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  1. A

    Dual Power supply

    Employ a current limit circuit and power your voice circuit before the current limiter.
  2. A

    AM reciever mixer

    I think the text says it all that it is a coupling capacitor to couple back the signal for the circuit to oscillate. You don't need high gain for the oscillator. The total loop gain only need to be >1 to overcome circuit losses and enough phase shift to feed back the signal in-phase. The...
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    AM reciever mixer

    http://www.electronics-tutorials.com/receivers/am-radio-receivers.htm
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    School Project for "Electronics"

    You may find this handy http://www.kpsec.freeuk.com/components/led.htm
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    School Project for "Electronics"

    A led will emit enough light for your purpose (to locate the switch in the dark) at low current levels <5mA or so. Depending which battery you use, it may last for days or weeks. If you want to make the led to flicker that can be done with a simple circuit or use a flickering led from your...
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    precision rectifier

    I am trying to say that very little DC offset on the input will make the peaks uneven. Read your generators instruction manual to find out where is the cal position. Some generators will have a internal adjustment to calibrate the DC offset zero position. That may be out of calibration. More...
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    precision rectifier

    Your function generator may have a dirty/noisy offset pot. You don't need much offset to mess up the result. Have you tried making R3 variable and adjust for balance?
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    Electronic Eavesdropping Devices Detector

    I managed to find a model for the BFR90A. It turns out that it can perform a bit better. More gain overall, but with the previous bias the input match above 1GHz was only -5dB. Running the transistor at 10mA instead of 7mA improved this condition. First plot shows the problem with bias 7mA...
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    Electronic Eavesdropping Devices Detector

    OK, here is the modified input circuit to try. The first picture shows the original circuit and a plot of the gain (blue) and input match (red). It is clear that we have loads of gain (23dB) from near DC. As bugs will normally be in the FM band (88-108MHz) and up, we don't want this gain at the...
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    Electronic Eavesdropping Devices Detector

    The circuit need a much better high pass filter on the input, to eliminate the low frequency noise that is triggering your circuit. The RC filter is not enough. Another way will be to have a switchable filter for commercial FM band, mobile etc. The circuit also need to me in a metal or screened...
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    precision rectifier

    Yes I have seen a few variations on this circuit function!
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    precision rectifier

    I tested his circuit as well. Worked well after R3 was adjusted for balance.
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    precision rectifier

    I constructed his circuit and made R3 variable and obtained good results. I also modified the circuit as shown and waveforms looked good up to 1kHz+ Results agreed very much with the simulations.
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    precision rectifier

    I think that his problem is due to resistor tolerances. Doing the math on his circuit shows that using 1% resistors the peaks can differ by as much as 10% One of the resistances (R3) should be made variable to adjust for proper balance. Using 5% resistors, peaks can differ by 50%
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    precision rectifier

    Start a process of fault finding. You can't just rely on the calculations. Check circuit connections. Increase  the resistance values to see any improvement. Change the opamp or use another type. Make sure your AC signal you feeding in does not have any DC offset. This will cause what you are...
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    precision rectifier

    His 5V p-p signal should not cause any problems at this minimum current spec.
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    precision rectifier

    Simulation also show no obvious problems using the part values in his diagram.
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    precision rectifier

    Should work. Re-check all your wiring for a possible mistake
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    Electronic Eavesdropping Devices Detector

    Many cheap bugging devices work in the commercial FM band so that may cause problems detecting them out of all the other stations.
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    LED Display digital clock project

    The circuit have different clock settings for fast and ultra fast setting as well. There is one setting for normal run mode that uses the 1Hz output. For calibrating the crystal frequency a frequency counter will be handy. The 4040 is just dividers. You don't need to have all the settings...
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