Adjustable low pass filter

Discussion in 'The Projects Forum' started by saurabhkarnik, Aug 15, 2008.

  1. saurabhkarnik

    Thread Starter Member

    Jun 22, 2008
    22
    0
    hey guys... could u please tell me if it is possible to design an adjustable LPF between 100hz-1Mhz by using varicap or something.... what i'm talking is it possible or completely hypothetical... if not possible in what frequency ranges should i use different adjustable filters
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    A varicap is used at 100MHz, certainly not at 100Hz.
    You might be able to find a varicap used for an old AM radio that tunes down to 540kHz.

    20 or 30 years ago a "transconductance amplifier IC" was used as the variable resistor in a lowpass filter. CA3080, LM13600 and LM13700 rings my bell.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    100Hz to 1 Mhz, the range is a bit wide. It might be possible to make an active filter, but not very likely. 100Hz to 10Khz is a lot closer I would think.

    In the case of an active filter the variable component would be a resistor or two (you can gang resistors on one shaft).
     
  4. saurabhkarnik

    Thread Starter Member

    Jun 22, 2008
    22
    0
    how about this
    if i make a rc filter cutoff will be given by 1/rc..
    so if i use a pot or a varicap and use stepper motor to vary it by microcontroller is it possible...
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    It seems to be possible. Take a look at this commercial product (PDF).

    Greetings,
    Bertus
     
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