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39244Re: LO Question

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  • g8voip
    Jan 2, 2010
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      Hi Tom,

      Those LO frequencies seem to be pretty close to the programmed values. The differences are due to the tolerance of the Si570 master oscillator.

      The PIC software makes the assumption that the Si570 is running at the default 114.285MHz, where in practice there will be some small error.

      You need to carry out a calibration within Rocky to update the correction factor stored in the Rocky.ini file.

      As you are essentially using a 'fixed' frequency LO, all you need to do is go to the 'Tools' menu and select 'Si570 Calibration'. You will see there is a box to enter the 'true' frequency you are tuned to. Hopefully once you have updated that, the 'dial' frequency will tie up with what you expected.

      If you are not aware, as you have a dual band radio, select 'Multi-band' on the set up DSP tab, and then edit the Rocky.ini file to add all of your centre frequencies. When you run Rocky, you can now select the centre frequency from the pull down to the right of the frequency display. Makes changing bands a lot easier.

      It sounds like you have not optimised the image rejection, hence seeing images each side of the centre frequency. From the 'Tools' menu item, select 'RX I/Q balance'. Make sure both 'Collect Data' and Correct Balance' are checked. Best to do a reset, then the correction curves will gradually build up automatically, or if you have a signal generator, you can speed up the process by stepping a signal across the band and pausing at each step. You should see the 'image' automatically being reduced.

      If that process fails, make sure you have both the I and Q signals being output from the receiver through to the PC. You can see the relative values for the two channels on the bottom line of the Rocky display. Disconnecting either the I or Q, will remove any image rejection present.

      73, Bob G8VOI
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