AGC in superherodyne FSK receiver

[7rots51]

superherodyne receive+agc

Hi

In a superherodyne FSK receiver with 1MSPS and with using SA639 in IF section
Is it necessary to use AGC after first mixer to limit signal power for SAW filter in IF1?

 

[vfone]

No

 

[7rots51]

how to adjust the gain of LNA,IF1 Amp to prevent stress on SAW filter?
(SAW Filter at IF1 accept maximum 0dbm)

How to assign gain values?

 

[LvW]

No

An answer as short as possible. But: Is it also as clear as possible ?
(some days ago I have asked all guys in this forum not to use only one word or only one abbreviation as name of a topic and to describe the problem in detail; may be I should extend my desire also to people who give answers).

 

[flatulent]

You use limiter stages. The one before the filter set at a level to prevent damage and the ones after the filter to make sure the demodulator is within its range. Have enough gain so that the noise is within the demodulator range.

When you get a strong signal the limiters will push the noise down.

 

[vfone]

No

An answer as short as possible. But: Is it also as clear as possible ?
(some days ago I have asked all guys in this forum not to use only one word or only one abbreviation as name of a topic and to describe the problem in detail; may be I should extend my desire also to people who give answers).

1. The first question of the post didn’t specify that is looking for a detailed answer (only the second question was looking for this)
2. I am following ONLY the rules imposed by this forum, and not the rules imposed by the members.

@ 7rots51
On the top of what flatulent mentioned, if the level at the SAW filter is too high, I would propose a switched LNA. Could be a 3 stages switching: High-Gain, Low-Gain and By-Passed, method that sometimes is used in 3G receivers.

 

[7rots51]

You use limiter stages

How to design limiter stages?any reference?any RFIC,MMIC for this?

 

[Borber]

You can use diode BAT14-099 in antiparallel connection across SAW input.