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[Discuss-gnuradio] Re: Re: Frequency shift in the received and generated
From: |
Bruhtesfa Ebrahim |
Subject: |
[Discuss-gnuradio] Re: Re: Frequency shift in the received and generated signals of the USRP |
Date: |
Thu, 20 Nov 2008 19:54:31 +0100 |
> 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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