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Re: Image question

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  • applewiz2000
    Hi Tom, A 1dB difference on some band or other (you don t say which you measured) is not unexpected. The amplitude difference varies across the 1 - 30MHz
    Message 1 of 17 , Jun 22, 2013
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      Hi Tom,

      A 1dB difference on some band or other (you don't say which you measured) is not unexpected. The amplitude difference varies across the 1 - 30MHz range.

      What you need to do is put in a pot to adjust your gain. Then use a sig gen at a mid HF (e.g. 15MHz) frequency to balance. You will find that above and below the balance drifts off though. While you are about it, reduce your overall gain on the SR V6.3 board. The stock gain is too high for modern sound cards.

      As to the image rejection of PSDR, the V2.5.x algorithm is better than the old V2 beta. But there is still the recurring bug where the rejection fails altogether after switching from Rx to Tx and back a few times.

      ~/Rob
      www.m0rzf.co.uk
    • tom
      Thanks Christos....EIA works great. Meanwhile I will look into why I have the difference between L and R... Tom
      Message 2 of 17 , Jun 22, 2013
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        Thanks Christos....EIA works great. Meanwhile I will look into why I
        have the difference between L and R...

        Tom

        On 6/22/2013 3:33 AM, sv1eia wrote:
        > Tom,
        >
        > Just some thoughts on your setup there.
        >
        > 1 dB is within the range but after all why not try to find the cause of imbalance and make it equal?
        > Also bear in mind that your rig might introduce some phase imbalance between I and Q which is not measured from ADCL/R (an o-scope is needed for that).
        > Try very short length cables between rig and audio card.
        >
        > If you use the quite old v1.12 then there is a "EIA" button which stands for "Effective Image Adjustment" that enables the image rejection algo, yet it takes some time to see results. There is a coefficient number besides the button that also needs tweaking, it goes from 0.00 to 1.00 and the larger numbers are giving faster results with lower image rejection, whereas smaller numbers give slower results with higher image rejection.
        >
        > 73,
        > Christos SV1EIA
        >
        >
        > --- In powersdr-iq@yahoogroups.com, tom <loeblt@...> wrote:
        >>
        >> Christos,
        >>
        >> I am using PSDR V12.X with RXTX V6.3 and Mobo. I have a 1db difference
        >> between left and right audio channels. My image rejection appears to be
        >> around 28DB. Does the 1db difference account for the poor image
        >> rejection? I assume there is no way for me to adjust the software for
        >> the difference in db.
        >>
        >> Thanks,
        >>
        >> Tom
        >>
        >
        >
        >
        >
        > ------------------------------------
        >
        > Yahoo! Groups Links
        >
        >
        >
        >
      • tom
        Hi Rob, Your amp is still humming away here and the 20 watts drives my SB220 to about 300 watts out. I saw some numbers on an old posting from Bob, g8voi, that
        Message 3 of 17 , Jun 22, 2013
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          Hi Rob,

          Your amp is still humming away here and the 20 watts drives my SB220 to
          about 300 watts out.

          I saw some numbers on an old posting from Bob, g8voi, that stated that
          even a .4 db difference in the channels can degrade the image rejection
          to the low 30 db range, so I was a bit concerned. I am somewhere around
          25 db rejection at the moment.

          I thought perhaps I could insert a small pad in one channel to equalize
          the audio between the SR and the PC audio card rather than tearing into
          the Softrock but that may wind up being the only option.

          As Christos suggested, the PSDR V12.20 EIA button seems to work very
          well for me at the moment.

          Tom

          On 6/22/2013 10:04 AM, applewiz2000 wrote:
          > Hi Tom,
          >
          > A 1dB difference on some band or other (you don't say which you measured) is not unexpected. The amplitude difference varies across the 1 - 30MHz range.
          >
          > What you need to do is put in a pot to adjust your gain. Then use a sig gen at a mid HF (e.g. 15MHz) frequency to balance. You will find that above and below the balance drifts off though. While you are about it, reduce your overall gain on the SR V6.3 board. The stock gain is too high for modern sound cards.
          >
          > As to the image rejection of PSDR, the V2.5.x algorithm is better than the old V2 beta. But there is still the recurring bug where the rejection fails altogether after switching from Rx to Tx and back a few times.
          >
          > ~/Rob
          > www.m0rzf.co.uk
          >
          >
          >
          >
          > ------------------------------------
          >
          > Yahoo! Groups Links
          >
          >
          >
          >
        • applewiz2000
          Hi Tom,, I don t think 0.4dB will make any difference. The algorithm (not that I have detailed knowledge of it) should be able to cope with small amounts of
          Message 4 of 17 , Jun 23, 2013
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            Hi Tom,,

            I don't think 0.4dB will make any difference. The algorithm (not that I have detailed knowledge of it) should be able to cope with small amounts of imbalance as one of it's major "raisons de etre".

            It's a fair bet that the Flexradios do not always have <0.3dB amplitude match between I/Q channels across all HF bands.

            I have not used PSDR-IQ V1.12 for years. The V2.5.2 version gets >40dB most of the time. Only Christos can really answer how good relatively the 1.12 rejection algorithm is compared to V2.5.x.

            Excellent to see a product I designed in good use. Time will tell if the Mitsubishi RD16HHF FETs outlast the Heathkit SB220 !!

            73s, Rob.


            --- In powersdr-iq@yahoogroups.com, tom <loeblt@...> wrote:
            > Hi Rob,
            >
            > Your amp is still humming away here and the 20 watts drives my SB220 to
            > about 300 watts out.
            >
            > I saw some numbers on an old posting from Bob, g8voi, that stated that
            > even a .4 db difference in the channels can degrade the image rejection
            > to the low 30 db range, so I was a bit concerned. I am somewhere around
            > 25 db rejection at the moment.
            >
            > I thought perhaps I could insert a small pad in one channel to equalize
            > the audio between the SR and the PC audio card rather than tearing into
            > the Softrock but that may wind up being the only option.
            >
            > As Christos suggested, the PSDR V12.20 EIA button seems to work very
            > well for me at the moment.
            >
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