Clapp Oscillator with Filter

[Havass]

Hello,

I have designed a Clapp oscillator with help from others. But now I do not know how exactly this circuit works because the filter is integrated in the LC-oscillator. I dont know what R5 and L2 do and also C10,C11 and R7 work. Normally C11 and R7 would be a CR lowpass-Filter, but C10 is confusing me.
I would be very glad if you could help me

[MathWizard]

Why is R6 shorted, and in real life, if those polarized caps' were upside down, they might explode.

IDK near enough about this, I'd put R5 and L2, in parallel with L3,C9...that part, and then try to find the poles and zero's of just that part alone, to try and see what LCR values matter the most. IDK how much the poles and zeros of that section would matter, in the full circuit.

Maybe you know all this, but R5 would be setting the DC bias voltage, and will get rolled into the AC gain also. Is there coupling between the inductors L2 and 3 ? That's way over the frequencies I should be talking about.

[Kim Christensen]

Hint: Oscillators are amplifiers with positive feedback. So think about the phase shift from the amplifier's input to it's output and then realize that the resonant feedback circuit must shift the phase so it becomes positive feedback.

[RFDx]

I dont know what R5 and L2 do and also C10,C11 and R7 work. Normally C11 and R7 would be a CR lowpass-Filter, but C10 is confusing me.

The capacitor in the series resonant tank circuit was split into C9 and C10. C10 is a low impedance tap point that extracts an output voltage with low harmonic content for the 50 Ohm load. The 50 Ohm load (R7 or R8, there is only one load) is coupled lightly to the tap point through another, small capacitor (C11). C10 and C11 determine how much power is available at the 50 Ohm load. The goal was ~0dBm/1mW in the original design.
R6 is shorted out btw.

[Havass]

The capacitor in the series resonant tank circuit was split into C9 and C10. C10 is a low impedance tap point that extracts an output voltage with low harmonic content for the 50 Ohm load. The 50 Ohm load (R7 or R8, there is only one load) is coupled lightly to the tap point through another, small capacitor (C11). C10 and C11 determine how much power is available at the 50 Ohm load. The goal was ~0dBm/1mW in the original design.
R6 is shorted out btw.

Thank you, now I understand what C9 and C10 are doing and Ive corrected the short at R6. . R8 is just a load from Harmonic Balance of Keysight ADS. But what exactly are R5 and L2 doing? And are C11 and R7 no Highpass-Filter?

[RFDx]

R8 is just a load from Harmonic Balance of Keysight ADS. But what exactly are R5 and L2 doing? And are C11 and R7 no Highpass-Filter?

There is no need for R7 if R8 is the load (output port) in ADS. R5 and L2 transforms the (low impedance) voltage source into a high impedance current source, at least for AC signals. For DC it's only 100 Ohms. R5 + L2 are "invisible" to the actual oscillator circuit. Yes, C11 and the load R8 (or R7) form a high-pass filter but their purpose is not really to filter.

[wasedadoc]

Normally C11 and R7 would be a CR lowpass-Filter

High pass, not low pass.