Question about ceramic resonator again.

[RCinFLA]

Look at the ceramic filter catalog for Murata at:

PDF Catalog | Filters for Communication Equipment | Murata Manufacturing Co., Ltd.


Toko at:
**broken link removed**

 

[Warpspeed]

Your best bet might be to just build a conventional IF amplifier using the usual 455Khz double slug tuned coupling transformers for the first stage. This will not be sharp enough, but it will readily eliminate all the out of band frequencies. Then use the 455Khz ceramic filter as a second stage to really sharpen up the skirt selectivity.

 

[Space Varmint]

Cool cool! Got to check that out. And nice test config. Bob! Well, I might have to take some stuff back. I got two of these cheap ceramics in there with an amp in between and I'm getting some good performance right now! The selectivity is not bad with the skirt of one cutting off some bandpass of another. The dawg gone thing is starting to impress me. It's doing every bit what my Icom 745 is doing and it has an outside antenna. I might build a BFO for it. I think I might have had too much rf front end gain before. It's working right now.

edit*
Oh yeah I changed the front end filter a little too. Maybe some IF was getting back into the front end. Right now it has no shielding and it's doing a bang up job for short-wave. I'm kinda psyched!

 

[BobW]

You can also cascade two ceramic filters to get better performance. Two 4 pole filters essentially become an 8 pole filter. You get more insertion loss, but you can make up for it with a bit more gain in your IF amp.

 

[teutonic]

getting back to ceramic resonators and a query of my own ..

I want to make a 1MHz sine wave osc. I could'nt get 1MHz crystals ( uk ) but got a couple of 1MHz ceramic resonators.

Q1.. Can I just drop a two pin 1MHz ceramic resonator in place of a quartz xtal as a direct swoput in any given oscillator circuit.

Q2 - I read on the internet if using 2 pin ceramic resonators a 22 pF capacitor has to go from resonator input to gnd and resonator output to ground. Is this .... an absolute? Should'nt that value need changing depending on circuit / freq. used etc ?

cheers all

 

[BobW]

1. Yes, just drop in the resonator in place of the crystal. See my diagram several posts above. It uses a ceramic resonator for the oscillator. The oscillator is on the left side of the diagram.

2. The value of the capacitor is normally specified by the resonator manufacturer. 22 pF is typical. By replacing one of them with a trimmer, you can fine tune the frequency.

 

[Space Varmint]

1. Yes, just drop in the resonator in place of the crystal. See my diagram several posts above. It uses a ceramic resonator for the oscillator. The oscillator is on the left side of the diagram.

2. The value of the capacitor is normally specified by the resonator manufacturer. 22 pF is typical. By replacing one of them with a trimmer, you can fine tune the frequency.

Could you please post it?

 

[Space Varmint]

On your data sheet about the 20pf cap. Usually since it is going to ground (parallel) it means that the resonator you are using has about 20ph series capacitance internally and so the external cap is used to cancel it out but yes the PCB will effect the value as well, so you may need to use a different value like 40 pf etc.

 

[BobW]

Could you please post it?

The diagram?
Just scroll up the window to my April 29 post. That's the schematic I was referring to. If you need other info, let me know.

 

[Space Varmint]

Oh, silly me. I did not know you were referring to that one. Anyway, got a hot little formula here I have done in my little spare time which I carved out for this. I just finished the AGC so I can ram rod the signals through it...lol.

 

[Mikebits]

I thought most ceramic resonators had built in load capacitors thus eliminating the need for external ones. One of the selling points for resonators is reduced parts count and cost. Of course stability and accuracy is the trade off.

 

[Space Varmint]

I thought most ceramic resonators had built in load capacitors thus eliminating the need for external ones. One of the selling points for resonators is reduced parts count and cost. Of course stability and accuracy is the trade off.

Well 20pf is not that much. I did not need any for this one but I had to buffer the output and make sure I had enough input drive.

 

[Space Varmint]

Alright! The AGC fixed that problem with the IF harmonics. It's all one frequency now with no instance of any other frequency. I hopped up the rf front end gain and the post mixer amp and I get all the goodies now. Listening to David J Smith right now on 7.315MHz. Great signal!

 

[BobW]

I thought most ceramic resonators had built in load capacitors thus eliminating the need for external ones. One of the selling points for resonators is reduced parts count and cost. Of course stability and accuracy is the trade off.

The 3-terminal resonators (not to be confused with filters) have the capacitors built-in. The 2-terminal resonators don't. Typically the low frequency resonators (under 1 MHz) are 2-terminal devices and don't have the capacitors. I think it's probably because the low frequency ones need bigger caps which are harder to incorporate into the package. The 455 kHz resonator that I used in my oscillator cct. requires 100pF. I was actually surprised that Space Varmint's 455 kHz resonator only requires 20pF.

 

[Mikebits]

I do see from the Murata catalog that the resonators can be ordered with or without the internal load capacitors depending on the part number. For project builds of one to a few, I would stay with the higher end quartz products, but that is just a design choice.

 

[Space Varmint]

The 3-terminal resonators (not to be confused with filters) have the capacitors built-in. The 2-terminal resonators don't. Typically the low frequency resonators (under 1 MHz) are 2-terminal devices and don't have the capacitors. I think it's probably because the low frequency ones need bigger caps which are harder to incorporate into the package. The 455 kHz resonator that I used in my oscillator cct. requires 100pF. I was actually surprised that Space Varmint's 455 kHz resonator only requires 20pF.

Actually I'm not using one at all right now. I must have it in the circuits because I am using two resonators for sharper response. I better sweep them so that if I make more I get the same performance. I'm thinking about doing a kit with it because it needs no shielding.

 

[Space Varmint]

How important is the local oscillator signal? I know that is a loaded question but what all should one be looking for? I have some ARRL Handbooks and for the most part they just discuss "DB" level. There is allot more to it than that I am sure. I will look inside various ports of the mixer section and notice that the frequency will fold over (double) at some range or ranges of frequency. Moving the tap on my Hartley oscillator (VFO) will cause changes, sometimes for the better. But in building many of these things I have noticed also that amplifying the signal usually decreases receiver performance in that it appears to be less sensitive. I am not sure what that condition is.?? So what I come up with is the core material seems to have the greatest effect on the sensitivity and not necessarily the gain of the front end. It appears to be the phase angle of the VFO. Make sense? Now Mike will disagree with me here and I do respect his opinion because the guy knows his stuff in radio. But I think the VFO level is the best way to control intermod. It seems the higher the level the better IMD suppression. But also trying to get too much gain out of the front end will do that too.

 

[Mikebits]

It seems the higher the level the better IMD suppression.

Well I actually agree with that. But remember there is typically an optimum drive level and once exceeded performance will then degrade. I found an article that discusses LO drive level in double balance mixers.
Double balanced mixer tutorial :: Radio-Electronics.Com