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Re: [powersdr-iq] Re: Image question

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  • 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 1 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 2 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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