simple radio not working

[xchip]

Hi guys.

I put together a LC tank tunned to a freq of 77.5Khz, then I connected it to an op amp and then to my oscilloscope. I was expecting to see some oscillations at the output, after all the antenna should bring some 'white' noise to the LC and the LC should just resonate at its resonance freq. I was expecting to see a nice wave in my oscilloscope but its all flat.

[See pic for circuit] (edit: NOTE that the pic has wrong values for the LC resonator but the rest is OK)

I bet something in fundamentally wrong in my design... Any ideas on what is wrong?

[wraper]

...50Hz resonance frequency of lc circuit.

[Circlotron]

Yep, cap and inductor values are way to large.
Also, make the opamp cct non-inverting rather than inverting like it is now. The input impedance is only 1k and this will damp any resonance of the tuned cct. Non-inverting is much higher impedance.

[xchip]

Yep, forgive em for the 50hz LC I forgot to update the circuit with proper values.

I never thought an inverting op amp would have a low impedance(which now that you said it loos pretty obvious)

I'll give it a go and will post my results. I'm pretty excited

[ElectroIrradiator]

Depending on what you are trying to do, then building a gyrator receiver may be the better way to a DCF77 receiver.

If you are just looking for an excuse to learn about LC circuits and basic radio techniques, then please disregard this comment.

[xchip]

eheh, yes this is just an excuse to learn something about LC circuits, but I do appreciate your pdf, I will build it as soon as I get the LC thing working! thanks!


Another question though. I am using a virtual ground at 2.5 volts, I presume that LC circuits wont like that and prefer to resonate around 0V. I guess I have to put decoupling caps, where would you place the caps?

[xchip]

Got it, there is my resonator amplified by an op amp, I used a non inverting configuration so the high input impedance of the op amp doesn't damp the oscillation as Circlotron suggested


I have a DDS 9850 doing a freq sweep and I'm getting a nice spike at 54.9Khz

Thanks to everyone, I am so happy!