Sa636 receiver stability issue

Good afternoon,

I'm using a SA636 (http://www.nxp.com/documents/data_sheet/SA636.pdf) as a direct conversion receiver. I bypassed the down-conversion mixer and connected the received signal (BFSK centered in 10.7MHz) to the IF amplifier using a RF FET as a buffer. The RSSI indicator is a little bit high when there is no signal in the receiver. I think i have some stability problem, but i cannot figure it out. What can be the problem? I just have to explain the possible reasons for that, for now i don't need to solve the problem.

I hope you can help me with this.

Thank you in advance

Humberto Castanheira

higher RSSI than expected is an indication of poor S/N ratio. Check for conducted and radiated noise.
LO noise or signal noise. vs drive levels verify with coax to SA.
PS noise. Consider ferrite and low ESR caps at operating f.

Good luck.

If you share all the assumptions in your design, we will not have to guess?

Is the LO high output well isolated from the Rf input? any crosstalk with positive feedback will get regenerative feedback,.. i.e. oscillations in RF input. so should your sections to isolate the region of crosstalk.

The better your design description, the better understanding people can have. What is your RSSI level?