# Tx path diagram

#1

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=?

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

Santa Maria - RS - Brasil

#2

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

#3

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

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