Modulated signal and loaded to ground

Discussion in 'Homework Help' started by TBayBoy, Sep 27, 2011.

  1. TBayBoy

    Thread Starter Member

    May 25, 2011
    148
    19
    In the attached circuit L2 is a diode loaded inductor, however in some of the boards we usd there was a 220Ω resistor.

    The question is whay is this component needed, and my first inclination is it allows the tank to build the negative half of the modulation.

    Am I out to lunch??

    :)
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    One observation without knowing component values would be that L2 perhaps presents a low impedance to (& thereby attenuates) the out of band unwanted low frequency components.
     
  3. TBayBoy

    Thread Starter Member

    May 25, 2011
    148
    19
    Well I have a 150kHz carrier wave, with a 1kHz audio wave, so after the diode I have a 1kHz envelope with 150kHz inside, but only the + parts of the wave. Then the tank forms the negative portions as mirrors of the positive so the input to the tank is a 0-300mV wave, and the output is a 600mV peak to peak audio modulated signal.

    Some boards had the L2 and some had a 220Ω resistor, but gave the same output.
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Interestingly I found this modified circuit simulation seemed to do the job OK.
     
  5. TBayBoy

    Thread Starter Member

    May 25, 2011
    148
    19
    Thanks for the help, more talking and info that component is used to forward bias D1
     
Loading...