Butterworth bandpass filter question

I am trying to scale an existing front end receiver (butterworth
bandpass) filter to a different frequency range. Unfortunately, it has
a transformer in the original design, so I'm stuck. I also don't know
how to handle the load presented by the active front end component
other than it's probably not significantly reactive.

The existing filter is for a 7 Mhz receiver, I'd like to have a
similar filter design for 50 to 200 Khz.

The filter components and transformer winding details are in the
document at:

http://www.amqrp.org/kits/softrock40...0Assy%20v1.pdf

The input chip is an FST3126, spec sheet is at:

http://www.fairchildsemi.com/ds/FS/FST3126.pdf

The spec for the T30-2 transformer core is at:

http://partsandkits.com/T30-2.htm

I have aade filter design software, but it isn't allowing me to plug
in the transformer into the design page of the software....so, I need
to know it's equivalent circuit I think.

The transformer winding details are on page 4 of the document and the
schematic of the front end is page 9. Ultimately, I need new values
for L1, L2, C20, C21 and C22.

If someone can give me a reasonable guess as to the equivalent circuit
of the transformer and the IC (U5), I can do the rest of the job
myself using the aade filter software.

Thanks,

T

On Sun, 11 Sep 2005 12:14:11 -0400, TRABEM <> wrote:
Get the free software program call RFsim99 lets you design buttrworth filters.

> I am trying to scale an existing front end receiver (butterworth
> bandpass) filter to a different frequency range.

=====================================

How do you know it is a Butterworth as distinct from other types?

A butterworth is a butterworth............in any discussion of the
butterworth filter, you will see this schematic.

Asking how I know it's a butterworth is a little like asking how I
know a car is a car.

However, I don't know it all.........perhaps it's closely related to a
butterworth, but called something else???

Let me know if I've made an error please.

T


On Mon, 12 Sep 2005 06:07:31 +0000 (UTC), "Reg Edwards"
<(E-Mail Removed)> wrote:

>> I am trying to scale an existing front end receiver (butterworth
>> bandpass) filter to a different frequency range.
>
>=====================================
>
>How do you know it is a Butterworth as distinct from other types?
>

<TRABEM> schrieb im Newsbeitrag
news(E-Mail Removed)...
> A butterworth is a butterworth............in any discussion of the
> butterworth filter, you will see this schematic.
>
> Asking how I know it's a butterworth is a little like asking how I
> know a car is a car.
>
> However, I don't know it all.........perhaps it's closely related to a
> butterworth, but called something else???
>
> Let me know if I've made an error please.
>
> T

Hello T,

a Bessel filter would have the same structure. The value of
the components define what filter type it is.

Bessel: max. flat group delay
Butterworth: max flat frequency response

You can also make a filter with this structure which is anything
between both types.

Best regards,
Helmut

>
>a Bessel filter would have the same structure. The value of
>the components define what filter type it is.
>
>Bessel: max. flat group delay
>Butterworth: max flat frequency response
>


Cool, didn't know that.

At VLF, the inductances are becoming quite large, requiring a toroid
core for even a simple inductor.

What are the advantages/disadvantages of each type relative to
inductor size requirements?

Maybe I should be looking at a bessel instead of a butterworth.......

GL to all.

T

On Mon, 12 Sep 2005 12:18:52 -0400, TRABEM <> wrote:

>A butterworth is a butterworth............in any discussion of the
>butterworth filter, you will see this schematic.
>
>Asking how I know it's a butterworth is a little like asking how I
>know a car is a car.
>
>However, I don't know it all.........perhaps it's closely related to a
>butterworth, but called something else???
>
>Let me know if I've made an error please.
>
>T
>
>
>On Mon, 12 Sep 2005 06:07:31 +0000 (UTC), "Reg Edwards"
><(E-Mail Removed)> wrote:
>
>>> I am trying to scale an existing front end receiver (butterworth
>>> bandpass) filter to a different frequency range.
>>
>>=====================================
>>
>>How do you know it is a Butterworth as distinct from other types?
>>

A Butterworth filter is a Chebyshev filter with No ripple in the passband.