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RF antenna incoming amplifier

Discussion in 'Radio and Wireless' started by stoveitin, Jul 3, 2014.

  1. stoveitin

    stoveitin

    16
    0
    Jul 3, 2013
    Hello,
    Been playing around with RF lately trying to learn about it and having a amplifying issue.

    Basically trying to transmit and receive a carrier frequency no modulation other than its on or off.

    I have a transmitter working and have a tank circuit filtering and receiving the carrier wave i can see it on a spectrum analyser incoming at about 20mv.

    Now i cant seem to amplify it at all to a useable level.

    I have tried many circuits using's transistors and mosfets. including ones other people have had success with.

    But all i seem to do is get the exactly same signal out as in with no amplification .

    Why is this ? any ideas on a simple transistor amp that would do this would be great. its operating at 16MHZ carrier frequency which is well within the frequency response of the transistors been using .. BC337 .. BC109 ..Mosfet 2N7000 no luck with any .

    Sometimes i believe the output from the amps or looked like it was really the probes picking the signal up acting as an antenna.

    i have got a tank circuit working with 1microH inductor and 100pf capacitor and you can watch it tune in using a variable cap as the signal strength varies obviously I set it when the strength is highest.


    Cheers for any help.
     
    Last edited by a moderator: Jul 4, 2014
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,219
    2,695
    Jan 21, 2010
    How are you measuring the signal? It's quite possible that if you're using an oscilloscope (for example) that it is the oscilloscope's leads which are picking up the signal, not your receiver. That would cause the symptoms you're seeing.

    Show us the circuits you've tried.
     
  3. davenn

    davenn Moderator

    13,351
    1,774
    Sep 5, 2009
    show us a schematic of your transmitter and receiver circuits


    Dave
     
  4. stoveitin

    stoveitin

    16
    0
    Jul 3, 2013
    Transmitter is basically just pierce oscillator .. using a transistor as the inverter outputting around 8 volts 16mhz on the antenna....I have been trying lots circuits tank circuit with antenna straight onto it and other side grounded.

    Then out put through a DC blocking cap into a amp...

    Amps have been using common emitter configuration as well as emitter followers ill put some drawings up later .

    yes was using an digital oscilloscope with then basic spectrum analyser mode seems to do the job and agree at some points the probe was acting as an antenna picking it up showing false readings.
     
  5. stoveitin

    stoveitin

    16
    0
    Jul 3, 2013
    drawing.jpg
    Roughly what been using..
     
  6. davenn

    davenn Moderator

    13,351
    1,774
    Sep 5, 2009
    OK,
    not really the best circuits

    for a start, here's a better osc for you
    use you 16MHz xtal instead of the 2 MHz one shown, it should still work OK

    [​IMG]

    I will look around for a proper receiver circuit for you :)

    cheers
    Dave
     

    Attached Files:

  7. stoveitin

    stoveitin

    16
    0
    Jul 3, 2013
    okay Cheers for the help my transmitter circuit is pretty poor but does seem to do the job ill try your suggested one out also, If you can find a simple easy to understand receiver that works would be greatful as reason doing this is trying to understand the circuit fully also hence the simple but not great circuits been trying so more of a learning thing than just banging something to together that works with no understanding.

    a lot of the receiver circuits use simple common emitter transistor amps with a tank circuit feeding them but I been having no such luck amplifying it so far.
    Cheers.
     
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