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Custom Zoom Level

I've had a surf through the forum discussions to see if anyone had breached the topic of setting different frequency widths for corresponding zoom levels but couldn't find anything obvious. What I would like to do is set the frequency width for example to about 155kHz for a particular zoom setting, say WF7 or WF8 so that it encompasses a particular band that I'm interested in viewing rather than the current widths of 234kHz (WF7) or 117kHz (WF8).

If anyone has any idea if this could be achieved then I'd be very grateful for such information.

Comments

  • jksjks
    edited June 2019
    For the waterfall/spectrum the decimation of the CIC filters inside the FPGA are powers-of-two. So given the value of the ADC clock you get bandwidths of z0 = 30 MHz, z1 = 15 MHz, z2 = 7.5 MHz, ... z7 = 234.4 kHz, z8 = 117.2 kHz, ... z14 = 1.8 kHz (30 MHz is a slight simplification given the 66.666600 MHz nominal ADC clock and explains why there is a 30/32 MHz selectable max frequency mode on the admin page).

    In theory the CIC decimation value can be any integer number. For example for the audio two stages of CIC are used with decimation factors of 505 and 11 in the case of 12 kHz audio bandwidth. But changing the waterfall CICs from their existing design would take a tremendous amount of work. The associated C code on the Beagle controlling the waterfall would also have to change.

    An alternative is to take the FFT result from the z7/234 kHz spectrum, throw away bins and remap the remaining 155 kHz of spectrum across the width of the display. You would have lower resolution of course.
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