RLC receiver v. Quad Op-Amps!

[GODELisMYdad]

I've been working on a receiver design, quad op-amps with independently settable central frequency, gain, Q... and I've not been able to get it to function properly at 1.6 MHz. It seems to be fine at 1.0 MHz though anything higher than that results in oscillation in the circuit. I've been told op-amps aren't particularly sought after because of problems at higher frequencies, so we've now moved on to an RLC design with a variable capacitor that will sweep through the range of frequencies from 1.2 MHz up to 2.0 MHz.

What are some of the problems I can expect with the simpler design. And any tips or forewarning will be greatly appreciated.

 

[Nigel Goodwin]

You don't make radios with opamps - try looking how radios are designed.

 

[GODELisMYdad]

Good thing I'm not making a radio.
The receiver is going to detect reflections off plasma. The original plan had the opamps as filters/inverters for the receiver to get the stray noise out.(High Pass/Low Pass)

 

[Nigel Goodwin]

Good thing I'm not making a radio.
The receiver is going to detect reflections off plasma. The original plan had the opamps as filters/inverters for the receiver to get the stray noise out.(High Pass/Low Pass)

Perhaps try been more explicit?, but it still sounds like you trying to receive radio frequency signals - which means a radio.

Do you perhaps mean detecting radio emissions off a Plasma TV? - we can only guess while you're been vague.

 

[MikeMl]

There are opamps that will work at your frequency of interest. What opamps are you using? You may need to use a single opamp per package, and put some interstate shielding.

 

[GODELisMYdad]

We originally thought the opamp slew rate was too low, but the ones we have now are for over 200+volts, so we know that's not it. And the original design did have the four opamps in the same housing, which we now have as seperate packages.

Although with both of these we still don't have it behaving as it does in the designs. We also thought interference from maybe the leads, or capacitance in the circuit, but we've all but eliminated those with it now.

One idea was that the circuit was feeding too much on it's own gain, so we decreased the circuit from unity gain, down to .5 gain. However, now we're not getting any discernible output.

 

[MikeMl]

Can you post your circuit?