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op amp voltage drop ensemble rx

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  • millerchris75
    Thank you for the help on a post from a weekend ago with image rejection problem. I still have image rejection issues but I think the reason is I am not
    Message 1 of 2 , Mar 30, 2013
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      Thank you for the help on a post from a weekend ago with image rejection problem. I still have image rejection issues but I think the reason is I am not getting the I (left side input). Using hdsrd and moving the channel line input the left side (I) is about 3-4 dB less. It is 4 dB less but the signal from mfg 269 is still on, connected to ant input, at 7.175MHz, there but extremely weak. Q channel is good.
      It follows the ensemble inputs, not cables.

      When I run the 10k ground to hair pin R31 OP Amp test, the 2.5v DROPs to 2.1v, which also drops the output of other side of the op amp. Both channels have 2.5v without 10k. Performing this test to the R30 pin, other op amp side, the voltage goes 2.6v to 3.94v just as it should. I have traced the T3, looks good, and all Rs in op amp areas check out prior to soldering and after soldering. Why would op amp V drop when the 10k is applied to R31? I do not see any loading issue with components C21 or R31, no solder splatter. Is this an indication of input 2 side of op amp? Which looks like this is the I signal. Any ideas? Thanks Chris
    • Alan
      ... Subject: [softrock40] op amp voltage drop ensemble rx ... I do not understand what you are seeing. On HDSDR spectrum are signals exactly the same each
      Message 2 of 2 , Mar 31, 2013
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        ----- Original Message -----
        Subject: [softrock40] op amp voltage drop ensemble rx


        > Thank you for the help on a post from a weekend ago with image rejection problem. I still have image rejection issues but I think
        > the reason is I am not getting the I (left side input). Using hdsrd and moving the channel line input the left side (I) is about
        > 3-4 dB less. It is 4 dB less but the signal from mfg 269 is still on, connected to ant input, at 7.175MHz, there but extremely
        > weak. Q channel is good.
        > It follows the ensemble inputs, not cables.
        >

        I do not understand what you are seeing.

        On HDSDR spectrum are signals exactly the same each side?
        Is there absolutely no difference?
        What is 4dB less? How do you get this measurement? Input channel mode?
        How does it compare with the pictures here https://sites.google.com/site/g4zfqradio/hdsdr-iq-balance ?
        Do the sliders make any difference?
        Just say left/right either could be I or Q depending on the jumpers.
        But look at the IC first.


        > When I run the 10k ground to hair pin R31 OP Amp test, the 2.5v DROPs to 2.1v, which also drops the output of other side of the op
        > amp. Both channels have 2.5v without 10k. Performing this test to the R30 pin, other op amp side, the voltage goes 2.6v to 3.94v
        > just as it should. I have traced the T3, looks good, and all Rs in op amp areas check out prior to soldering and after soldering.
        > Why would op amp V drop when the 10k is applied to R31? I do not see any loading issue with components C21 or R31, no solder
        > splatter. Is this an indication of input 2 side of op amp? Which looks like this is the I signal.

        So when you bridge R31 to ground the voltage at R33 goes lower?
        This should not happen.
        Check soldering.
        Does pin 3 remain at 2V5?

        73 Alan G4ZFQ
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