Low pass passive bessel filter

Discussion in 'General Electronics Chat' started by Gaz250587, Feb 27, 2008.

  1. Gaz250587

    Thread Starter New Member

    Feb 27, 2008

    I need to design a low pass 6 pole bessel filter (passive) for a pre modulation filter - Bassicaly it cuts off the high frequencies of a square wave to reduce RF transmission bandwidth. Cuttoff is 7MHz, impedence is 50 OHM

    I put together an lC filter and tested it, but it was resonating quite a bit at around 7MHZ (I was getting about 8 or 9 volts on the output, with a 5V input), I tried a 6.5MHz cuttoff and it was still resonating but at a slightly lower frequency.

    I was told that it would need dampening resistors to remove the resonance.
    Any ideas on how to go about designing an LRC or RC bessel filter? There seems to be very little information that I can find in books or the internet.

    Thanx for your help
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007