Very wide band oscillator frequency limits.

[Lightium]

Are you saying the H of a pin bulb would be larger, then a few turns on a screw driver or a tooth pick?

 

[Nigel Goodwin]

Then why try and use a bulb?, which is far larger than winding a few turns of wire?.

You never mentioned a pin bulb?

incandescent light bulb from a pen light for the inductor

But if you want a smaller coil, you just wind it smaller with thinner wire.

 

[Tony Stewart]

I just hadn't considered the Q. I guess I'll have too, I am trying to make some very small tank circuits.

Define f, Q and "very small" Generally like Xtals it is wiser to use series resonance for VHF or > 30 MHz due to the sensitivity of stray capacitance in parallel loops. Using an "RLC monograph" is an intuitive and quick way to do many tank circuit designs without a calculator. Parallel Q is the R ratio above the intersection of LC&f. While series Q is the R ratio below that impedance.

Another tool is free "Saturn PCB Design" windows app on the planar Inductor tab> circular.

 

[Lightium]

I have an lcr meter with a Q function.

 

[Tony Stewart]

The LCR meter needs to read 0 nH when shorted and xx nH with connected to coil. at max f.

10 nH is about 15 mm of straight wire and so you cannot do this on a breadboard. The collector should not have any significant inductance, meaning a couple of mm SMD Rc resistor to an SMD decoupling cap between Vcc and gnd. This would shift the phase of the oscillation, reduce the gain and probably stop oscillating.

https://tinyurl.com/2evmw88f

This is just a quick and dirty simulation, and not optimized , hFE= 30

 

[Tony Stewart]

Although I still don't know how small you can make a tank on a copper board but here is 1.389 GHz
This demands a better configuration for higher f's.

https://tinyurl.com/2evahup3

 

[Tony Stewart]

If you want the best book on filter theory, https://ia803101.us.archive.org/20/items/HandbookOfFilterSynthesis/Handbook of Filter Synthesis.pdf which compares LC coaxial and waveguide filters around p22

 

[Lightium]

That's all very good information, I appreciate it.

 

[Jverive]

I'd guess that it is not R2 directly, but changing the biasing changes the voltages on the transistor junctions and causing a "varicap" type effect.
(It's a seriously weird circuit!)

The circuit is basically a two-transistor Schmitt Trigger circuit with a resonant LC tank as load for the first transistor, but I guess it looks weird because not too many people build Schmitt Triggers from discrete components anymore.

 

[Tony Stewart]

Yes forget that cct but useful in CMOS.

The circuit is basically a two-transistor Schmitt Trigger circuit with a resonant LC tank as load for the first transistor, but I guess it looks weird because not too many people build Schmitt Triggers from discrete components anymore.

I agreed https://www.electro-tech-online.com...cillator-frequency-limits.164622/post-1434578