Deisgn a filter of 8MHz BW at 15.42MHz with 4K impedance

[brmadhukar]

Hi,
I need to deisgn a filter of 8MHz BW at 15.42MHz with 4K impedance. I know the inductor values will be high. If were to use a lesser impedance I shall be able to do it with practical values. For this I want to reduce the filter impedance and use a transformer to step up impedances. Is it practical, wher do I get these transformers and how do I do it.

Thanks in advance
madhukar

 

[armsgroup]

Hi
why u don't try active filter rather than passive one I think u can control the impedence mathing better with active device

 

[spweda]

FIlter Match

There some other impedance structure such as T, Pi netwrok which may fit your requirement.

 

[flatulent]

transformer problems

At these frequencies, transformers have problems at these impedance levels. I tried a traditional design and got several 1 pF capacitors. You will have trouble with parasitic resonances in the inductors and PC layout.

How about using RF op amps with a series 4 k ohm resistor from the driving one to the filter and a shunt 4 k ohm resistor at the output op amp in the ususal inverting two resistor circuit configruation.

Another trick is to use coupled resonator type filter with taps on the end resonators for interfacing to the lower impedance outside world.

One other problem is your bandwidth being about 50% of the center frequency. You may be better using a high pass and a low pass filter in a row. (tandem) with an amplifier stage between them.