Connect with us

Ferrite rod antenna explanation

Discussion in 'Radio and Wireless' started by michael1978, Apr 9, 2018.

  1. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    i remove tl081, I seperate but is no problem i go to solder lm386, and i with say when is finish
     
  2. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    is not working man, like my LM386 is not working i think, because the signal is the same with or without LM386
     
  3. Audioguru

    Audioguru

    2,607
    586
    Sep 24, 2016
    Test the audio amplifier with an audio input signal.
    You did not post the corrected schematic for the "radio" or for the LM386 amplifier so we cannot help you fix them.

    Also please post photos of the radio and amplifier you built.
     
  4. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    thanks ardioguru i make it, but again nothing, i search in google, there are a lot of lm386 configuration

    but you know what i did i destroy all,
    i make new radio TRF, can you please tell what is the problem, i can hear in 8ohm speaker, i hear in crystalearphone i find the stations, i hear, after i try to to make low 0 volume, you hear nothing, after i start voulme up i hear , when start more volume you hear noise not normal,
    here is the circuit
    choccy_trf_schematic.jpg
     
  5. Audioguru

    Audioguru

    2,607
    586
    Sep 24, 2016
    I saw the video of the Choccy Block radio and it played a lot of noise and distortion. Its audio power amplifier is awful because it has zero negative feedback. The datasheet for the LM386 shows how it should be connected and it has built-in negative feedback for very low distortion.
    I have never made a poor quality very simple Mickey Mouse AM radio like this one, instead I made normal super heterodyne AM-FM radios that worked perfectly.
     
  6. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    but he does not use lm386? in the circuits, i hear some station, when the volume increased i hear only noise,
    for me is perfect the radio, do you have and idea how to repair? where to check, can you help me please....
     
  7. Audioguru

    Audioguru

    2,607
    586
    Sep 24, 2016
    He made his own amplifier that is awful with no negative feedback. ALL audio amplifiers have negative feedback, but not the simple one he designed.
    A simple regenerative circuit makes an extremely poor radio that produces a lot of noise. I think yours begins to oscillate when you turn up the volume control. Increase the value of R14 and decrease the value of R1, then it will have less positive feedback.

    A real AM radio is a super heterodyne that has its input tuned, an RF amplifier with automatic gain control, an oscillator, a tuned mixer, an IF amplifier with 3 or 4 tuned transformer stages then a diode detector. It can feed an LM386 power amplifier.
     
    michael1978 likes this.
  8. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Man can just tell me, how much to increase the value of R14 i dont know and to decrase R1, and i will do it, i will tell you how is working?
     
  9. Audioguru

    Audioguru

    2,607
    586
    Sep 24, 2016
    Try increasing the value of R14 by 20% to 56k and reducing the value of R1 to 820. But a 10% change to 51k and 910 might work better. Maybe R14 needs to be 68k and R1 be 680.
     
    michael1978 likes this.
  10. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    thanks a lot, i go to change so i see one wire was out breedboard, so now is working perfect.....my first radio ;-)

    may i ask you something else i make you tired man, with my question without control ;-),
    you saw the page, do you understand how to calculate that ferrit rod, i search on the internet, i did not find nothing good, so why primary is main connected to the vc, and the secondary to input antenna, how they calucalte

    thank a lot for time
    have a nice wekend.
     
  11. Audioguru

    Audioguru

    2,607
    586
    Sep 24, 2016
    I am glad you fixed the wiring problem on the breadboard. Breadboards cause many problems.
    A normal radio has at least 5 tuned LC circuits to tune in the station you want but reject interference from all the other AM radio stations. This simple radio has only a single LC tuned circuit so it must have a very narrow bandpass. It has a narrow bandpass because it has more turns of wire for its tuned coil producing a high impedance than the coil that is loaded with the transistor.

    A good real AM radio has automatic gain control so that a weak distant stations sounds as loud as a strong local station. This simple radio does not have AGC.
     
    michael1978 likes this.
  12. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    thank, man i make it in the end.... now i have to study good this am radio. just for more experience.
     
  13. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Hi, how are you doing, this circuits wich i post it, i make the ferrit rod, but can you explain me how you calculate the ferrit rod, what is the formula of ferrit rod....how do you calculate,
     
  14. duke37

    duke37

    5,250
    723
    Jan 9, 2011
    The coils need to have a certain inductance to resonate at the wanted frequency.
    The number of turns on the ferrite rod controls the inductance and the permeability of the ferrite will ehhance the inductance. So put on a few turns and measure the inductance and increase to give the required amount. The inductance is proportional to the square of the number of turns and will be highest when the coil is at the centre of the rod.

    P.S You cannot make a ferrite rod. This requires complex powder metallurgy and a closely controlled furnace.
     
  15. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Hi Duke i dont want to make a ferrit rod, but i dont know how to select the inductane of L2 and L3, for example the circuit wich i post here, why how he calculate L2 10 turn L3 5 turns, why excactly 10 turn and 5 turn?
    thnx man
     
  16. davenn

    davenn Moderator

    13,319
    1,767
    Sep 5, 2009
    because those are the number of turns with a specific wire gauge required to give the needed inductance
     
  17. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    but is there a formula or if i want to make one ferrit rod anntena for myself, how, the L1 i know to connected with vc for desired frequency, but for L2 or L3 how can i know how much turn i need to make it? where can i get info for L2 or L3
     
  18. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    but how he know, where did he read
     
  19. duke37

    duke37

    5,250
    723
    Jan 9, 2011
    The formula for resonant frequency is F = 1/(2*Pi*Sqrt(L*C))
    If you want to pick up a transmitter on 640kHz with a 200pF capacitor, then you can calculate the required inductance by re-arranging the equation.
    A tuning capacitor will have a ratio of about 10:1 maximum to minimum. Because of the square root in the equation, this will give a frequency ratio of about 3:1.

    The turns connected to the transistor will depend on the impedances. A light coupling will give a high Q and good selectively, a tight coupling will give lower losses. I think that the turns of L2 and L3 will be determined by experiment.
     
    michael1978 likes this.
  20. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    you mean L2 or L3 they need to have low impedance to connect to base of transistor, can you please show just one example for L2 and L3, so after i know how to experiments, because i build the trf radio is working, only the output of ferrit rod i dont know, is there a formula to give

    thanks man.....
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-