QUCS and was asked to find values of gain and phase at low freq. and high freq and at the -3dB frequency point with the roll-off slope. The circuit is an RC ...
0answers
10 views

### simulate a thyristor triggered load having a RC branch

In the following picture you have a simulation to figure out the voltage on a Thyristor triggered load. The current of triggering on the thyristor gate is 300 mA. What I am looking for is a signal on ...
1answer
38 views

### Diode doesn't work in a [attempt of] power supply simulation with QUCS

As a simulation exercise, I am trying to work out a power supply and actually I am at the point provided in the figure below There is a message of error which I don't understand, but I realized it ...
1answer
146 views

### Non-inverting UA741 opamp simulation on QUCS

According with instructions provided here https://www.youtube.com/watch?v=dBY1k5qK2w4 (in Spanish), I tried to simulate an inverting opamp configuration, but I couldn't figure out the right vout ...
0answers
82 views

### Trying to build a latch circuit on Qucs using BJT transistors. I can't find what is wrong

I seem to be able to get it to work on CircuitLab: simulate this circuit – Schematic created using CircuitLab However I can't, for the life of me, find a way to build the same thing on Qucs. I ...
2answers
243 views

### Qucs simulation of quarter wave microstrip stub doesn't match ideal calculaton

I'm trying to simulate the resonant frequency and insertion loss of a 3 mm open stub on a 10 mm microstrip transmission line (50 Ω) on a FR-4 PCB (εr = 4.0, height = 0.1 mm). I calculated that the ...
1answer
145 views

### RF amplifier biasing in QUCs

I have selected an infineon BFP840ESD BJT to work with in the design of a low noise RF amplifier. I'm trying to use Qucs Studio to simulate it. From the datasheet I select my bias conditions with as ...
1answer
26 views

### Problem adding tranformer to QUCS schematic when simulating with ngspice

I'm having problems simulating the following circuit using ngspice alongside Qucs. The main problem I can see in log is that is acusing an singular matrix. I imagine the problem is related to how ...
3answers
84 views

### Different readings of voltmeter on simple circuit

Hi I am trying to learn the basics of electronics and puzzled by the following qucs simulation. Why the readings of voltmeters are different? I would expect, by the way zero readings on both ...
1answer
241 views

### Common-Emitter NPN Transistor Amplifier Simulation Failed

I'm trying to simulate a simple common-emitter transistor amplifier presented as an example in Practical Electronics for Inventors in Qucs. The circuity is identical to the one presented in the book. ...
1answer
543 views

### Simulation discrepancy in Qucs with 2N3904 transistor

I've been testing out a few circuit simulation applications and ran into an unusual issue with Qucs and the 2N3904 transistor. For a simple NPN transistor circuit with load resistor $R_L$, base ...
0answers
79 views

### NFC Antenna matching

I am trying to follow the TI document on NFC antenna matching for the TFR7970A chipset. http://www.ti.com/lit/an/sloa241b/sloa241b.pdf I am under linux, and while I could try wine to use the smith ...
1answer
171 views

### Resistance or conductance of resistor networks

I am trying to figure out if the equivalent resistance (or similarly conductance) of a resistor network can be calculated using Qucs (as opposed to solving the Kirchhoff equations directly, or doing ...
1answer
37 views

### Why is there no variation caused by this swept parameter?

I quite like Qucs now that I more or less have the hang of it. Unfortunately, I can't figure out how to get a parametric sweep working. I'm running an AC simulation on this circuit: For now I'm not ...
1answer
722 views

### Qucs model for 2.4 GHz matching circuit

I am designing a matching circuit for an EFR32BG13 SoC. The current board layout looks like this: In addition to the visible layers (top and bottom), layer 2 is a solid ground plane and layer 3 is a ...
1answer
398 views

### Why is there no current flowing through the relay coil in this Qucs 0.0.19 simple dc circuit?

I just started looking at Qucs and am going through the components. I am puzzled by the results shown by the ammeters in the relay circuit below: As you can see from the table, the circuit on the ...
1answer
553 views

