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  1. 321Mark

    Op_Amp_Booster_Circuit

    Ok, I'll check for the compensating capacitor. There is not one in the system. Yes it is a circular inductosyn and the length of the cable is over 20 feet and its flex cable where one conductor is over top of the other. We measured these two conductors with no source or load connected and are...
  2. 321Mark

    Op_Amp_Booster_Circuit

    I think there is a cable drive issue associated with the circuit. The output drives a long flex cable and I suspect there may be a fair amount of capacitance in the cable. I'm going to try and measure the capacitance. The output looks OK when its not driving the cable, but distorted when its...
  3. 321Mark

    Op_Amp_Booster_Circuit

    This circuit was designed for us for an Inductosyn system. It drives a high level sine wave (10v) to the "primary" coil. The signal looks ok on the scope, but on the analyzer it's showing distortion products. The drive frequency is 20KHz. This circuit has enough drive, but I was looking to get...
  4. 321Mark

    Op_Amp_Booster_Circuit

    I'm trouble shooting a circuit for an R/D converter. One circuit is an op-amp booster. It takes a sine wave in differentially and drives it single-ended. It uses a booster stage to drive the signal at 10V peak. I'm not familiar with booster circuits using transistors. Can anyone tell me if...
  5. 321Mark

    Transistor Switch

    I've heard of a method for selecting the shunt resistor. I had something to do with the leakage current of the transistor. Anyone have any information on this?
  6. 321Mark

    Transistor Switch

    Is there a way to calculate the ideal resistances required to properly design a simple transistor switch? Let's take an NPN low side switch with the emitter grounded. The circuit has an input resistor (Rin) from an external input and a resistor from the base to ground (Rb) to hold the...
  7. 321Mark

    Dead Band Circuit

    First of all, thanks for the help on the AGC circuit post. The problems I was having were in the RF path, not the AGC path. Circuit works fine except... I need a dead band circuit. I want to ignore the output of the detector until it gets to about 0.5 volts, then bring the ACG into play...
  8. 321Mark

    ACG Control Loop Help

    OK, I made some progress. One problem - as I would bring the RF level up on the AGC amp a point would be reached where I thought the AGC circuit was oscillating. Turns out that something between the AGC amp and detector module was causing the problem. Operating open loop, (no AGC)I would see...
  9. 321Mark

    ACG Control Loop Help

    Yes, pulses come out of the loop with a fixed AGC level. I think I have created a fast oscillator. Its definitely negative feedback - the detector is on the (-) input and my reference level (DC) in on the (+) input. Even though the loop is oscillating it controls the RF output and I can...
  10. 321Mark

    ACG Control Loop Help

    Thanks for your help so far... When you explained to..."Then tune feed back resistor (capacitor shorted) for fast and well damped response" Should I do this by switching the RF ON and OFF in a step-like manner and monitor the control voltage until I get a good response? Also, is the...
  11. 321Mark

    ACG Control Loop Help

    Text should read: I fed the detector output through a 47k resistor into the (-) input of an op-amp configured as an error integrator with a resistor and capacitor in series in the feedback loop (single pole, single zero). On the (+) input of the op-amp integrator I connected a reference...
  12. 321Mark

    ACG Control Loop Help

    Sorry, I have a 47K input resistor. This sets the low frequency gain and then you see the slope of the integrator. Works as described previously and oscillates with the triangular waveform. Mark
  13. 321Mark

    ACG Control Loop Help

    This is my first time designing an AGC amp for an RF application. I'm using a commercial AGC amplifier and detector (Teledyne Cougar). The AGC amp has a 0-5V control signal, 0V is full gain. The detector has a 0-5 volt output. 0 volts occurs at -40dBm and 5 volts at +10 dBm. I want the output...

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