[Discuss-gnuradio] UHD experience

[Per Zetterberg]

Dear List,

I would like to share some UHD experiences in case it can be of any use.

I first modifed rx_timed_samples and tx_timed_samples. The new files are called 
rx and tx and can be obtained from http://www.ee.kth.se/~perz/usrp/uhd/.  An 
assoicated Makefile and matlab files are also there. I installed the UHD 
drivers on two dell E6400 laptops. The two laptops are connected to one USRP2 
each with basic daughterboards. Both daughterboards are fed with the same 
20.1MHz sinusiod which is generated by a Marconi 2024. The 10MHz reference 
output of the Marconi is connected to the REF CLOCK on both USRPs. The PPS 
input is connected to a circuit which can generate a step function which I 
trigger manually.

I then run X=rx(100000,20e6,1,1) from matlab on both PCs. I press return on 
both PCs as synchronously as I can. This starts the rx program (which is a 
modified tx_timed_samples), with 25MHz sample-rate and 20MHz carrier frequency. 
 This function first locks to the REF CLOCK, then it prints " Manually trigger 
the pps!" and does usleep for three seconds. I then activate my step function 
manually. The received signal is then captured and written to harddisc on both 
PCs. I transfer the received signal to the same computer. By plotting X1./X2 I 
can see that the phase offset between the two USRPs is stable. The standard 
deviation of the angular dithering is 0.1degrees. Three consecutive runs give a 
mean offset which varies 0.05degrees.

I redid the experiment with two XCVR2450 daughterboards fed by the same 
Marconi2024 but now at frequency 2400MHz. I tuned the daughterboards to 
2402MHz. The standard deviation of the phase dithering was now 1.8degrees.

I have also tested to transmit locked with REF CLK. I transmitted a sinusoid 
from both USRP2s (basic db). I then watch the sinusoid on an old oscilloscope. 
When the USRP2 are locked to the REF CLOCK the two sinusoids are nicely locked 
while they drift is this not the case.

BR/
Per