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Posts posted by walid

  1. hi audioguru

    i can not discribe exactly what going with me but i'll try hope that u understand me
    1) when i tune it to some freq i noticed that it be in a wide region that is it cover from 97 to 102 MHz, strong at the center and gradually weak to other sides

    2) the recieved sound is 80% hum (very strong hum) and about 20% voice, my son talking hallow hallow and i heared him as some thing (rag) inside his mouth, anyone cann't accept this voice

    3)when i take the receiver away and walk i can hear that voices only 80-100 meter

    4) the Tx very senseitive to any touch or any body near to it

    5) when i disconnect C3 i hear pure voice like that when mic faced an amp speaker
    I use 220n//100nF as 330n =C3

    I wait your help hoping this Tx work to use it in my walky talky

    thank u guru very much

    i want to tell u that we have electrical power only 7 hours a day since 2 monthes this is one of the reasons that make my job very slowly because ISREAL destroying the main generators which supply all GAZA strip
    I respect everyone in this world and cann't hate anyone but tell you only to know as a good friend for me, yours

  2. Hi

    I do what guru told me, isolate the amp circuit and remove C4, then
    measure voltages at points mentioned at the above figure and i had
    the following results:
    Vcc 4.96v
    VB 0.74v
    VC 2.43v
    VE 0.12v
    AT MIC 3.14V not 2v as guru

    when connecting my 10 watt amp and talking near the MIC i hear my
    voice clear and strong .........

    now i'll going to connect this first stage to the entire FM Tx to see
    what will happen


  3. Hi Jean-Noel

    Welcome to our forum

    10 years ago when the electricity company suplied us only 170vac instead of 220, i had a step up transformer. One day it burned and emitt abig amount of smoke

    i decide to rewound it and simply did the following:
    got a paper and a pen to write notices
    open its cover and take a long look
    disconnect all connections and make any sign to help u in the reconstruct process
    unwound the wire noticing the direction of wound and the number of turns
    take it to shop and ask him the same wieght and diameter

    when i wound it by hand and because i was harry the turns were not side to side so it take more size than it must, so i reduce the number of turns by about 10% for each step

    finally it work and i had a very good results and i believed from that time that there is no critical

    Now I ask you to share with us your formulas

  4. The circuit shown below is from: http://www.redcircuits.com/Page86.htm

    For me, it is easy to analys any circuit containing npn transistors, but i'm confused when come face to face with pnp type

    i read this in the same page:

    Circuit operation:

    The circuit is inserted between the supply and the load, therefore, until a trickle-charging current of at least 100µA is flowing towards the load, D1 and D2 will conduct. The forward voltage drop (about 1V) available across the Diodes, drives Q2 into conduction and, consequently, Q1 will be cut-off.
    If no appreciable load is connected across the circuit's output, Q2 will become cut-off, Q1 will conduct and the Piezo-sounder will beep.

    Assume that I insert this circuit between a 13.7v charger and a small 12v battery, can anyone explain what will happen at first and when the batt is fully charged.



  5. Hi

    In fact i use An ordinary 7805 regulator with a table power supply adjusted to 9v.
    when i build it the first time on [a special board for experiment that with holes] i noticed some big short circuit, but after solving this problem and assuming that all was OK smell and touch all parts for heat .... i begin to talk near the mic but nothing

    During the tunning process on the FM radio receiver I hear a strong noise in more than 3 places, but near 100MHz was the big noise related to the transmitter

    I then assume that the problem is before the oscillator, mic or the 1st amplifier
    i change some parts and check the connections, but still no voice recieved

    I have a 10 watt amplifier, i want to disconnect the FM Tx from the Q1 o/p and connect this point to my 10 watt amp to check if these stages are ok

    .................. i do this but no voice out of the speaker

    advice me


  6. Hi all my friends, and special HIIIIIIIIIIIII to audioguru

    Now and finally i am going to build this FM Tx , yesterday i put all the components on the table and today afternoon i'll put them together
    my question is if i build my own receiver using TDA7000 or TDA7088 to receive signals from that TX ...
    another way, I want to talk with my friend 100 meter far away, i need 2 units each contain TX and Rx
    If I tune Tx1 to 100MHz and Rx1 to say 80MHz, so, Tx2 to 80MHz and Rx2 to 100MHz
    I know that to each fundamental freq there are some harmonics,
    when, some day i build my first transmitter i hear myself in many places along the 88-108MHz band
    I am worry from that in the sme unit the sender hear himself
    If this occur my project will fail ans so my efforts so please tell me and advice me how to do this and what must i do


  7. Talking in terms of positive and negative voltages is a bit missleading....

    I agree because this exactly what they teach us in schools

    guru start by this answer to force andrie to use his mind, guru is a good man

    with NPN Tr we connect collector to point more positive than emetter and make the tr ON by aplying a +tive voltage >= 0.7 V 

    with PNP Tr we connect collector to point more negative than emetter and make the tr ON by aplying a -tive voltage <= -0.7 V 

  8. e) When Ic is high (look at Fig VD01 below) hfe (beta) is low, Zin is low
      and VBE is high (Look at Fig VD02 to see how VBE changed with IC)
    f) When Ic is high it will drain your batt quickly


    I want (as u may noticed in the figures) that Ic = 2mA
    2mA means Isat 4mA
    4mA = 9/[RC+RE] 
    [RC+RE] = 9/4m = 2250
    RC= 10 RE ==>  11RE = 2250  ==> RE = 204.5 ohm take it 200 ohm (two 100 in series)
    so, RC =10 RE = 2K ohm

    your Zo = RC = 2K, so Zin2 must = 20k at least to not affect Av1

    STEP 2

    For symmetrical swing up and down, VCE = VCC/2 = 4.5V
    Remain 4.5V from the 9V batt, these 4.5V divided between RC and RE according to their values
    4.5/11 = 0.41v, so, V(RE) = 0.41V and V(RC) = 4.5 - 0.41 = 4.09V
    The number 11 arise from the fact that RC contribute by 10 and RE contribute by 1, total=11

