How the crystals for 200MHz crystal filter?

[asrock70]

Can you recommend crystals suitable for design crystal filter 200MHz (4th - 7th) ?
What is the difference in calculating the filltr on first harmonics or 3th, 5th overtone?

 

[goldsmith]

Hi asrock !
Is your mean kind of active filter or just passive ?
Best Wishes
Goldsmith

 

[asrock70]

I thing passive filter

 

[goldsmith]

If it was active filter i had better ideas . but for passive filter i haven't any experience . but i can tell you some things that are coming through my mind :
each crystal can work in over tone resonances . (3rd ,5th ,7th ... ) but the amplitude will be lower . a friend of mine told me if you use a tuned circuit that selected for one of the over tone frequencies , the crystal will guarantee it's precision ! but i don't know how much it can be correct ! it is all i can say regarding passive filters with crystal because i have not any experience in this case but if it was active i could tell you better things .
Good luck
Goldsmith

 

[asrock70]

My first idea is passive filter 4-5th order and integrated transistor amplifier ERA 5
**broken link removed**
For design I use http://sq2gxo.wordpress.com/2010/04/05/crystal-ladder-filters-i-software/

 

[sky_123]

I've never had to design a xtal filter from individual xtals, but I believe it's quite hard, without being able to characterise the xtals, and that is not easy (need to build a test jig for that).
Also, 200MHz implies that you can get 200MHz xtals (it is possible). I think SAW filters are more prevalent at higher freqs.
Why do you need such a sharp filter at this strange freq?
Normally people mix to a defined freq (e.g. 45MHz) and employ ready-made filters which are readily available at those freqs.

 

[asrock70]

200MHz crystal with 200MHz on 1 overtone is technically possible, but cost very expensive solution, therefore used for high frequency crystal, and the third or fifth over tone (66.6666MHz or 40MHz)
Crystals, it should be measure and thus probably also choose to be as similar as possible, this is no big problem I have vector analyzer

 

[goldsmith]

Hi again . i have seen a good circuit in an RF design book which was Crystal gate . it consists 6 crystals . if you are interested i can attach it here .
Regards
Goldsmith