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Ferrite rod antenna explanation

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

  1. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    hello to everybody,
    can some help to make a ferrit rod antenna and to explain me thnx

    is for am radio, trf regenerative

    i have a ferrit rod 90mm diameter, and i have 0.5mm wire magnetic

    thnx
     
    Last edited: Apr 9, 2018
  2. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    this is the schematic , i make also the am receiver, but i dont know the ferrit rod(is problem i try to make but the radio dont work)(simpele i dont know how to make a ferrit rod antenna) REGEN 3.jpg
     
  3. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    I have never seen a ferrite rod 90mm diameter, they are more likely to be 9mm diameter and 100 to 150mm long.

    The schematic looks to be a medium wave receiver. Do you have strong signals in yout area.

    Make a wooden rod the same diameter as the ferrite rod.
    Wind some paper around it and glue with PVA to make a tube.
    Put a dint in each end of the wooden rod so that it can be rotated on two spikes or put it into a hand drill, my lttle drill has a 4:1 gear ratio.
    Wind on L1 with the turns touching. Glue the ends down perhaps with hot melt glue Slide off the rod.
    Wind on L2 and L3 side by side in a similar way.
    Put the two assemblies on the ferrite rod spaced at a few mm.

    The ferrite rod is very brittle so should be handled with care.
    Some PTFE plumbers tape wound on the wooden rod may make the coils easier to extract.
    The position of the coils on the rod can be fixed with traditional beeswax but I tend to favour hot melt glue as it can be removed cleanly.

    If you break the rod, it can be glued together with epoxy with little degradation in performance.

    A scrap transistorised radio may well have a ferrite rod complete with L1 and Cv
     
    poor mystic and michael1978 like this.
  4. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Sorry man, i just dont understand so good, because is my 4 times that i make bad ferrite, i know i make mistake,

    i have signals,

    i try i search i on internet for ferrit rod, i make nervous, i dont find nothing easy

    you mean wooden to hold the ferrit rod?

    so in the ferrit rod, to wind a paper with glou after to wind the L1, to glue the ends of L1 , and for L2 and L3 the same so they can move L1 L2 L3 with the paper right and left right to the ferrit rod?

    what if L1 magnetic wire touch L3 of L2, is a problem, of i have to tape?

    like this
    Loopstick_003.jpg

    thnx man
     
    Last edited: Apr 9, 2018
  5. davenn

    davenn Moderator

    13,260
    1,748
    Sep 5, 2009
    where did you get this circuit from ?
    do you have a link ?
     
  6. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    yes of course here https://imgur.com/a/JpwJs
     
  7. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    The wooden rod is used so that you do not have to wind the coils on the delicate ferrite rod.

    L1 should be separated from L2 and L3 because of capacitive effects.
    You seem to have done a very neat job.
     
  8. Audioguru

    Audioguru

    2,570
    580
    Sep 24, 2016
    You show a TL081 opamp with its (+) input connected through R6 to its negative supply that is 0V then it is not biased [properly. Then it will do nothing because its inputs MUST NOT be within 4V from either supply voltage (the datasheet says so as its Common Mode Input Voltage Range). What is the load for the TL081 opamp? Its output current is too small for it to drive a speaker or a 34 ohm headphone. Use a power amplifier instead.

    The detector diode also will not work because it is continuously conducting because a coupling capacitor must feed it. Luckily the diode feeds the DC voltage from the emitter of Q2 as a little bias voltage for the opamp input.
    If the radio signal is very strong then rectification from the diode will bias the input of the opamp for the TL081 to work.

    The detector diode is not needed anyway when the circuit is designed properly because a regen radio detects AM without it.

    I looked in Google for Regen Radio Circuit and did not find the one you have but I found many circuits with a power amplifier and no detector diode.
     
    michael1978 likes this.
  9. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    did you look the site?
    so to make it seperate L1 and L2? so i have to make everything seperate in ferrite rod,
    for that i say i dont know how to make ferit rod,
    thanks
     
    Last edited: Apr 10, 2018
  10. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    i found here https://imgur.com/a/JpwJs, and they say you can use lm368, but my problem is ferrit rode, thanks
     
  11. Audioguru

    Audioguru

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    580
    Sep 24, 2016
    No, you typed the numbers backwards, the power amplifier is an LM386.

    My post mentioned all the other problems that you have with that poorly designed circuit.
     
    michael1978 likes this.
  12. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Rely, man compliment, you are a specialist to find the problems.....;-)
     
  13. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Audioguru, i search al long to find easy for me, yes you are right without detector i see a lot, but this one was very useful something special, with picture how to connect it was very easy for me
     
  14. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    I make a ferrit with paper and glue i winding
    Hey man, i make it ferrit rod, i make one paper long like ferrit rod long, and i make it with glue the paper, i wind L1 and L2 and L3 with few mm seperate, and i think is working is 4.4v to transistor 1, and i have one small oscillscope, so the regen is working, the signals out from diode is in mili volt, but now the problem stay to amplifier, i connect a lm386n4, like they say in site link, you can use lm386, but i get nothing signals, is not working like he says Audioguru, do you know how to fix it? thank man for helping me to make ferrit rod antenna.....
     
  15. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Audioguru, i fix it the ferrit rod antenna, now can you help me how to fix it power amplifier i use lm386, but i dont get any signals, what i have to change please........
     
  16. Audioguru

    Audioguru

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    580
    Sep 24, 2016
    You can build this lousy, wrongly designed circuit then fix its problems one-by-one like I did with the FM transmitter that I fixed its 4 problems.
    1) Make a Super-regen that adjusts its regen amount by itself instead of this ordinary regen that you must fiddle with its regen control.
    2) Capacitor-couple its audio output to an audio power amplifier (without using a detector diode).

    First fix this lousy circuit. You did not say where you measured 4.4V on transistor 1. On its collector would be good if the supply measures about 9V. Then it can regenerate a signal if the coils are connected with the proper polarity. The base-emitter of transistor 2 will reduce the signal DC voltage to about 3.75V. The diode is not needed and reduces the DC even more. A capacitor coupling the audio to the input of the LM386 power amplifier should work if it is the correct value. Please post your new total schematic.
     
  17. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Audioguru first let me to make work amplifier, second i gonna do it enough experimetns i make it like here, when i change pot regen is 3.2 to 5V transistor 1,
    REG 2.jpg
     
  18. Audioguru

    Audioguru

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    580
    Sep 24, 2016
    I doubt that maze of wires on a solderless breadboard will work like a radio.
    Like most IC audio power amplifiers, the LM386 has a frequency response higher than 1 megahertz so it will probably oscillate like mad when connected on a solderless breadboard with the capacitance between all the rows of contacts and long connecting wires.
    Please attach the schematic of your complete circuit, especially your LM386 that is not shown in the photos.

    The regeneration pot P1 should not affect the DC of the first transistor since it is AC coupled with capacitor C4 that blocks DC. Maybe you have the regeneration turned up too high which causes the first transistor to oscillate and produce a maximum output.
     
  19. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    Goodmorning Audioguru, i have to make seperate breedboard lm386, i goona make tuday and i goona put here, thanks.
     
  20. Audioguru

    Audioguru

    2,570
    580
    Sep 24, 2016
    Do not use a breadboard for an LM386 because the capacitance between the many rows of contacts and wires will probably cause it to oscillate at a radio frequency and get hot. When it is oscillating then it cannot amplify audio. Solder the LM386 and its capacitors on a compact stripboard or pcb instead.

    Will you remove the TL081 opamp from the radio circuit?
     
    michael1978 likes this.
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