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ExtIO_sddc HDSDR FAQ

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Oscar Steila edited this page Dec 28, 2020 · 3 revisions

#114 I want to use the bandwidth edges correctly in LW MW, I have to set lower the Local Oscillator (LO) even to see the frequencies. Why?

If you select the 16 MHz bandwidth and you set the LO to 7MHz you get the full spectrum like this. 16 MHz sample rate with 7MHz LO While if you set the LO at 8MHz you get the following situation. 16 MHZ sample rate with 8MHz LO The tuning of a 999 KHz station is still possible but the LW band is filtered out by the bandpass filter cutoff. Every sample rate uses a bandpass filter centered on the LO position. It filters out the edges of the SR band to avoid alias of out of band signals.

A procedure to receive full LW MW band:

  • Set the sample rate to 4 MHz , the reason is that the band filter has not a sharp cutoff so 2 MHz gives a useful bandwidth that is narrow for a 0-2 MHz span.
  • Tune LO display to 1 MHz and lock it (The locking of LO is done moving the mouse on LO label left of display and clicking right button of mouse).
  • Move the zoom control of HDSDR to see spectrum from 0 to 2MHz. https://sdr-prototypes.blogspot.com/2020/12/extiosddcdll-v11-rc1.html
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