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Re: [Discuss-gnuradio] Tx path diagram


From: Ronaldo Nunez
Subject: Re: [Discuss-gnuradio] Tx path diagram
Date: Thu, 22 Jan 2009 09:17:15 -0200

Thank you for all Eric. At now I'm editing the diagram (there are some
block which names are in Portuguese).

I understood all when I connected the usrp(basicTX) to the spectrum
analyzer(SA). I verified that when I sweep the frequency (f_LO on
diagram), with f_signal(baseband)=0 Hz, I saw on SA 4 tones, one  at
f_LO , one at 128MHz - f_LO, one at 128MHz + f_LO and other at 200 MHz
(I'm not sure about the last one).

According to usrp_standard.cc the f_LO max is 44 MHz. If you put
tune(target_freq=44e6) without a signal, you will see at least 3
tones:

1st @ 44MHz
2nd @ 128MHz - 44 MHz = 84 MHz
3rd @ 128 MHz + 44 MHz = 172 MHz

If you send a signal, it will be upconverted in those  3 frequencies.
Then, to tx something using a basicTX d'board you will need a RF
filter after it.

Soon I will send the corrected diagram, with the maximum allowable
rates and frequencies.

Regards,

Ronaldo


2009/1/21 Eric Blossom <address@hidden>:
> On Mon, Jan 19, 2009 at 09:02:18AM -0200, Ronaldo Nunez wrote:
>> Hello GnuRadio community,
>>
>> I made a transmission path diagram to try to understand how USRP works.
>> I'm not sure if it's right, if somebody can correct it, it will be great! :D
>>
>> To debug the diagram I used these parameters, but I didn't get the
>> right output (using USRP v1 and BasicTX d'board).
>>
>> ## Defined by user##
>> f_signal = 4 MHz
>> usb_rate (signal sample rate) = 2 * f_signal = 8 MHz
>> L1 = 4
>> f_LO = 5 MHz
>>
>> ## Defined by Software (automatic) ##
>> inter_sample_rate = usb_rate * L1 = 32MS/s
>> f1=?
>> f3=?
>>
>> ## Obtained inside AD9862
>> f2=?
>> f4=?
>>
>> expected f4 = f_LO +/- f_signal = 5 MHz + 4 MHz = 9 MHz
>>                                                    = 5 MHz - 4 MHz = 1 MHz
>> ##Diagram##
>> http://img164.imageshack.us/img164/4476/diageralfinalenusjm4.png
>>
>
> Ronaldo,
>
> These (and your previous questions) are all good.
> Have you tried printing out the result from:
>
>  r = u.tune(...)
>
>  print "r.baseband_freq", r.baseband_freq
>  print "r.dxc_freq", r.dxc_freq
>  print "r.residual_freq", r.residual_freq
>  print "r.inverted", r.inverted
>
>
> The USB rate in complex samples/s is 128e6 / interp_rate
>
> Eric
>



-- 
__________________________________
Ronaldo A. Viera Nunez
Acad├¬mico/Engenharia El├ętrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil




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