Hi,
1) See :
http://gnuradio.org/trac/wiki/UsrpFAQ
http://gnuradio.org/trac/wiki/UsrpFAQ/Clocking
http://gnuradio.org/trac/wiki/UsrpFAQ/Gen
2) To make nearly 0 Hz frequency shift between your TX and RX you have to use a third device Spectrum analyzer or third USRP (no need to warry about its calibration since the error will be the same for both) as follows:
a) Start transmitting single tone from TX USRP (using usrp_siggen.py)
b) Observe and record spectrum analyzer received tone frequency.
c) Stop TX USRP.
d) Start transmitting single tone from your RX USRP (using usrp_siggen.py).
e) Observe spectrum analyzer received tone frequency. Adjust your transmitting frequency from your RX USRP until you get exactly the same value found in step-b
3) I appolagize about my previous post so
many spelling errors!.
Regards to all,
Firas
--- On Thu, 7/24/08, kaleem ahmad <address@hidden> wrote:
From: kaleem ahmad <address@hidden>
Subject: Re: [Discuss-gnuradio] FSK with RFX2400
To: address@hidden
Date: Thursday, July 24, 2008, 5:07 PM
Hi,
Can some one explain in a little bit detail about where is the clock or
oscillator (on daughter board or on mother board) and how much is its
resulution for RFX2400 daughter board.
I tried to solve the problem of frequency mismatching by calculating the
frequency shift at receiver end by using usrp_fft.py and then by
adding/subtracting that frequency from RX USRP frequency as explained by
Firas and Patrick. But it dont solve the problem although it improves the
quality of data
but because of this effort at least I understand that the
problem is really some where because of frequency mismatching.
So it will be helpful for me if some one either give some good document of
USRP explaining clock/oscillator or just explaing the fuctionality of it by
him/her self.
Thanks
Firas A. wrote:
>
> Hi Kaleem,
>
> Each USRP has its on reference crystal oscillator. This oscillator may
> have maximum +/- 50 PPM ( Matt said the new USRPs has maximum 20 PPM)
> frequency error. Lets assume the error is 10 PPM in each USRP. This means,
> that at 2500 MHz (2.5 GHz) the error = 2500 * 10 = 25000 Hz = 25KHz.
>
> Now imagine that the first USRP has +25 KHz frequency deviation error and
> the second one has - 25KHz frequency error. This means + 50 KHz frequency
> mismtch between your TX and Rx Frequencies. This is probably what is
>
causing this high error rate that you see.
>
> To solve this problem you simply do :
>
> 1) Use usrp_siggen.py to send single tone at F1 frequency (For example,
> use F1 = 2475 MHz) from your TX USRP. The best thing is F1 be the
> frequency used in your FSK experiments.
>
> 2) With your RX USRP, start usrp_fft.py with frequency F1 and decimation=
> 128 (or 256). You should see your transmitted tone but may be it's
> frequency is shifted. Calculate this frequency shift.
>
> 3) Add/subtract this frequency shift to your RX USRP frequency tunning
> function.
>
> 4) Now your two USRPs frequency mismatch should not be the problem. If the
> errors is still there, then you have to search for another reason.
>
> Regards,
>
> Firas
>
>
>
> --- On Wed, 7/23/08, kaleem ahmad <address@hidden>
wrote:
> From: kaleem ahmad <address@hidden>
> Subject: Re: [Discuss-gnuradio] FSK with RFX2400
> To: address@hidden
> Date: Wednesday, July 23, 2008, 5:23 PM
>
> I have just provided the information which can be helpful for you, and the
> code is also attached with it and a sample received file is also there
> along
> with actual sent file.
>
> Please just scroll up and you will find my message with all this
> information. Additionally OS is 'openSUSI' a favour of Linux. But
if
> you
> still need some more info then please let me know.
>
> Thaks
>
>
>
> Patrick Strasser wrote:
>>
>> kaleem ahmad wrote am 2008-07-23 11:38:
>>> Dear All,
>>>
>>> Can anyone also address the first part of my question aslo, I mean
how
> to
>>>
improve the quality of received data. I mean is it normal with GNU
>>> Radio/USRP that we receive so currupt data or I am doing something
> wrong.
>>> Any suggestion please
>>
>> Before you wrote
>>
>>> after using tune
>>> to set the proper ferquency I was able to run transmitter and
receiver
>> > sussfully. I didnt change anything else in the example.
>> > The problem is data
>>> which I receive is too much corrupt (lot of data errors)..
>>
>> Your description is not very exact. You could help us to help you with
>> more information:
>>
>> What is your setup? OS, distribution, used version of packages, GNU
>> Radio, hardware setup, used parts (cable, antennas), environment.
>> What do you do? Which code do you use?
>> What did you change?
>>
What did you get? Error messages? (add _exact_ transcripts of errors)
>> What did you expect?
>> Please provide exact information, code should be attached. If you
>> changed something, mark the changes so helpers will find it easier.
>>
>> If you have recorded samples of a good and bad transmissions, send us
a
>> representative part of it. If you need to show more than a hand full
of
>> kilobytes, put them on a web server or ftp server and provide a link.
>>
>> Are you sure to have read the FAQ and introducing documentation?
>>
>> Patrick
>> --
>> Engineers motto: cheap, good, fast: choose any two
>> Patrick Strasser <patrick dot strasser at student dot tugraz dot
at>
>> Student of Telematik, Techn. University Graz, Austria
>>
>>
>>
>>
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>>
>>
>
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