Re: [Discuss-gnuradio] Late packet and phase issue

[Marcus D. Leech]

On 10/05/2015 10:58 AM, Leonard Foxes wrote:

Hi list,

It's me again.

I use a USRP N210 with WBX daughterboards and loop back cable to connect TX e RX. I have two problems:

1. Late packet. I use set_time_now and set_start_time command and after few seconds I see some Ls printed.
2. Phase. Phase offset changes between executions. (I'm trying to use set_time_command but nothing changes).

This is my python code about usrp:

self.samp_rate = samp_rate = 500e3

self.USRP_address = USRP_address = "addr=192.168.10.2"

self.tun_freq = tun_freq = 1.45e9

self.tun_gain = tun_gain = 19

self.rx_freq_off = rx_freq_off = 0

self.timeref1= timeref1=time.time()

self.uhd_usrp_TX = uhd.usrp_sink(

        device_addr=USRP_address,

        stream_args=uhd.stream_args(

        cpu_format="fc32", 

        channels=range(1),

        ),

        )

self.uhd_usrp_TX.set_samp_rate(samp_rate)

self.uhd_usrp_TX.set_time_now(uhd.time_spec_t(timeref1), 0)

self.uhd_usrp_TX.set_command_time(uhd.time_spec_t(timeref1+0.1), 0)

        self.uhd_usrp_TX.set_center_freq(uhd.tune_request_t(tun_freq), 0)

self.uhd_usrp_TX.clear_command_time()

        self.uhd_usrp_TX.set_gain(tun_gain, 0)

        self.uhd_usrp_TX.set_start_time(uhd.time_spec_t(timeref1+1))

self.uhd_usrp_RX = uhd.usrp_source(

        device_addr=USRP_address,

        stream_args=uhd.stream_args(

        cpu_format="fc32", 

        channels=range(1),

        ),

        )

        self.uhd_usrp_RX.set_samp_rate(samp_rate)

self.uhd_usrp_RX.set_time_now(uhd.time_spec_t(timeref1), 0)

self.uhd_usrp_RX.set_command_time(uhd.time_spec_t(timeref1+0.1), 0)

        self.uhd_usrp_RX.set_center_freq(uhd.tune_request_t(tun_freq + rx_freq_off), 0)

self.uhd_usrp_RX.clear_command_time()

time.sleep(0.15)

        self.uhd_usrp_RX.set_gain(tun_gain, 0)

        self.uhd_usrp_RX.set_start_time(uhd.time_spec_t(timeref1+1))

Any suggestion will be welcome

Thanks in advance,

Leo

Something to realize is that if you call set_time_now() on two different USRPs, they'll not agree in detail about the time-of-day.  If you're
  using an external 10Mhz and 1PPS reference, you should probably use set_time_unknown_pps(), and make sure that both sides
  of this are setting the same time AT THE SAME TIME.

Also, WBX has a 180deg phase-ambiguity.  Two WBX boards with the same 10MHz reference, on USRPs with the same notion of time,
  will either be in-phase, or 180deg out-of-phase, due to hardware ambiguity in the 2XLO mixer used on WBX.