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

[Tachwali, Yahia]

OK, It is clear now. Thank you very much to all.

Kind regards,
Yahia Tachwali
________________________________________
From: address@hidden address@hidden on behalf of Marcus D. Leech address@hidden
Sent: Tuesday, March 29, 2011 3:47 PM
To: address@hidden
Subject: Re: [Discuss-gnuradio] IF Frequency of WBX board

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



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