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sBitx xtal filter

 

Please give more details on how-to calculate (and build) the 40MHz xtal-filter.
When I calculate values for ladder filters at 40MHz I get a maximum bandwidth of around 10-12kHz.

Niels, oz9ny
 

I did a brute force method.
1. I used a QER filter.? This is an evolution of the Cohn filter that has equal capacitors. It has paralleled crystals in the end points.
2. I started with 4.7 pf capacitors and variable resistors on either side.
3. I swept the filter on Antuino. The bandwidth was too short.
4. I decreased the capacitors to 2.2pf, the bandwidth proved enough (30 khz). I adjusted the terminating resistors to eliminate the ripple.
5. I replaced the terminating resistors with L network to do the impedance transformation.
- f

On Tue, Nov 9, 2021, 9:19 PM Niels Jalling <niels@...> wrote:
Please give more details on how-to calculate (and build) the 40MHz xtal-filter.
When I calculate values for ladder filters at 40MHz I get a maximum bandwidth of around 10-12kHz.

Niels, oz9ny

 

¿ªÔÆÌåÓý

10 to 12 kc?? would make a nice roofing filter on a double conversion :-)

dg9bfc sigi

Am 09.11.2021 um 16:49 schrieb Niels Jalling:

Please give more details on how-to calculate (and build) the 40MHz xtal-filter.
When I calculate values for ladder filters at 40MHz I get a maximum bandwidth of around 10-12kHz.

Niels, oz9ny

 

This is a 30 KHz filter.


On Tue, Nov 9, 2021 at 10:11 PM Siegfried Jackstien <siegfried.jackstien@...> wrote:

10 to 12 kc?? would make a nice roofing filter on a double conversion :-)

dg9bfc sigi

Am 09.11.2021 um 16:49 schrieb Niels Jalling:
Please give more details on how-to calculate (and build) the 40MHz xtal-filter.
When I calculate values for ladder filters at 40MHz I get a maximum bandwidth of around 10-12kHz.

Niels, oz9ny

 

Thanks. It's like "The Bumble Bee Myth" :-)
de oz9ny

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