Search results

Search Forums New Posts
  1. walid1

    Voltage control oscillator VCO

    yes Mr Alun i want to calculate LC but the problem is in C itself. Is Ceq = (15p in series with 3.9p) // (varactor capacitance) OR Ceq = the three elements in parallel. THIS IS MY QUESTION. NOTE: Alun, your answers always talk about basic electronics, may be my questions not clear but please...
  2. walid1

    MIC coupling capacitor

    Hi Audioguru You said: "It is difficult to calculate the gain and input impedance of the mic preamp you posted because it has negative feedback applied to its input. The transistor has an input impedance of about 2k ohms and the negative feedback  of about 2k ohms is in parallel with it." (1)...
  3. walid1

    A chock coil

    Hi audioguru and Staigen How you think calculate this value, this what i need to know gesign gesign gesign gesign gesign gesign gesign gesign gesign
  4. walid1

    Dots in transformer symbols

    To Alun, if they in phase or not where to put the dots
  5. walid1

    10kHz FM modulation

    thank you Alun it is good answer
  6. walid1

    MIC coupling capacitor

    it is very good answer audioguru but still one point : 10uF is not so big value and can be used instead of 100 n is this true? And how you choose this cap in your FM Tx thanks
  7. walid1

    Voltage control oscillator VCO

    Alun please reread my question carefully before you trying answer. OK i am weak in ENGLISH but i think my question is obvious. thank you walid
  8. walid1

    Air coils winding

    Thank you alun you don't understand me what i mean is if i want 100nh air coil and wound it in different way but the same value, is this ok or not thanks
  9. walid1

    IR photodiode

    This is a diode operate on Infrared light emitted from an IR diode, the question is: What happen when IR ray strike this diode? Is it become sort circuit? Are there any differences if we connect it in reverse, that is kathode inplace on anode and vise versa. THANKS
  10. walid1

    A chock coil

    In many FM Txs they use a coil connected from the o/p of a high frequency stage to the power supply, this coil is of fairly larg value (for example 100uH). The purose of using such coils is to chock (prevent) high frequency sigals from going to other stage through the power supply. For example...
  11. walid1

    Antenna

    Any transmitter is connected to the antenna through some length of wire. If the frequency is high say 100MHz i think that the waves will radiat out of this conncter. What we must do to prevent this radiation.
  12. walid1

    100 uH coil

    how can i wound 100 uH coil
  13. walid1

    Voltage control oscillator VCO

    VCO used frequently in FM transmitter for modulation. In Fig.VCO shown below I cut the VCO section from a FM transmitter (http://hem.passagen.se/communication/bug_rf.html) for discussion. VCO start from BB149A and end at the emitter of T1. BB149A, 3.9 pF, 15 pF and L1 make LC circuit with C...
  14. walid1

    The capacitance of the varicap

    The varicap is a special diode that which changes its capacity according to DC voltage applied to it in reverse manner, that is when high DC => low capacitance and vice versa, I think this is OK. Now, looking to Fig.varicap (FROM: http://hem.passagen.se/communication/bug_rf.html), the varicap...
  15. walid1

    MIC coupling capacitor

    In Fig.MIC cap (part of FM Tx from http://hem.passagen.se/communication/bug_rf.html) below you can see the MIC connected to 100nF cap. I Know that 100nF value is not critical and I may use say 10uF, but to what level this value is not critical? What happen if i use a 4700uF or 1pF, please...
  16. walid1

    Air coils winding

    in many circuits there is an air coil, they told you that it is say 0.1 uH and also told you number of turns you must made and the former diameter and if this close wound or loose. If i try different values to achieve the same 0.1 uH using some formula, is then this coil operate ok as the...
  17. walid1

    50 ohm antenna

    i read this frequently, how I know that this antenna is 50 ohm, or how i can made a 50 ohm antenna, what the theory behind this. If it is a transmitter antenna and the transmitter operate at 50 MHz Fm what is the optimum length of this antenna to be 50 ohm. What the length if the freq. = 100...
  18. walid1

    10kHz FM modulation

    When I read this statement I understood that if the carrier signal is say 100MHz it will be shifted to 100.01 MHz up and 99.99 MHz down, is this true? Thanks.
  19. walid1

    Dots in transformer symbols

    i see often dots in transformer symbols, how these dots. How can I determine these dots practically on a real transformer. Thanks Walid.
  20. walid1

    Wireless telephones

    just plain cordless phones, i have one i need to repair it or at least understand its different circuits.
Top