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10.7 MHz oscillator with transistor

Discussion in 'Radio and Wireless' started by aurelZ, Jul 17, 2019.

  1. aurelZ

    aurelZ

    63
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    Jun 10, 2019
    hello
    I found few circuits on net about 10.7Mhz oscillator and i build it with parts I have
    but it looks that no one of them not work ,in another words not oscillate.
    any help?
    anyone know for one tested with transfilter 10.7 mhz that work ?
    thanks
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,277
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    Nov 17, 2011
    How did you build them? On a PCB with good layout or on a breadboard with lots of parasitic capacitances? Oscillators are notorious for requiring a good build to work properly.
    Here are some hints for good prototyping.
     
  3. aurelZ

    aurelZ

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    Jun 10, 2019
    Hi
    That is for total beginners and is ok.
    I have built many fm oscillators transmitters etc and all work with or
    without good layout ,main thing is transistor type and his working point.
    Unfortunatelly i have no luck with this one of 10.7Mhz
    why i need that ?
    I was asking for some working and tested circuit on 10.7 mhz to test
    fm detector or better to say to adjust it on proper frequency.
     
  4. aurelZ

    aurelZ

    63
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    Jun 10, 2019
    For example look this simple circuit.
    it is almost typical fm oscillator -transmitter.
    i use fabricated choke of 3.3 uH with 68pF which should give 10.7mhz
    as resonant frequency but circuit simply not oscillate.
    or i need to add some audio signal to it to test is something on output?
    thanks Oscillator_10.7MHz.gif
     
  5. Ylli

    Ylli

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    Jun 19, 2018
    With a 3 volt supply, your biasing is going to be fairly critical. As shown, the 2n3904 is not biased on at all. Try reducing that 39K to a 10.1K.
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009

    ummmm .... 10.7 MHz oscillators are not normally use for transmitters as this is a very common Local Oscillator in receivers.
    You really shouldn't be transmitting on this freq as it will upset everyone in your local area


    I strongly suggest you look at using a different frequency

    I also strongly suggest that if you are going to play with RF oscillators, You really must have a
    frequency counter to know exactly what frequency you oscillator is producing


    Dave
     
  7. aurelZ

    aurelZ

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    Jun 10, 2019
    davenn and otthers..
    I really don't know why my question is too complex.
    of course i don't want to transmit anything on 10.7MHz
    I just want to build this oscillator for testing I.F. 10,7Mhz amplifiers and demodulators.
    So i need one good -tested circuit for that purpose only
     
    davenn likes this.
  8. davenn

    davenn Moderator

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    Sep 5, 2009

    I did assume that was a possibility but when you showed a circuit with an antenna it suddenly looked like you wanted an on-air transmitter
    and hence my warnings

    Anyway, regardless, you cannot build RF gear without proper test equip and the bare minimum is a decent frequency counter
    so that you cant get the osc. on 10.7MHz instead of who knows where


    Dave
     
    Last edited: Jul 18, 2019
  9. aurelZ

    aurelZ

    63
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    Jun 10, 2019
    Ok
    and with 10.7mhz transfilter
    which force circuit to oscillate around 10.7 mhz?
     
  10. davenn

    davenn Moderator

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    Sep 5, 2009

    A what ? never heard of one
     
  11. Martaine2005

    Martaine2005

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    May 12, 2015
    What is a dedicated 10.7Mhz transmitter for?
    You have been asking different questions in different thread/posts.
    Simple test equipment can supply your 10.7Mhz

    Martin
     
  12. aurelZ

    aurelZ

    63
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    Jun 10, 2019
    A what ? never heard of one
    and now i will say what?
    you don't know what is ceramic transfilter or caramic resonator with 3 leg for 10.7mhz?
    i cannot believe !
    YES i pos two question in hope that someone here have or build and test such a
    oscillator.
    Purpose of such a circuit is simple; testing I.F. 10.7mhz stages in fm receivers.
     
  13. davenn

    davenn Moderator

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    Sep 5, 2009

    ceramic resonator yes a standard item, used dozens of them ....
    never heard anyone but you call them a transfilter and I have been into RF electronics for 40+ years

    So you can see it helps to stop confusion by calling them by the correct name


    OK I don't have a dedicated 10.7 MHz osc, I just use my signal generator
    I will have a look around to see if I can find an appropriate stand alone osc circuit

    As I asked before .... do you have a frequency counter ? You WILL need one
    You are not going to get an osc on the correct freq without one

    so how do you know that circuit you posted above doesn't work ??
     