### Matching wideband antenna with QUCS

I am trying to match a dipole antenna to a 50Ω source. Problem is that for my frequencies (VHF) the complex impedance basically circles the 50Ω point between VSWR 2 and 3 lines. Because of that ...
1answer
2k views

### Nonlinear equation solvers in SPICE simulators

We have an assignment at the Parallel processing class, the target is to implement a Non-linear Equations solver on cuda based on Newton Raphson method and to interface this solver with an application ...
1answer
575 views

### qucs capacitor simulation

I was playing with qucs and noticed that capacitors are not simulated as I expected. I designed simplest circuit that illustrates that case. AC Source: 2 Hz (2 times a a second) Capacitor: 1pF ...
2answers
284 views

### QUCS Darlington pair

I'm modeling a Darlington pair in QUCS to understand better how to use it in practice. The model is below: The DC analysis predicts a current in the base of T1 of about 1uA and a collector current on ...
2answers
429 views

### QUCS simulation radio transistor amplifier

I'm trying to design a small amplifier for AM signals to use before the usual diode-C-R detection (the reception in my area is very poor). I devised a QUCS simulation as below: The diode and ...
1answer
637 views

### How to setup a simulation on QUCS for a RF differential source?

I need to setup some simulations on QUCS for the RF circuit below: Pin1 is IC's positive port and Pin2 is IC's negative port. My initial goal is to investigate the circuit behavior on different ...
1answer
756 views

### Simulate capacitor discharge in Qucs

I want to find how long a capacitor takes to discharge from 12 volts to 2 volts using Qucs. I can use a voltmeter to measure the voltage across it when it charges up, but I cannot turn the power ...
2answers
2k views

### QUCS simulation of simple capacitor/resistor circuit - strange results.

Hi I have just started to learn electronics. In order to understand the RC constant I have built the following very simple circuit in QUCS simulator. According to the formula RC time constant = R ...
1answer
2k views

### Add a timer LM555C on Qucs

Does anyone know how to add a timer on Qucs ? The component's navigation bar doesn't help at all, It confuses me, I can't find a timer. I wondering, perhaps It could be added through library. In this ...
1answer
516 views

### Qucs How to add 10uF Polarised Capacitor

I'm new to this site. I have a small experiment. I did trying to make a circuit from a schema that needs 10uF Polarised Capacitor in the schema. I use Qucs (Quite Universal Circuit Simulator) qucs....
1answer
2k views

### Coupled Line Filter Design in Qucs

I'm getting to grips with designing coupled line filters and wanted to implement the band-pass filter described in Example 8.7, p. 435 in David Pozar's excellent "Microwave Engineering" just as a ...
1answer
11k views

### How do I import a spice model into QUCS

I am trying to import one of the spice models (from here) into QUCS. I haven't been able to find much documentation about this except for vague hints that it is possible.
1answer
4k views

### How can I create a new component using Qucs?

I'm using Qucs for a simulation, but I don't understand how can I create a new component (E.g. a new LED from a data sheet). How can create it and use it easily in my project?
1answer
1k views

### How to model transistor ATF 53189 in QUCS?

In my internship I have to create an amplifier with low noise, high impedance and that works in the 100 to 400MHz band. While searching for a transistor, I found the ATF 53189 (datasheet), which ...
1answer
767 views

### How do I measure the characteristics of a voltage divider in a QUCS simulation?

How do I measure the characteristics of a voltage divider in QUCS? Below is what I have tried thus far, using Qucs 0.0.15 on Ubuntu 10.04 I want to measure how the voltage at the center of a ...
2answers
1k views

### Is there a way to open/import gschem .sch file in qucs?

Is there a way to open .sch files produced by gschem in qucs? The two applications use different file formats. Does anyone know if a converter exists?
2answers
19k views

### Qucs - what is DC sweep?

I'm learning how to use Qucs using the tutorial. But I have no idea what is DC sweep, AC sweep, parameter sweep, Vsweep, ... and so why to even use them. Could anyone please help explain what are ...