Underdamped sine wave generator with thyristors

[iraquois]

I am trying to design a circuit to generate underdamped sine wave (actually it is a basic lc tank with switching pulse. I tried to switch a simple RLC circuit with mosfet switch, but Unfortunately I got so much distortions.).
I have a circuit which people say that it was working once . So I tried to simulate it but it is not working in simulation.
Problems I got:

1) Even if I increase V3 to 100V, Underdamped sine wave starts from 15V.
2) And a big problem is that I see this wave even If I don't send pulse from V2. (Breakdown voltage of SCR is 600V)

I am not sure if this is the proper way for this purpose. If someone has any idea about this circuit or another circuit idea please share. Thank you for reading.

[iraquois]

Actually this circuit is working I tried this. But I see some distortions. So I decided to try another way. It was just replacing "thyristor and diode" with a relay. So finally I could let L and C create damped sine wave. But with this method I got weird results. Or is it possible that I did something wrong? Tomorrow I will try it again.

But in case that it won't work, can you suggest me another way if you know? Maybe I can try it with an optocoupler?
Or should I completely change the topology

[iraquois]

With the schematic I shared before it is possible to acheive 1kHz - 1MHz damped sine wave with damping factor of 15. But right now, I think the hardest one, I am trying to generate 90MHz damped sine wave with Q factor of 15 (means between first peak and the cycle which is %50 of first peak, there should be 3 cycle at least) . I tried this with 25nH inductor and 125pF capacitor. Damping factor seems okey. But problem is, as you can see in the oscilloscope screen, first peak occurs after 3 cycles. Now I think possible explanation is that; Since my capacitor and inductor is very low, even my layout and inductance of the relay can effect the result (also inductance of my capacitor and capacitance of my inductor).

What kind of relay, inductor and capacitor should I use. Should I use handmade capacitor and inductor ? And for the relay since they have at least 10 - 20nH inductance is it possible to use manual switch? for example directly make capacitor and inductor touch together manually.

[Berni]

At these speeds physical circuit construction is more important than the schematic. Even the way you tap off or probe the signal might affect its shape.

If i had to do this i would mostly likely build that single transistor Jim Williams picosecond pulse circuit and run that into a tight compact LC circuit.