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1 Mhz Amplifier circuit

  1. Mar 24, 2013 #1
    Hi, I am a inventor and Electronics Tech. I am creating a 1 Mhz Amp for my own invention, and it will be enclosed in a Faraday cage so there is no emissions to worry about. I have been reading Fundamentals of Engineering Electromagnetics, and was wondering about the difference in the source voltage on the amp circuit and how the electrical charge affects the inductor and how that would change the operating inductance of the amplifier circuit. I plan on creating a 80 watt or 100 watt peak output power of a 1 mhz signal.

    I am thinking of using a 200 volt source voltage.

    can I just use the standard frequency calculator of 1 over 2 pi square root of L and C ? what adjustment is done for the voltage that is applied to the inductor in a tuned tank circuit.

    on the emitter and base of the amplifier, would I use two types of RC filtering circuits, a lower band and higher band frequency?
  2. jcsd
  3. Mar 25, 2013 #2


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    without a schematic, i dunno how to begin to respond to your question. i dunno why, unless you want it tuned to 1 MHz, there need to be an L in there at all. 1 MHz ain't all that high in frequency. your amplifier need not have plumbing in it, like if it were microwave.

    your cage better be good. 1 MHz is smack dab in the middle of the AM broadcast band. the FCC might come out there and kick your butt if your signal leaks out.
  4. Mar 26, 2013 #3
    skin effect

    Actually the Skin Effect which occurs at high frequencies or higher do not penetrate a metal surface very much. so a faraday cage is easily constructed. Now take a standard npn common emitter amplifier circuit to amplify the 1 mhz, my real question, I use a tuned tank circuit on the collector to 1mhz, the question is how does the voltage across the inductor change the inductance in the tank circuit.
  5. Mar 26, 2013 #4


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    Since you are an inventor, I'd expect you would look a all the "prior art" for 1 MHZ oscillators and RF power amplifiers before you try to "re-invent the wheel". Ls and Cs change with temperature, are bulky, difficult to tune to exact desired frequency, and contribute to frequency instability.

    Typically 1 MHZ oscillators use a crystal as a frequency reference, and not tuned tank circuits. Once the crystal oscillator is functioning, an RF power amplifier is typically fed by the oscillator. Source voltage of the amplifier does not determine the power output.

    This thread may be locked by the monitors/mentors because our rules don't allow us to discuss dangerous projects. A 100 Watt RF power amplifier CAN BE DANGEROUS TO HUMAN HEALTH. I suggest you consider a comptent engineering consultant to validate your plans BEFORE you apply power inisde the "Faraday cage".

  6. Mar 26, 2013 #5
    I am not inventing a 1 mhz amplifier, its just part of the circuitry involved, i was in the Navy and Maintained 1500 watt RF Radio's, but for simplicity sake, I will forgo the 100 watt question. The Source voltage P = E^2/R I believe is the formula for wattage; and my original question about Electrical Engineering was the question about how Voltage applied to a Inductor can change the inductance value called henrie's used in a tuned circuit? Not asking about really dangerous stuff here.

    If the rate of change of current in a circuit is one ampere per second and the resulting electromotive force is one volt, then the inductance of the circuit is one henry. and V (volts) x s (secs) / A amps.

    now inductance = magnetic flux / current . and magnetic flux depends on the voltage applied and stored in a inductor.

    okay still asking the question, how does voltage applied to the inductor affect the inductance of the inductor.
  7. Mar 26, 2013 #6
    If your inductor is linear it doesn't.

    There will be a tiny variation in inductance due to mutual inductance between unit lengths of your inductor (eddy currents) but it is a second-order effect. For your 1 MHz amplifier you can take the inductance as a constant.
  8. Mar 26, 2013 #7
    thanks for the answer, I did read about inductors again in the engineering book, and now why understand why its treated as a ratio; linear affects are usually expressed in straightforward ratio's because of your answer given to me and why there's not much information about the differences in applied voltages, and eddy currents and those affects. thanks much.....John
  9. Mar 27, 2013 #8
    Perhaps your experience with inductors, particularly around 1 MHz, was with inductors that used powdered iron or ferrite cores. At some point the CURRENT, not voltage, will cause those cores to saturate resulting in a change of inductance. For that reason powdered iron and ferrite cores are not used in higher powered RF circuits.
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