Re: [Discuss-gnuradio] IF Frequency of WBX board

[Marcus D. Leech]

On 03/29/2011 11:29 AM, Tachwali, Yahia wrote:
> Hello Josh,
>
> Thank you very much for the reply. It seems to me that these functions are 
> generic and not WBX specific. If I understood you correctly, WBX board does not 
> have a fixed IF frequency. I had some experience with other SDR platforms where 
> their RF boards have fixed IF frequencies at 30 MHz (Super-heterodyne 
> receiver). This is not the case for WBX board?
>
> Kind regards,
> Yahia Tachwali
All boards except for the original TV_RX use a Zero-IF architecture, 
wherever possible.  Sometimes, however, the coarseness of the PLL
  synthesizer on the RF cards requires a little bit of "clean up", so 
that the final stage of down-conversion is done in the FPGA to convert your
  desired center frequency to DC.  For example, if the PLL synthesizer 
can only "tune" in 25KHz steps, and you've asked for a frequency
  that isn't a multiple of 25KHz, the cooperation between UHD, the FPGA 
seeks to make sure that your baseband DC frequency is precisely
  (within 1Hz, and subject to the accuracy of the master clock) where 
you expect it to be.


The TV_RX used an IF at (if I recall correctly) 5.75MHz, which was 
down-converted inside the FPGA to DC.  I think the new TV_RX2 uses
  a Zero-IF architecture, but I'm happy to be corrected on this.

The Zero-IF or direct-conversion approach has distinct benefits over a 
superheterodyne approach, although it does require a
  complex (I and Q) "format" in order to make it work correctly.

--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org