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  1. walid1

    what is unipolar pam

    Read this pdf file I hope it will help u: www.comlab.hut.fi/opetus/245/2004/07_digibaseb.ppt
  2. walid1

    problem in PAS system

    I suggest to carfully read the LM386 datasheet
  3. walid1

    need help urgently

    Please take a look at this site: http://web.mit.edu/2.151/www/Handouts/FirstSecondOrder.pdf
  4. walid1

    methods of adjusting the camera iris and black

    What u exactly mean?
  5. walid1

    Question about Ground Loops

    I read the following from the link above: A ground loop in the power or video signal occurs when some components in the same system are receiving its power from a different ground than other components, or the ground potential between two pieces of equipment is not identical. my questions are...
  6. walid1

    design guieds for Forward switching off-line converes

    Hi SupeR-NovA , thank u this is good doing walid
  7. walid1

    -48Vdc on telephones

    you can go to this link it is a rich text about telephones http://www.epanorama.net/links/telephone.html I hope this may help you
  8. walid1

    Universal battery charger

    audioguru: "Without it then when the battery voltage reaches the threshold voltage, the circuit might oscillate." Walid: (1) What the threshold voltage if the charged batt is, say, 9v           (2) is this op-amp oprate as a comparator. I never see a comparator with a feedback resistor.
  9. walid1

    Universal battery charger

    audioguru: "The actual value doesn't matter. It filters noise from the battery if it is loose in the connector and provides a small delay." Walid: it is good news that the cap value (4.7u) doesn't matter, but still i can't understand u, please explain it more for me, thanks.
  10. walid1

    Universal battery charger

    In the circuit shown below there is a Universal battery charger from: http://hem.spray.se/lythall/power/charger.htm it is easy to understand and to implement, but i have some questions: (1) Why u think the designer use the 4u7 cap. (2) If LM358 is used as a comparator, why:       (a) using...
  11. walid1

    Oscillator drift

    Hi Alun If this is a VCO used in a FM  Tx transmitt at 100MHz, the tank circuit contains these C and L, tell me an example of their values. thank you.
  12. walid1

    Audioguru FM Tx

    Hi audioguru once u told me in one of your replies that u geuss VE to be 2.25V and ... From that deduce your design decisions which are: IC=10mA VE=2.25V Vcc=5V Q2 = 2N3904 has hfe=230 at the operating current (IC) .... If I use these decesions with the same 2n3904, then I measure IC and IB and...
  13. walid1

    Audioguru FM Tx

    Hi Audioguru THE VCO STAGE TANK CIRCUIT (LC) L=100nH, C=5-35pF, so the freq range from 87MHz at c=35P to 225MHz at 5p. To make the coil of 100nH, u may wound 5.5 turns of 1mm enameled copper wire on 5mm in dia former, the turns must be close so that the length of the coil = 5-6 mm. When I...
  14. walid1

    Oscillator drift

    Why you may don't hear about FM Tx osc. your answer is bad, but thank u
  15. walid1

    Audioguru FM Tx

    Hi I put C4 = 50nF instesd of 100nF in the Pspice commands that follows, to see how this affect on the pre-emphasis: Audioguru FM Tx 1st stage (Audio preamp), V- divider configuration Ver.02 VCC 1 0 5V Vmic 8 0 AC 1 *Vmic 8 0 SIN( 0 5M 1K 0 0 0 ) Rmic 8 7 3.3K R2 1 2 150K R3 2 0 39K Q1 3 2 4...
  16. walid1

    Audioguru FM Tx

    Hi audioguru (1) In my calculations above hie= 10.9Kohm at Ic=0.3mA, and Fig 4 above reveal this it is about 10Kohm, so I can say that my calcuklations are true. what would u say? (2) I have the same datasheets from FAIRCHILD. If u look at Fig.2 above u may notice that VBE at IC=0.3mA = 0.63V...
  17. walid1

    Audioguru FM Tx

    Good night Audioguru, U said: You have used hFE (DC gain) of 230 in your calculation for Zin         instead of Hfe (AC gain) of 100 so the actual impedance is less. walid: Why to use AC hfe, u never said that before?              And how to find this AC hfe? And u said: Since the...
  18. walid1

    Audioguru FM Tx

    Hi audioguru, u said: The pre-emphasis at 15kHz in North America is about 7.2 times the         gain at lower frequencies.With its lower frequencies gain of about         18 then the max gain of the transistor of about 130 results in a         pre-emphasis which just makes it and sounds...
  19. walid1

    Audioguru FM Tx

    Hi audioguru; you said: My Mod-3 version of the circuit had an extra RE to raise VE so           that different Vbe in different transistors wouldn't affect the           VC too much. The question: Are u mean a bypassed RE added in series to a not bypassed RE? you said: But I didn't have...
  20. walid1

    Audioguru FM Tx

    audioguru: "I didn't have 320k for R2 nor 60k for R3 so the divider current             to base current ratio is 20:1 instead of 10:1 which better             controls the effect of different current gain in different             transistors." walid: who said that u use R2=320k and R3=60k...
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