Reactance modulation...

Discussion in 'General Electronics Chat' started by aj_snowfire, May 26, 2010.

  1. aj_snowfire

    Thread Starter New Member

    May 19, 2010
    16
    0
    guys in tthe schematic its a reactance modulation,my confusion is about the output signal from the oscillator,
    guys from wich point can i take the output signal from the tank circuit to the next buffer amp stage...in the
    schematic,do u think the output can be taken out from under the inductor to the next buffer amp stage,please
    help me,its very crucial thing for me now,thank u
    i think the output must be from the collector of the transistor,am i right or wrong,if wrong,please correct me,
     
  2. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    Replace the LC with an R and it's a standard common-emitter amplifier - the LC just means you'll get an output peak at the resonant frequency. As you've already got it set up in LTSpice, try sweeping the input frequency at V2 and observe the output. Watch out for large output magnitudes - add an R in parallel with the LC to increase the damping if it all gets a bit out of control, you don't want to blow up the transistor or the next stage. This is where SPICE becomes very useful. Add another R in series with the LC to limit the collector current if you like.
     
  3. aj_snowfire

    Thread Starter New Member

    May 19, 2010
    16
    0
    i think the emitter resistor sets the collector current,so the Ic will be 10mA,
    do u think the voltage at the collector can go more than 24V...
     
  4. aj_snowfire

    Thread Starter New Member

    May 19, 2010
    16
    0
    cause the DC supply is just 12V,and i think the swing at the collector cant go more than 24V..
     
  5. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    OK, assumed you had LTspice, as I recognised the schematic style. If you don't, it's a free download from Linear Technology. Just for you aj I have simulated your exact circuit, and the output is a maximum of about 2.8 V at about 90.8 MHz. Reduce the emitter resistor to 30 ohms and it's 15.3 V at 89.1 MHz. 3 ohms and it's 300.7 V at 77.8 MHz. Now go download LTSpice IV and have a play... hours of harmless fun.
     
  6. aj_snowfire

    Thread Starter New Member

    May 19, 2010
    16
    0
    man i know,if u decrease the emitter resistor gradually the current Ic increases...and also increases the voltage swing at the collector,and i have been using LTspice for months..
     
  7. aj_snowfire

    Thread Starter New Member

    May 19, 2010
    16
    0
    as per my knowledge, i know that the collector has high impedance and the emitter has low impedance,so its better to take output from emitter itself,wat do u say
     
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