RF analog low-pass filter basics

[booblik]

Hi all,

I'm starting on RF design and have a very basic question.

I have a signal 433MHz with a ~1MHz baseband. When receiving the signal, should the RF filter after the antenna have a bandpass filter with the stopband frequencies at 432 and 434, or a low-pass filter at 0 - 1MHz?

 

[Malek Lamari]

The RF-Filter should be centered at the signal center frequency witch is in your case 433, so the band-pass will be between 434-432.
0-1 filter goes true, if you place the filter after the down-converter mixer in case of direct conversion receiver (zero IF).

 

[volker_muehlhaus]

a bandpass filter with the stopband frequencies at 432 and 434

This narrow band pass is difficult to implement. In downconverting receivers, a wide band pass is used in the input section and the narrow band pass is placed behind the mixer. At that frequency, the relative bandwith is much less of a problem.