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Posts posted by walid

  1. Hi guru
    Finally and after some effort I can borrow a high rolsolution cam and take some photos, please look below
    the first figure is for awhole SENAO SN-736 board for you to look
    the second is a close view to 3359 Ic and related components.

    I need your help and any help frome anyone here to enable me to take the suitable components to make a TX and Rx
    To reach this target, we shall preview many important aspects.
    i noticed that nearly all cordless phones have the same idea and same components with very small differences.
    Where is the Tx circuit in the first figure.
    Later I'll draw the shematic though it is double printed and hard to retrace but I'll do all my efforts.
    thank you.



  2. Your transmitter and your radio circuit are very different:
    1) The transmitter is wideband and the radio is narrowband. If something doesn't work properly then you don't have another narrowband station to test your radio with, and you don't have another radio to try the modified transmitter with.
    2) the limiter circuit has a line-level input but the transmitter has a microphone and a mic level input.
    3) The transmitter has pre-emphasis for good sound but it isn't used for narrowband.

    For these reasons I suggest to find the Tx in the same board. I know it send to another receiver but we can modify its freq to match our receiver.
    At this moment I lost my scanner (acer) software, I'll find one then I can send a photo of the board to get a help from u to find that Tx
    guru I fond to FM circuit, I dream to build my own walkie talkie.

    NOTE: during my search i found this page, it seems to be very important, i read it but can't understand what that modifications he did to get what?
  3. Hi guru, thank u very much.
    Please look at the figures below:
    (1) If I introduce this limiter between the mic stage and the remaining stages of your FM Tx, then it will function as a AGC, that is it control the amplitude of my voice so that the o/p freq BW about 6KHz or so?
    (2) My circuit board is SENAO SN-736, I think it have a transmitter circuit with freq different, if I can find it and modify its freq to match the 3359 receiver. I haven’t the second part of this phone. 



  4. Hi guru
    Hi Kevin
    Guru, you are the king here, at least for me.

    Learn about how a super heterodyne radio works from articles in Google.

    Learn about how radios work.

    I’m already learned about radios.
    I know u said that to escape from my 10,000 questions that will coming soon (smiling).
    Look guru, I read about radios more than u expects. Theories do not suffice my requirements to be an expert like you.
    During the discussions with u I got a valuable information that can’t get from hundreds of books.
    So I need your help to fly together in the electronic world.
    Lets start flying:
    If I follow the connections in the phone’s board, I’m sure that I’ll find the remaining RF, mixer and the local oscillator.
    I’ll draw the schematic by hand and scan it by a scanner and put it here for discussion.
    When two signals entering a mixer, then the o/ps of the mixer are:
     The sum of the two
     The difference of them
     The same signal 1
     The same signal 2

    So if sig 1 is the main i/p sig with freq = 10.7 MHz
    And sig 2 from a local osc with freq = 10.245 MHz
    Then one of the mixer’s o/p is the difference = 455 KHz so we use a ceramic band pass filter of 455KHz freq.
    I write this to convince u that I have some basics of radios.

    I forgot to say that this radio circuit is for narrow-band FM (telephone quality). My FM transmitter is for wideband high fidelity FM (broadcast quality).
    A narrowband radio will receive wideband signals with extreme distortion.

    (1) What the difference between wide and narrow bands  in numbers? Please    don’t disappointed from this question.
    (2) Can we modify your Tx to be a narrow band?

    Thank u guru and all members of this great communty.

  5. Hi
    Below I attached the datasheets of the MC3359P IC.
    I have a ruined cordless phone (SENAO SN736)
    From this phone I’ll get that IC and the related components, and with your help and some modifications, I want to build a FM receiver.
    Lets go:

    (1) What the meaning of RSSI written at the beginning of the datasheets?
    (2) Is this receiver possible?
    (3) For the following schematic (from the datasheets) and if I use audioguru’s FM Tx as a Tx, what is the 10.7 MHz i/p connected to pin 18?


    Remember that I have all the components in the schematic above from the phone itself.
    Thank you a lot.


  6. Practical Benefits of the Negative Feedback
    Most practical amplifier circuits use negative feedback for the following practical benefits:

    • Stabilization of voltage gain
      Decreasing output impedance
      Increasing input impedance
      Decreasing distortion
      Increasing bandwidth

    How NFB decreasing Zo, increasing Zin and bandwidth?
  7. Hi monoman

    >also a couple of circuit diagrams would really help (I am particularly interested in Frequency modulation radio)

    The following link is a practical book full with transmitters and receiver circuits
    if u read it carefully, you will find all what u need to know about FM also AM and antennas
    I hope it help u.

    while u  r reading, you can ask about anything obscure.
  8. Hi guru

    I was talking about the parallel resonant LC at the collector of the RF amplifier transistor on my FM transmitter. Its impedance is infinity at its resonant frequency without a load. But it is a terrible match to a 50 ohm antenna.