    Last edited: Jul 19, 2019
  14. aurelZ

    aurelZ

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    Jun 10, 2019
    Yes good question ..how i know
    Simply ,when i connected it on my fm demoulator which output is connected to
    audio amplifier ,there is no any sound or hiss.
    i know it is better to have solid signal generator but who can have all that instruments.
    Anyway i found one simple circuit build with old AF106 transistor.
    Yeah very old...i know .
    Also i use transistor what i have at hand and it is S9014.
    When i first time tried i use choke 3.3uH with 68pF which resonant freq is around 10.7
    but it looks that oscillator don't like chokes(probably because of large imedance) so
    i see on that old shema what kind of coil author of circuit use.
    it is small 5 mm dia plastic holder with ferrite core pulled from old TV set.
    I have this on and i wind 10 tuns of 0,1 mm wire and voila circuit work.
    How i test it..simple....
    Output of oscillator is trough 120pF cap used from emitter of transistor.
    On base of transistor i connect audio signal from my kenwood receiver trough 10nF capacitor
    when i moving this small ferite core sound become strechy or become more clear.
    so oscillator work .
    To test it more i replace output cap 120pF with ceramic (trans) filter 10,7Mhz and
    work the same with just small adjustment.
    Here is a shematic of oscillator which is really easy to build and work on just 3V battery.
    OSC10_7MHZ.gif
     
  15. aurelZ

    aurelZ

    63
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    Jun 10, 2019
    Finished circuit which is TESTED and work very well.
    FM10.7MHzOsc.gif
     
    davenn likes this.
  16. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    How do you set the frequency of your "Small signal generator" to 10.7 MHz? I see no sign of the ceramic resonator thingy on your schematic in post #15. And why would you trust such a device to accurately provide 10.7 MHz? I thought they were more in the nature of band-pass filters, rather than oscillator frequency-determining devices. You didn't even include a datasheet for your so-called "transfilter," so hows about uploading one, or at least a link to it?
     
    davenn likes this.
  17. davenn

    davenn Moderator

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    Sep 5, 2009

    how do you know? have you measured the frequency with a frequency counter ?
     
  18. aurelZ

    aurelZ

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    Jun 10, 2019
    How i know ?
    Simple because i use transmission ceramic filter 10.7MHz
    see post #14
    In last schematic you can see output capacitor of 120pF.
    I add that 10.7 Mhz ceramic filter with 3 leg to input of my weiss FM demodulator.
    So RF signal goes from this 120pF cap to ceramic filter of 10.7Mhz.
    And only signal of this frequency (+/- few kilohertz) can pass trough ceramic
    filter...right?
    Coil in LC tank is with ferite core so i can adjust oscillator to proper frequency.
    transistor S9014 is not good for 10.7Mhz oscillator .
    One my friend confitm me that.
    So i use 2N3904 which is excellent ( use any VHF type) or 9018 or BF199 or C3355.
    To prevent any audio leak detector/demodulator and oscillator/signal generator each of them use
    separate power supply also as audio amplifier on which is demodulator output connected.
    I hope that now is much more clear.
    TEST107MHz_BLOCK.png
     
  19. aurelZ

    aurelZ

    63
    7
    Jun 10, 2019
  20. hevans1944

    hevans1944 Hop - AC8NS

    4,225
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    Jun 21, 2012
    Much more clear? Not really. You still haven't provided a part number for the ceramic filter you used.

    But, as long as you are happy we are happy. I personally don't believe you know diddly about RF circuits, or their design, but generations of amateur experimenters before you didn't let that bother them either, pressing ahead by guess and by golly until they got something that sorta worked. Go read about how Guglielmo Marconi did it. He probably learned that paradigm from Thomas Alva Edison. It worked for light bulbs, but not so much for radios.

    Edison discovered vacuum tube thermionic diodes (see Edison effect) in 1880, which later became important as sensitive RF demodulators, but he was looking for a way to prevent blackening of the interior of his new light bulbs... the Edison effect didn't work for that, so he made a note of it and then promptly forgot about it. John Ambrose Fleming re-discovered the Edison effect and in 1904 used it to make a practical thermionic vacuum tube diode RF detector. Lots of opportunities for design by guess and by golly in the early days of radio, although by the time Edwin Armstrong invented FM radio, rather straight-forward and sane procedures were already in place.

    It is possible to use a ceramic band-pass filter as a frequency-determining circuit component, as you may have discovered, but that doesn't mean it will produce a stable output at an unvarying frequency. These devices are highly temperature sensitive and the oscillator frequency that is produced will wander all over the place. That may be "gud enuf" for getting sound through a receiver's intermediate amplifier (IF) stages, but it is not the recommended way to perform an IF transformer alignment. But, whatever works for you is okay with us. We are here to help, but some people prefer different paths. Good luck with that.

    There are devices, called ceramic resonators, that are sometimes used as frequency-determining components, especially at low frequencies where crystal oscillators become large and unwieldy. However the trend in the 21st century seems to lean toward digital synthesis from a high-frequency master oscillator whose output can be frequency divided with binary counters. This has led to the availability of low-cost signal generators available for build or purchase by even cash-strapped experimenters. Maybe you should look into that.
     
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