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! 
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 A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria
Santa Maria - RS - Brasil
On Mon, Jan 19, 2009 at 09:02:18AM -0200, Ronaldo N. wrote:
usb_rate (signal sample rate) = 2 * f_signal = 8 MHz
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
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 B. [email protected]:
f_signal = 4 MHz
f2=?
These (and your previous questions) are all good.
The USB rate in complex samples/s is 128e6 / interp_rate
Eric
–
Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria
Santa Maria - RS - Brasil
