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AD9361 AGC Fast attack mode won't unlock

Question asked by epiq-mj on Jan 27, 2016
Latest reply on Mar 25, 2016 by tlili

I have enabled the AD9361 in Fast Attack AGC mode per the example from the "AD9361 Gain Control and RSSI User Guide" v2.8

 

I am using a signal generator to input short signals. Specifically this is an LTE uplink Random Access Preamble, approxmiately 1ms long. The AGC works well at reducing the gain to accomodate high strength signals, but never seems to unlock. The gain never goes back up, and low strength signals are no longer detected.

 

Edit: I've used the output from control register 0x35 to verify that the AGC remains in state 5 after the signal is turned off. Here is the AD9361 register configuration I used.

    0x0FB, 0x08
    0x0FC, 0x23
    0x0FD, 0x4C
    0x0FE, 0x44
    0x100, 0x6F
    0x101, 0x0A
    0x103, 0x08
    0x104, 0x2F
    0x105, 0x3A
    0x106, 0x22
    0x107, 0x2B
    0x108, 0x31
    0x111, 0x0A
    0x11A, 0x1C
    0x120, 0x0C
    0x121, 0x44
    0x122, 0x44
    0x123, 0x11
    0x124, 0xF5
    0x125, 0x3B
    0x128, 0x03
    0x129, 0x56
    0x12A, 0x22

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