Ceramic filters

[Space Varmint]

I bought a bag of cheap 455KHz ceramic filters. I could not get a data sheet because Digi-Key discontinued them. It has 3 pins. I assumed the center pin is ground. Anyway I could not get it to work worth a crap. Anyone have familiarity with these? I mean all my original frequencies pass right through the thing. I have a mechanical 455KHz filter that came out of a Collins transceiver but it is huge. I might try making a crystal filter from the crystals I have. Is 10.240 Mhz a good one? I mean one of the standards? I don't hear anything there.

 

[Space Varmint]

Sure wish I could get this ceramic filter to work right. Nobody has experience with t don't like having all my frequencies pass through. I just have no idea how to hook it up. Should I have some capacitance to ground or something. I don't know the impedance and I cannot find anything about them on the internet. The Digi-key part number is #TK2331-ND but they discontinued it and have no data sheet.

 

[Mikebits]

See if this data sheet helps. **broken link removed**

At any rate, the filter is a Toko part so you may contact them. Question, how have you determined all frequencies are passing through, do you have a spectrum analyzer?

 

[Space Varmint]

See if this data sheet helps. **broken link removed**

At any rate, the filter is a Toko part so you may contact them. Question, how have you determined all frequencies are passing through, do you have a spectrum analyzer?

Oh thanks Mike! Yeah I went to their website and played hell trying to find the data sheet. On the frequencies? They are all there on the scope. I mean it's like a short. No impedance at all. I wonder if the thing works.

edit*

OK, 3K series and 3K parallel out with 50pf in parallel. I had the pins right though I tried every combination later.

 

[Space Varmint]

Wow wow wow! Thanks again Mike. Now I need to get the right balance in my rf front end gain and the mixer gain (using 3904) and should be a keeper. I did need to increase the drive. I think the series resistor is what did the trick because I tried caps to ground on both sides and resistors but never used a series resistor. Guess that is to dampen the impedance. Had the post mixer amp been the same as the input impedance, I would never have known about the resistor.

 

[Mikebits]

deleted post...

 

[Space Varmint]

Really it doesn't need to be. Yeah, I need the extra drive but when I do I get high frequency parasitics on the new frequency. Probably a shielding problem. So what happens is. I pick up the signals great as long as the direct conversion signal passes through the filter. When I increase the drive I loose information. I get no signals except for one or two local AM broadcasts. And even they are real muddy. I'm just not sure if it's possible to pull off this single conversion without shielding which was my goal.

What do you think Mike? In the commercial low end (very low end) receivers they usually use those shielded IF transformers. That's probably the only way around it maybe?