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  1. walid1

    How this ps unit works??

    The circuit in the following figure (from: http://www.hobby-circuits.com/circuits/power-supply/dc-power-supply/891/variable-dc-power-supply) represents a variable power supply Transistor Q1 is npn type This was corrected in the following figure I have thought carefully about this circuit, but...
  2. walid1

    Impedance relation between 2 Bjts

    Hi, If there are two BJT small signal amplifiers (common Emitter) cascade connected using a suitable decoupling cap The first preamp has an o/p imeadance Zo, and the second has an i/p impedance Zin Now we have Zo and Zin and a cap betwwen them My question is: Is the connection series or...
  3. walid1

    27MHz colpitts oscillator qestion

    This circuit was intended as 27MHz colpitts oscillator: and whem simulated using multisim10 sofware I get: I have some questions: Any osci. Needs a FB to sustain oscillations, I think that this FB from collector to base path through the parallel two caps; the internal transistor capacitance...
  4. walid1

    LC and Oscillators

    Hi I noticed in many books that LC tank is connected to the base of the transistor, while connected to the collector in a real designs. Why this confusion? thanks
  5. walid1

    What does the 33uH coil in this circuit?

    sorry there is no respond
  6. walid1

    Why prefer to use the center tap???

    Often observed in many of the schemes that the circuit designer prefers to use the center tap as in Fig.(1) and not, as in Fig.(2), why? Thanks
  7. walid1

    What is the function of this circuit?

    http://www.sentex.ca/~mec1995/circ/at121.html
  8. walid1

    A 1n4148 diode makes the transistor on and off?

    I've built this emergency lighting circuit When the main voltage 230 V is present, LEDs turn off And when does not LEDs turn on Transistor and 1n4148 diode are responsible for making the LEDs turn off Question: How do the 1n4148 diode makes the transistor on and off? Thanks note: the...
  9. walid1

    Brightest White LED

    How do measure the Brightest White LED and see if it is damaged or not? thanks Note: I have tried to test in the same way as the normal LED, but did not give me any reading from both sides
  10. walid1

    Is it bad design?

    What is the function R3 If you know that the output voltage at both ends of the 220u capacitor is 9 volts DC, is not this resistance wastes 9mAh all of time What is the point of that? thanks
  11. walid1

    questio: L-network

    I read in the book: RF Circuit Design, chapter 4 page 66 How can matching 1000 ohm source with 100 ohm load? thanks alot
  12. walid1

    Why caps in paralell?

    the caps at the right, why 10p//15p? what if use one 25p cap? thanks
  13. walid1

    How to distinguish between FM and AM transmitter circuits

    hi please look at the following circuit, the author claim it is AM transmitter: it is from: http://www.zen22142.zen.co.uk/Circuits/rf/amtx.htm it is look exactly FM Transmitter, the only difference is in the values of capacitors and coils!!! Is there another difference I did not watch? Are...
  14. walid1

    LC tank circuit frequency

    Hi when you build a FM transmitter with  LC tank circuit the frequency is: f = 1/(2 pi square root LC) why then when battary goes down the frequency is altered in the receiver? thanks
  15. walid1

    Is it a hartely oscillator??

    Is this circuit using a hartely osc.? if yes please answer these questions: 1- is the emitter resistor affect the frequency of oscillation? 2- this is a transmitter circuit, is it FM or AM and why? thank you very much.
  16. walid1

    question about symetrical swing

    Hi when i want to design a preamplifier using BJT and need to have a maximum symetrical voltage swing at the output, then two conditions must be satisfied: 1- VCE = 0.5 VCC 2- I (saturation) = 2 IC Is there other conditions must be taken into acount?
  17. walid1

    correct me please

    Hello When one design  preamplifier using BJT voltage-divider unbupassed Emitter config, one want max symetrical signal swing at the collector. To do this, VCE = 0.5 VCC & I (saturation) = 2 IC = VCC/(RC+RE) If I want a voltage gain = A, then A= RC/(RE+re), where re = 0.026/IE, so RC =...
  18. walid1

    a cap vlue????

    Hello I built an audio amplifier that has an input impedance of 12k ohm my source signal was 1 mV and internal resistance Rs=1.2K ohm what the suitable value of the  capacitor that must be inserted between? thanks alot.
  19. walid1

    How does this simple circuit operate?

    Hi this is the circuit thanks
  20. walid1

    reshaping a signal

    Hi I need a circuit that  when the upper signal is in, get the out signal at the output thank you   if the phoito is not appear. the input sirnal is a dc positive pulses and the needed output is dc contenuous
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