f***i
发帖数: 33 | 1 我是搞物理的，对RF 电路不熟，想请教EE的达人们如何做一个high Q crystal filter:
我现在需要将一个noisy and jittering RF 信号（@25.320MHz）通过一个high
quality factor RF filter.通常crystal filter 是具有比较高的Q>10^4, 相比
ceramic filter or LRC filter. 现在在digikey 和Mouser 上查到的crystal Filter
都是固定频率的，最接近的是25.0MHz. 有什么办法自己做一个crystal filter 在25.
320MHz(Q>10^4)吗？ 还有就是我的信号是50 Ohmn BNC coax 上的，自己搭crystal
filter怎么考虑输入端和输出端的Impedance match?
谢谢大家了！兔年吉祥！ | g*z
发帖数: 124 | 2 you need custom crystals, which could be expensive.
usually crystal can have 50ppm offset, which means for 25M crystal, the
offset frequency can be up to 1250Hz, still far away from your 25.320MHz
requirement. | f***i
发帖数: 33 | 3 can I use another capacitor in parallel with the crystal to tune the
resonance frequency(pass frequency)?
I am wondering whether this will effect the quality factor of combined
filter(crystal filter+additional capacitor) or not?
thanks.
【在 g*z 的大作中提到】
: you need custom crystals, which could be expensive.
: usually crystal can have 50ppm offset, which means for 25M crystal, the
: offset frequency can be up to 1250Hz, still far away from your 25.320MHz
: requirement.
| g*z
发帖数: 124 | 4 cap can be used to tune crystal, however the pulling range is very limited,
for example, 100ppm, which is just a few khz off the 25MHz frequency.
note that high Q stuff like crystal has very narrow bandwidth, less than
50Khz for a 25MHz crystal, so forget about tuning, get custom made crystals. |
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