    STEP 3

    At Ic = 2mA, beta = 200
    so, IB = 2m/200 = 10 uA
    Id (the current pass through R1 and R2 with no transistor connected) = 10 IB = 100uA
    Id = VCC/[R1+R2] = 9/[R1+R2] ==> [R1+R2] = 90 K
    We calculate VE as = 0.41v and from the curve VBE = 0.64 SO, VB = 1.05V

    I(R2) = Id - IB = 90 uA ==> R2 = VB/V(R2) = 1.05/90 u =11666.7 ohm take it 12 K ohm
    R1 = 90 -12 = 78K , connect 68K in series with 10K

    STEP 4

    Zin = R1//R2//[hfe*(re+RE)]
    re = 26 mV/IC = 13 ohm
    so, Zin = 10.4K // 42.6K = 8.4K (fairly low i'll discuss this later)
    the o/p voltage can swing from [VCC] up to [VC- Isat*RE] down, that is it
    will swing from 9V to (4.91 - 4m*200)= 4.11v
    this swinging ac signal is carried on a VC dc voltage
    The max upper peak of this signal which represent the negative part of the
    i/p ac signal, = VCC - VC = 9 - 4.91 = 4.09 V
    The max lower peak of this signal which represent the positive part of the
    i/p ac signal, = 4.11 V
    Note the symmetric it is very close to 100%, thanks to Mr AUDIOGURU for every thing.

    To increase Zin, u have to lower IC and recalculate the other values.

    Later I'll continue my discussion about:
    bypassing the whole RE
    bypassing part of RE
    choosing the caps value between stages
    discussing a real designs and show if this is good or bad ...

    I hope guru read this and put his golden comments
    thank u all



  9. hi all
    Hi audioguru... my big teacher
    I'll show you here what guru taught me in the last 5 pages, then we'll
    continue to reach a high level... hope so

    (1) design a preamp (voltage divider unbypassed)
    (2) using the famous PN2222A transistor whose datasheets are attached below
    (3) I need a voltage gain of 10 for low distortion.
    (4) I have a 9v batt as a power supply (VCC).


    STEP 1

    Av (the voltage gain) = RC/RE = 10, so RC=10 RE and V(RC) = 10 V(RE)
    Before u choose RC and RE values u must consider the following:
    a) the value of RC = o/p impedance (Zo)
    b) If this stage have a load like a second stage follow it then the total
      Zo= RC//Zin2
    C) Zin2 must be >= 10 RC to not load down the 1st stage and decrease its Av
    d) IC = IE = Isat/2 , where Isat is the saturation current and we choose its
      half to be at the center fore symmetrical swing of the o/p signal
            Isat = VCC/[RC+RE]

  10. Hi
    I back again to this very important subject
    first thank you audioguru you do a good work to make me understand
    i print this 5-pages subject after editting it in WORD and finally have 19 A4 pages
    i take it with me every where reading them. it is hard to read directly from the computer screen, i need to underline the important and new aspects and compare bwn some replies
    When I finish it I'll either put a detailed design or continue asking question and god help guru

  11. OK Mr audioguru
    I may understand the general aspect of what u said but
    can u give me an example about this especially on your FM transmitter circuit.
    where the subcircuit or the parts that  do the pre-emphasis
    also in the receiver where it be placed in the whole circuit
    thank u audioguru

  12. It is just a DTMF tones decoder. It has nothing to do with a radio.

    i understand that it require a separate FM receiver

    Get a good datasheet from www.datasheetarchive.com .

    i use this link but i have not any results
    but in this          http://www.alldatasheet.com/              i faound many

    If you use an ordinary FM broadcast band radio then it has de-emphasis and the transmitter that you use must have a matching pre-emphasis.

    i'm not understand this statement

    thank you

  13. (1) I read carefully the CM8870 datasheets but I can't conclude that it can
        receive the FM signal directly or it must be connected to a separated FM
        receiver please tell me
    (2) I hardly got the datasheets of CM8870/70C, but i really have CM8870PI
        Is there any difference?

  14. All I'm looking for is a basic radio electronics tutorial that covers how things fit together in a receiver and a transmitter. Something perhaps that teaches me how to apply the circuit analysis I know as of now to radio circuits.

    This is also my problem, how to relate what you study with the practicle projects
    if u can't you waste five years in a universty

    all text books, net and persons talk about every thing but not about what you want

    i hope someone help u and me
  15. I'm sorry, lets forget what i said before and start again ....

    the emergency neon lamp has a rechargable 6v rectangular batt

    if i want to charge it using 7.5 to 9 volt power supply and want to stop the charging process when the batt is fully charged using a voltage comparator

    at what voltage i must stop

    thank you

    Hello Walid!
    I think temperature is the most critical criteria to stop charging. If u have lot of experience charging non-rech bats than u can tell us the avg time to charge common cells like AA, AAA or D. It will be usefull

    Hi Mr Muhammad Abu Bakar, in fact i want to learn about batt charging and how the designer make a decesion in chossing his components and not to measure temperature and ave time

  16. ok ok ok

    i want to tell you that i recharge unrechagable batteries for years and reuse them
    it is never explode
    i have not faced any problem with them and after recharge them the last long time specially in remote control and sound toys

    i want that info to stop the charge process whe it must stop
    can you help me?

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