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7rots51
Joined: 17 May 2002
Posts: 1261
Helped: 14
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 08 Jul 2008 16:34 AGC in superherodyne FSK receiver |
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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?
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vfone
Joined: 10 Oct 2001
Posts: 1674
Helped: 209
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| 08 Jul 2008 18:47 Re: AGC in superherodyne FSK receiver |
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| No
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7rots51
Joined: 17 May 2002
Posts: 1261
Helped: 14
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| 08 Jul 2008 20:05 Re: AGC in superherodyne FSK receiver |
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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?
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LvW
Joined: 07 May 2008
Posts: 683
Helped: 128
Location: Germany
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| 08 Jul 2008 20:44 Re: AGC in superherodyne FSK receiver |
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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).
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flatulent
Joined: 19 Jul 2002
Posts: 4860
Helped: 288
Location: Middle Earth
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| 08 Jul 2008 20:49 Re: AGC in superherodyne FSK receiver |
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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.
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vfone
Joined: 10 Oct 2001
Posts: 1674
Helped: 209
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| 09 Jul 2008 10:10 Re: AGC in superherodyne FSK receiver |
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| LvW wrote: |
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.
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7rots51
Joined: 17 May 2002
Posts: 1261
Helped: 14
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| 09 Jul 2008 13:51 Re: AGC in superherodyne FSK receiver |
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| Quote: |
| You use limiter stages |
How to design limiter stages?any reference?any RFIC,MMIC for this?
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Borber
Joined: 01 Jan 1970
Posts: 1454
Helped: 109
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| 09 Jul 2008 16:26 Re: AGC in superherodyne FSK receiver |
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| You can use diode BAT14-099 in antiparallel connection across SAW input.
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