mydreamhouse wrote on Feb 24th, 2009, 8:35am:the IF frequency is about 180MHZ,and followed by external LC BPF.
mydreamhouse wrote on Feb 27th, 2009, 2:58am:who can give me some advice?
Your question is too lack of information, so no one can answer.This is very true for all your posts too.http://www.designers-guide.org/Forum/YaBB.pl?num=1235494642/0#0http://www.designers-guide.org/Forum/YaBB.pl?num=1229879167/0#0If you want someone to answer your post, you have to describe your questions regarding situation and condition in detail using industrial standard terminologies.mydreamhouse wrote on Feb 24th, 2009, 8:35am:as i known, the IF LC BPF must be match with IF input stage,but i don't know how to design it.
If your system is very narrow band system, you can use simple resonator as BPF here high impedance of next input stage is required.
Here you might be able to use impedance of next input as part of BPF.
Even though you design formal filters, there are three variations,
(1) R-R Type
(2) R-infinite Type
(3) 0-R Type
You seem to know only (1).
And for BPF design, resonator coupled structure is preferable than formal filter design.