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

 

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.

 

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).

 

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...

 

Hello,

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

Greetings,
Bertus