LTSpice parallel LC simulation

Hi Imogen120 ,

I can't help you with the basics of LCs, and hopefully someone from the community can chime in here. Nevertheless, I can tell you by inspection of the image that you have an unconnected net name "N1" (floating in space) and your resistor is not connected to ground, and is floating. Move the ground wire a little lower so the end of it covers the pin of the resistor. When connection is made, the pin will go away. Same thing for the net name. Move it to the junction or wire you want named so that the net name pin disappears.

For future reference, always upload your schematic files; makes debugging much easier for community members.

mike

Hello Imogen, 

here's an answer to some of your questions:

Imogen120 said:

why if i click different parts of the circuit is the frequency response different i.e the left side wire gives green no response but the right side gives the expected resonance frequency

If you click on a node in AC-simulation you see the frequency behaviour of that node voltage. On the left side, the voltage does not depend on frequency, cause you force a voltage of constant amlitude 1V and constant phase 0° with the ideal voltage source V1. So it has to show 0dB and 0° at all frequencies. On the right side you see the frequency behaviour of your LC circuit as it forms a complex voltage divider with R1. 

Imogen120 said:

Also how do i calculate Q

measure the width Δf of the resonance peak with two cursors a calculate Q=f_res/Δf. In your simulation the shape of the resonance seems distorted due to the limited number of data points (100 per decade). The dip will go further down (and Δf will be smaller) if you use e.g. 500 points per decade.

Finally in your simulation Q may be very high, as you simulate most probably with ideal L and ideal C. In real world the parasitics of your components may limit Q. If you know parasitics of your components, you should include them into the simulation, otherwise the simulated Q may not be very meaningfull. 

Imogen120 said:

impedance

as the complete current through L||C flows also through R1, you may plot the ratio of (V(n001)-V(n002))/I(R1)

Imogen120 said:

s11 curve

I think s-parameters make only sense, if you operate (or simulate) your network with some characteristic impedance. (not, if you drive it with an ideal voltage source with impedance 0). 

Imogen120 said:

there seems to be no understandable resources out there for a complete beginner!! 

You may start with a Google search like "LTSpice tutorial beginner"

best regards

Achim