Search results

  1. walid1

    Oscillator drift

    I read in a pdf file what appears in fig.oscillator drift below. as you see there is 6 points to take into account to make the osc. stable, I'll concentrate on the first one labled (a); the c/L ratio. what I want is to explain it numerically for FM 100MHz. thanks.
  2. walid1

    PNP and NPN replacements

    I an not so familiar with PNP type transistor. when I see a PNP tran. in any circuit like one that shown below that using a PNP, I immediately think to replace - at least in mind- with NPN. If I want to do so I must invert the power supply. is this what must to do or there are many other things...
  3. walid1

    Mains OFF senseing

    I need a circuit that composed from a 220 to say 12 volts transformer then I rectify this to DC and then connectes to some transistor citcuit. this transistor citcuit must sense the existing or not of the 220vAC. if there is no 220volts the circuit o/p is high and vice versa. thank you for your...
  4. walid1

    Zener diode threshold voltage

    If I have 6.8V 0.5W zener diode, what the minimum value of the applied voltage to make it ON. thanks.
  5. walid1

    12 volt battery charger

    Hi all The circuit shown below represent a 12 volt battery charger from "Sam Electronic Circuits" and I have some questions about it: (1) I noticed in this circuit and all charger circuits that they omit the smoothing cap after the rectifier, why? (2) Q1= BTY79 or similar 6A SCR and Q2= C106D ...
  6. walid1

    Transformerless power supply discussion!

    In the figure below you can see a transformerless power supply circuit, the component values are as follows: R1 = 220K
  7. walid1

    switching diode

    I read this:"a small signal diode of the 1N914 type commonly used in switching applications". I know thast 1N914 like 1n4148 is a small signal diode but what are the switching applications, give me some example on how to use diodes to switch between ON and OFF thanks
  8. walid1

    Diodes as frequency multiplying devices in rf circuits

    I read this statement somewhere in the web, can you please explain this with practical example circuit. thanks very much.
  9. walid1

    What this circuit do???

    Hi all This circuit shown below consists of 6 inverters (NOT gates), that is using the 6 gates in 4069 IC, these gates are connected as shown with 5 resistors, 3 caps and one diode the o/p is as shown. can you please tell me what is this o/p. I think it is an oscillator, but it is very complex...
  10. walid1

    Photodiode terminals

    If I have a photodiode on my table, how can i identify its cathode and anode using didital multimeter? tanks.
  11. walid1

    crystals in series or parallel

    In some circuits I see four 20MHz crystals in series or sometimes in parallel! What's equivalant value then?
  12. walid1

    What are these abbreviatives mean

    What are these abbreviatives mean: QRP QSO NFB circuit thanks
  13. walid1

    Differences between MC3361 & MC3371

    Is there any difference between MC3361 & MC3371, and can one of these be used in place of other, thanks
  14. walid1

    Jr.Member

    What the meaning of Jr, thanks
  15. walid1

    picture under my name

    hi all, i want to put a picture under my name as you do but i don't know how! Please tell me.
  16. 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
  17. 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...
  18. 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.
  19. walid1

    100 uH coil

    how can i wound 100 uH coil
  20. 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...
Top