    I can't understand or accept that the LC impedance is infinity at its resonant frequency. Here is your formula:


    At resonance XL = Xc in magnitude and if they cancle each other because of phase.................... Yes Yes its impedance is infinity at its resonant frequency.

    But still some point obscure:
    If U GURU, for example, want to replace your C14 (=22p) in your FM Tx


    with a Pi C-L-C network as in that site: http://hem.passagen.se/communication/antenimp.html
    you have to know the Zout of the RF amplifier transistor (Q3) to match it with the 50 ohm antenna using the calculated values of caps and coil.

    May I worgly understood what the above link want to say, may be he want to tell me that the Pi C-L-C network match any Tx at 50MHz.

    so tell me what you have to do if u decide to use that network.

    thank u guru

  9. hi guru

    If they cancel then the Z is zero not infinity
    I know it is not zero
    the ohmic resistance of the coil wire and cap materials .. etec

    please look, the man who do this: http://hem.passagen.se/communication/antenimp.html


    the matching between Zout and the 50 ohm antenna using Pi C-L-C filter
    if Zout is infinity, how can he put the matching network
    to design the Pi C-L-C filter you must know Zout??

    Your last answers on this topic were not very good
    it takes me up then down, I'm confused now

    thank u

  10. Hi guru

    The calculator you found is WRONG!
    It has the wrong formula for the impedance at resonance of a parallel LC.

    yes I agree, it It has the wrong formula and they calc it as 220 and i calc it the first time as 110 and mistake when tell you it 220 ( I was hurry)

    You shouldn't calculate things at such a high frequency because you don't know how much stray capacitance is in parallel with your C, and you don't know how much inductance is in the wiring of the L.

    yes, I know, but still must calc it to know the o/p impedance to correctly fit the matching network, then may modify it lettle to compensare for the stray capacitance and inductance

    Here is another formula for the impedance at resonance of a parallel LC:

    I calc it, using your formula, look below:


  11. Hi guru

    I go to google and search for LC Resonance and one of them was:
    It is a calculator
    substitute L=330n and C=6.7p
    u will have f=106 MHz and Zo=220 ohm as i calculate it, it is not nearly infinite ohms
    It is very important to me to correctly calc the o/p Z of the oscillator because i want to discuss with u the pi C-L-C filter between this osc and the 50 ohm antenna from this site:
    and to ask u why u don't use it in your FM Tx
    don't worry i understand 95% of what he said but still to know how to cal the o/p Z of the oscillator to match it with the antenna
    I make a page in MATHCAD for quickly calculations
    thank u guru

  12. Hi aProgrammer
    thank u for fast reply

    Yes I agree, there are a mistake, the + and - inputs are inverted

    If they are
    Av = 1 + (R2/R1)

    but why they connect the (+) i/p  [the -ve in the figure] to adivider that half of VCC applied to it, why not simply connect R4 to ground and omit R3?

    To guru whose reply reached me just now

    Are u agree that there are a mistake, the + and - inputs are inverted
    I read your reply and I'll analyze it now:

    When you swap the inputs of the opamp you will notice that the input impedance of the preamp circuit is only 2.2k ohms which is too low for an electret microphone. A non-inverting opamp circuit would have a much higher input impedance so that an electret mic is not loaded down.

    from this i deduce that someone can swap the inputs of the opamp to get low input impedance if he want, and that the circuit as its work.

    For a very low resistance source, the gain at low audio frequencies of the inverting preamp circuit is R2/R1= 100. The impedance of the mic is in series with R1 so reduces the gain.

    thank u guru
  13. Hi guru

    lets do it again

    at 106MHz, L =330nH  and C=6.8pf, we have

    XL = 2 pi f L = 220 ohm
    XC= 1/(2 pi f C) = 220 ohm  (resonance)

    Ztot = (XL*XC)/(XL+XC) = 110 ohm

    I think it is wrong calc, Ztot must be zero because XL = j w L
    and XC = -1/j w c

    I don't know what to do............

    IF the LC impedance = 110 ohm as before, and the antenna impedance = 50 ohm

    110/50 = 2.2

    the turns ratio = sqr(2.2) = about 1.5:1  which equivalent to 3:2  = 6:4

    if the coil was 6 turns then the tap must be at the fourth turn and not the fivth turn to have better impedance matching.

    please guru correct me

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