[Discuss-gnuradio] How to use the TV board?

[Nick Stephens]

Hello Everyone - I am doing my best to understand how the TVRx board
works. I have Rev. 3 of the TV board, with MicroTuner module with IF of
~44 MHz.

(Preface - Thanks for your patience, as I am relatively new to GNU radio
and the USRP!)

In my experiment, I have an 80 MHz sine wave at 2 mV pk-pk input to the
TV tuner from a function generator. The goal is to properly record this
signal to a data file, then plot the time domain and FFT of the signal
in Matlab to verify functionality.

My record script is from the examples directory:

#!/usr/bin/env python

"""
Read a specified number of samples from a USRP and write the data to
a file.
"""

from gnuradio import gr, eng_notation
from gnuradio import usrp
import sys

class record_graph(gr.flow_graph):
    def __init__(self):
        gr.flow_graph.__init__(self)

        self.u = usrp.source_c(which=0, decim_rate=8)
        self.dst = gr.file_sink(gr.sizeof_gr_complex, 'recorded.dat')
        self.head = gr.head(gr.sizeof_gr_complex, 5000)

        self.connect(self.u, self.head, self.dst)

        self.u.set_mux(usrp.determine_rx_mux_value(self.u, [1,0]))
        self.subdev = usrp.selected_subdev(self.u, [1,0])
        self.subdev.set_gain(10)
        tuning = self.u.tune(0, self.subdev, 79000000)
        print "baseband_freq:", tuning.baseband_freq
        print "dxc_freq:", tuning.dxc_freq
        print "residual_freq:", tuning.residual_freq
        print "inverted:", tuning.inverted
        fs = self.u.converter_rate()
        print "source converter rate:", fs

try:
        record_graph().run()
except KeyboardInterrupt:
        pass

----
Now, as I understand it, with my tuning target frequency in this code at
79 MHz and a decimation rate of 16, and 64 MS/s sampling, then the sine
wave signal should appear at approximately a 1 MHz frequency. However,
all I am seeing is wideband noise. Does anybody know why this may be?
Also, what can you tell me about using the TV board?
-- 
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