Ceramic filter question

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Re: Ceramic filter question

Post by Jalex2 on Sun Apr 05, 2015 2:33 pm

Thanks Ivan
I get those kind of parts from old junk radios and TV,s so I have never seen one with only 2 pins as they usually use them just for filters.
I think a person could use a crystal the same way if a person could find one the right frequency.
You are right, RF circuits are really unstable if everything is not perfect. Thanks to you and Harry  I was able to zero in on my 
search coils and hit the frequency I was looking for within just a few cycles.  I look back to when I first came here and
I couldn't even get an oscillator to operate successfully. 



I have a new project now so it might be a while before I get back to that. I am restoring another old 70's Wurlitzer omni 6000 organ.
The old Lowery I restored is still working fine. It really had a lot of bad chips in it and was quite interesting to repair.  
I need a new service manual for it so I will posting more info on it in Harry's Wanted folder soon and maybe some one knows where I can find one.

Jalex2

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Re: Ceramic filter question

Post by Ivan on Sun Apr 05, 2015 9:41 am

Hi Jalex,
the second resonator, i.e. the filter is used to obtain a clean sinewave on the output.
Remember there are parasitic capacitances everywhere. They may be enough at 4,5 MHz, but too little at 455 KHz. 
Whether to ground the center pin of a filter used as a resonator, I am not sure. Try both possibilities.

BR from Ivan

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Re: Ceramic filter question

Post by Jalex2 on Sat Apr 04, 2015 2:45 pm

Hi
Ivan
Looking at the circuit you posted.  It shows two ceramic circuits. One is a Resonator and the other a filter. 
X1 and X2 in the schematic. The ones I am using are filters and they both have a center ground.
Could I leave off the ground and just connect the 100pf Caps at both ends like they did or does 
leaving the ground off hurt.
The other circuit that runs at 4.5 mhz does not have any capacitors and it works fine without them
It also has the center ground pin so it must be a filter too.

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Re: Ceramic filter question

Post by Jalex2 on Thu Apr 02, 2015 3:23 pm

Hi Ivan
I thought of that but I No I didn't use any capacitors as the 4.5 Mhz filter worked so well.
I did try a 470 Pf on one side of the 455 Khz but it stayed almost steady at 2.088 mhz.
I thought that those filters had two internal capacitors going to the center witch I have grounded.
I made a new search coil and it runs really good at 455 Khz with it's control set at center position.
I wanted to see if it changed it's performance in any way but it's pretty good already.

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Re: Ceramic filter question

Post by Ivan on Thu Apr 02, 2015 6:38 am

Hi Jalex,
did you use capacitors from both ends of the resonator to ground ? It should work, see e.g. here.
BR from Ivan

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Ceramic filter question

Post by Jalex2 on Wed Apr 01, 2015 8:39 pm

Hi
I put an 4.5 mhz filter across a cd4011 gate connected as an inverter with a 1 meg resistor as bios and got 4.5 mhz exactly.
I did the same with a 455 Khz AM filter and got 2.088 mhz on the counter. It seems like it's locked at some sort of harmonic but
I can't figure it. Has anyone got an idea on what might be wrong.?
I was playing with a metal detector circuit that works on 4.5 mhz and wanted to try it at a lower frequency.

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