[Discuss-gnuradio] Re: Re: Frequency shift in the received and generated signals of the USRP

[Bruhtesfa Ebrahim]

> Tuning is done to the best of the receiver's (synthesizer/PLL)
> ability.  Please reference what a superheterodyne receiver is:
> 
>     http://en.wikipedia.org/wiki/Superheterodyne
> 
> Now, knowing that there is a 64MHz local oscillator reference on the
> board, that must somehow get "multiplied up" using a PLL to generate
> your 2.4GHz signal.  Some simple math follows:
> 
>     Multiplier = 2.4e9 / 64e6
>     Multiplier = 37.5
> 
> So a 64MHz signal must be multiplied up by 37.5x to generate the
> desired frequency.  Now, lets imagine that our crystal oscillator is
> off by 320Hz.  I believe this is a crystal oscillator rating of 5ppm.
> For more information on PPM, see:
> 
>     http://en.wikipedia.org/wiki/Parts_per_million
> 
> Establishing we have an oscillator with a 5ppm offset, and a
> multiplier of 37.5, we can then calculate what our frequency offset
> will be:
> 
>     Foffset = multiplier * LOoffset
>     Foffset = 37.5 * 320Hz
>     Foffset = 12kHz
> 
> By only being off by 5 cycles for every 64 million, we have created a
> 12kHz offset only at the transmitter.  This may be added or subtracted
> based on how the receiver is sampling as well.


Thanks again!

Actually, the major problem for me was there is no data sheet/manual 
about the XCVR2450 tranceiver. The only information on the manufacturer 
website, www.ettus.com , is the operating frequency range and the 
maximum transmit power. So, i didn't know to what IF frequency the 
tranceiver downconverts the RF signal;how much gain it provides and to 
what extent the oscillator of the XCVR2450 is accurate.

So Dear : Matt Ettus,

Do you have any data sheet, description or manual for this tranceiver ? 
If yes, where can i get it? If no, I think it is really important to 
prepare a data sheet and a manual for each USRP Daughterboards; 
otherwise, users of your daughterboards will face the same problem in 
the future.


Bruhtesfa


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