10MHz Miniature 4 Stages SMD Crystal Ladder Filter and a Test Breakout Board for it.

In Previous Videos I mentioned, that I started a Project for a 10MHz GPS Disciplined Rubidium Frequency Standard, including a Stratum 1 NTP Server and Multiple Isolated Outputs for 10MHz Square and Sine.
This was of course one of the Projects that was put aside, bcs my Focus turned to other Designs, well I picked it up again :-)
For that Project I Designed this 4 Stages Crystal Ladder Filter and the Test Breakout Jig way back when :-) as a Proof of Concept !
In the Video I show the Functionality but the Drawbacks of it too, which are, the high Attenuation. This is due to the SMD Crystals I use (not Matched at all) and that the in/Out of the Filter isn't matched either. Its a Proof of Concept and the PCB can be used for Better same Package SMD Xtals and other Value MLCC Caps, which means the Design can be Highly Tuned without changing the PCB Layout.
Nevertheless Tuned or Not, I plan to use a Post Amplifier to equalize the Attenuation.
The are Online and PC Based Crystal Ladder Filter Calculator out there, the Results can be tested fast with the Larger Test Breakout Jig, optimized and the tried out as Mini SMD Version.
Following some Links on Crystal Ladder Filter Calculators:
Narrow band-pass crystal ladder filters
www.giangrandi.org/electronic...
Quartz Crystal Bandpass Filter Design
www.changpuak.ch/electronic/Q...
Ladder Crystal Filters For Radio Amateurs (PC Version)
warc.org.uk/?page_id=387
Gerbers and Design Files are Available on Demand.
Please don’t forget to like and subscribe. Thanks for watching...
!!! Thank you to all my subscribers !!!
#electronicscreators
#crystalladder
#bandpass

[@michaelmayerhofer322]

The screen on the analyzer input shows the harmonics down approximately -55 dBc. The screen of the output shows the 10 MHz signal 45 dB above the base noise. So even, if the harmonics were still at -55 dBc, you would not see it, as the settings of the analyzer don´t give you enough dynamic range. You need to reduce attenuation and most likely reduce the RBW to judge the suppression of the filter.

[@KonstantinGrigoriadis]

Hello Thankyou, the goal was to show that even with non matched Crystals and non Matched Impedance's an effective attenuation is possible and by Fine tuning both the Design and the Measurement adequate results can be archived with Miniature 3.0x2.5mm SMD Crystals.
This was not meant to be a Final Design, rather using the PCB's as Playground for Optimization.

[@robertvandersanden]

Hi Konstantin, for a ham radio short wave receiver I have made a narrow band (400Hz) xtal filter.
I found the 3 xtal filter according to the giangrandi calculator the easiest as all crystals and caps are identical. The attenuation outside the passband is very high and the passband loss around 1dB.
It is important though to select 3 crystals which have their series resonances within 30Hz of each other. And don’t touch the crystals with your fingers when measuring their resonance as the increased temperature will cause drift. I used pliers to handle my crystals.
And when you calculate the filter to a certain impedance (this affects the bandwidth) step up and step down transformers are needed if the rest of your circuit is in the 50 Ohm domain. Having the filter itself at a higher impedance also helps to reduce the passband attenuation as the series resistance of the crystal becomes less prominent at higher impedances. An FT37-43 ring core with a couple of turns (5-8) works well here.
Note that a 10MHz crystal may give you a filter a couple 100Hz away from 10MHz, meaning your signal is just outside the passband and strongly attenuated. Carefully select your crystals from a batch to get to the correct frequency.
Regarding your measurements on your filter - without filter the higher harmonics are about 5.5 divisions down from the peak. With the filter in place the noise floor of the analyser is less than 5 divisions below the peak, so the harmonics may still be present, only no longer visible. A narrower resolution bandwidth for your measurement and slower sweep time will help to get the noise floor down.
Wish you success with your filter experiments!

[@KonstantinGrigoriadis]

Hello Robert, Thankyou, this Design was a Proof of Concept on how small I can get the Filter PCB and still be useful, using 2,5x3.0mm SMD Crystal and 0402 Capacitors, the target was a Size not much larger that a HC49 standard TH Xtal. The Breakout test board is the approximate Playground.
Merry Christmas and a Healthy and Prosperous New Year to you and your Family !
Cheers, Konstantin

[@robertvandersanden]

@@KonstantinGrigoriadis Hi Konstantin, the small PCB is certainly a nice achievement for fitting a 4 xtal filter.
Wish you and your family a warm Xmas and a good Newyear.

[@chrisdickens4862]

Neat concept.

[@KonstantinGrigoriadis]

Thankyou !

[@ghlscitel6714]

Maybe transformers at the input and output help a better matching of the impedances? Not sure, however.