Using gr.head with multi-channel receiving

Hello,

I am trying to receive two channels at once with the USRP N210 and a
TVRX2
daughterboard. My code to set up the top block is below:

class collect_double_tb(grc_wxgui.top_block_gui):

def
init(self,centerfreq0,filename0,centerfreq1,filename1,nsamples):
grc_wxgui.top_block_gui.init(self, title=“Top Block”)
_icon_path = “/usr/share/icons/hicolor/32x32/apps/gnuradio-grc.png”
self.SetIcon(wx.Icon(_icon_path, wx.BITMAP_TYPE_ANY))

##################################################
# Variables
##################################################
self.samp_rate = samp_rate = 20000000

##################################################
# Blocks
##################################################

self.uhd_usrp_source_0 = uhd.usrp_source(
  device_addr="",
  stream_args=uhd.stream_args(
    cpu_format="fc32",
    channels=range(2),
  ),
)

self.uhd_usrp_source_0.set_subdev_spec("A:RX1 A:RX2", 0)
self.uhd_usrp_source_0.set_samp_rate(samp_rate)
self.uhd_usrp_source_0.set_center_freq(centerfreq0, 0)
self.uhd_usrp_source_0.set_gain(3, 0)
self.uhd_usrp_source_0.set_center_freq(centerfreq1, 1)
self.uhd_usrp_source_0.set_gain(3, 1)
self.gr_file_sink_0 = gr.file_sink(gr.sizeof_gr_complex*1, 

filename0)
self.gr_file_sink_0.set_unbuffered(False)
self.gr_file_sink_1 = gr.file_sink(gr.sizeof_gr_complex*1,
filename1)
self.gr_file_sink_1.set_unbuffered(False)

self._head0 = gr.head(gr.sizeof_gr_complex,int(nsamples))
self._head1 = gr.head(gr.sizeof_gr_complex,int(nsamples))

##################################################
# Connections
##################################################
self.connect((self.uhd_usrp_source_0, 0),self._head0,

(self.gr_file_sink_0, 0))
self.connect((self.uhd_usrp_source_0, 1),self._head1,
(self.gr_file_sink_1, 0))

Then, to run this top block, I run:

tb = collect_double_tb(f0,filename0,f1,filename1,nsamples)
tb.run()
tb = None

The problem is, no matter what I set nsamples to, I always get a 17.4 kB
file. Are there limitations with using gr.head this way with two
channel
reception? Or, is there a better way to g about collecting a specific
amount of data with two channels receiving simultaneously?

Thank you,

SW


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