Dear Friends, I am Mamoru Yamamoto, a professor in RISH, Kyoto Univ., who is using USRP-1 for dual-band satellite beacon receiver. We use our receivers are used for real research, and are very productive. Thank you. Today I want to ask you a different thing.
We are running another project with USRP-2. This is to develop a radar receiver. We plan to use several (about 7) USRP-2-based receivers for the radar imaging. Thus the receivers must be working with following conditions. (1) Synchronized in frequency and timing with a transmitter. (2) Phase between receivers kept constant. The condition (1) is successful with synchronizing the USRP-2 with outside REF 10MHz or 100MHz, and applying a transmitter pulse to PPS port. Now we face a problem for (2). We can check this by applying the same signal to two USRP-2 receivers. Our symptom is, [a] Phase between output data from two USRP-2 is stable in a single run for hours. (GOOD) [b] But at different runs of the USRP-2, the phase difference are different (= look random). (BAD) Our URSP-2 radar receiver is at 130MHz. Then we use Basic-RX board. One more finding is, [c] If center frequency of the USRP-2 is zero (=0Hz), then the phase difference is stable at different runs. (WHY?) Result of [b] and [c] may show that NCO in the FPGA are oscillating at the same frequency but at different (random) initial phases. At the "zero-frequency" setup, NCO output may be fixed at a certain value like 1+0j, then [c] is realized. I would like to know, -- Is this story true? -- How can we set NCO initial phase equalized at different USRP-2? Wakisaka-kun, one of our students asked a question to this mailing list on October 1st, but not yet get an answer. I attach his E-mail here. The figure is found from, http://www.rish.kyoto-u.ac.jp/~yamamoto/Observation_data.png We are sorry that his writing was not very clear. But we need your suggestions. Thank you very much for your help in advance. Regards, -- Mamoru Yamamoto / RISH, Kyoto University [email protected] Phone +81-774-38-3814, Cell +81-90-5653-7555 === Original question (E-mail from Mr. Wakisaka) === Subject: About synchronize two USRP2s using external reference (SMA) I tried to synchronize two USRP2s using external reference (SMA). I input 10-MHz signal to REFCLOCK pin and a trigger in PPS IN. I modified rx_streaming_samples.cc and wrote the following code u2->config_mimo(usrp2::MC_WE_LOCK_TO_SMA); I use txrx_raw_eth_20100608.bin and u2_rev3-20100603.bin. but I failed to synchronize two USRP2s. I synchronized start timing using PPS but two USRP2's signal have phase difference. This phase difference change every observation. Some figures are attached. -- Figure -- http://www.rish.kyoto-u.ac.jp/~yamamoto/Observation_data.png In this case, I input RF signals of 130 MHz + 0.05 MHz to RF1 and set as follows: Center frequency: 130 MHz Decimation: 4 When I don't set center frequency, two USRP2's signal don't have phase difference. So I suppose this is due to the phase difference between NCOs of two USRP2. What should I do? Many Thanks. Youhei Wakisaka. ========================= _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
