RE: Why I cannot see a TX pulse and the RX pulse in the same oscilloscope in time domain

Hi,

I think I did not provide enough details.

I am using basic TX and basic RX. My idea was to measure delay between
the
tx pulse and the rx pulse but I cannot because the rx signal is not
stable
in the oscilloscope. The delay between the signals is random. It can be
0.075 ms, 0.30 ms (see images) sometimes the pulse is even
negative!..it
doesn’t make sense to me.

My GRC file is:

<?xml version='1.0' encoding='ASCII'?>

<flow_graph>
Wed Oct 13 10:03:03 2010

options

id
top_block


_enabled
True


title



author



description



window_size
1280, 1024


generate_options
wx_gui


category
Custom


run
True


realtime_scheduling



_coordinate
(10, 10)


_rotation
0



usrp2_sink_xxxx

id
usrp2_sink_xxxx_0


_enabled
True


type
complex


interface



mac_addr



interpolation
500


frequency
90000000


lo_offset
float(‘inf’)


gain
0


_coordinate
(1034, 26)


_rotation
0



usrp2_source_xxxx

id
USRP2_source


_enabled
True


type
complex


interface



mac_addr



decimation
500


frequency
90000000


lo_offset
float(‘inf’)


gain
0


_coordinate
(209, 208)


_rotation
0



gr_null_sink

id
gr_null_sink_0


_enabled
True


type
float


vlen
1


_coordinate
(957, 308)


_rotation
0



gr_float_to_complex

id
gr_float_to_complex_0


_enabled
True


vlen
1


_coordinate
(669, 59)


_rotation
0



gr_complex_to_float

id
gr_complex_to_float_0


_enabled
True


vlen
1


_coordinate
(636, 272)


_rotation
0



wxgui_scopesink2

id
wxgui_scopesink2_0_0_0_0


_enabled
True


type
float


title
Scope Plot


samp_rate
200000


v_scale
0


t_scale
0


ac_couple
False


xy_mode
False


num_inputs
2


grid_pos
1,1,1,1


notebook



_coordinate
(863, 151)


_rotation
0



gr_vector_source_x

id
gr_vector_source_x_0


_enabled
True


type
float


vector
1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0,
0, 0, 0


repeat
True


vlen
1


_coordinate
(205, 124)


_rotation
0



gr_throttle

id
gr_throttle_0


_enabled
True


type
float


samples_per_second
200000


vlen
1


_coordinate
(428, 165)


_rotation
0



<source_block_id>USRP2_source</source_block_id>
<sink_block_id>gr_complex_to_float_0</sink_block_id>
<source_key>0</source_key>
<sink_key>0</sink_key>


<source_block_id>gr_float_to_complex_0</source_block_id>
<sink_block_id>usrp2_sink_xxxx_0</sink_block_id>
<source_key>0</source_key>
<sink_key>0</sink_key>


<source_block_id>gr_complex_to_float_0</source_block_id>
<sink_block_id>gr_null_sink_0</sink_block_id>
<source_key>0</source_key>
<sink_key>0</sink_key>


<source_block_id>gr_throttle_0</source_block_id>
<sink_block_id>gr_float_to_complex_0</sink_block_id>
<source_key>0</source_key>
<sink_key>0</sink_key>


<source_block_id>gr_throttle_0</source_block_id>
<sink_block_id>wxgui_scopesink2_0_0_0_0</sink_block_id>
<source_key>0</source_key>
<sink_key>0</sink_key>


<source_block_id>gr_complex_to_float_0</source_block_id>
<sink_block_id>wxgui_scopesink2_0_0_0_0</sink_block_id>
<source_key>1</source_key>
<sink_key>1</sink_key>


<source_block_id>gr_vector_source_x_0</source_block_id>
<sink_block_id>gr_throttle_0</sink_block_id>
<source_key>0</source_key>
<sink_key>0</sink_key>

</flow_graph>

If it is important, I get a lot of messages like:
usrp2::tx_raw: FIXME: short packet: 7 items (56 bytes)
usrp2::tx_raw: FIXME: short packet: 7 items (56 bytes)
usrp2::tx_raw: FIXME: short packet: 7 items (56 bytes)

Many thanks,
Jorge

Hello all,

I did some test when transmitting and receiving a pulse. After seeing the
transmitted and received signal on a single oscilloscope (in GRC).

Flowgraph:
Vector source - Oscilloscope A - Rational resampler - USRP2 sink (500
interpolation)
USRP2 source (500 decimation) - Rational resampler - Oscilloscope A - Nule
sink

The received pulse signal is not stable (oscilloscope triggered with tx
signal). It is like random phase so that I can not measure the delay
between
transmitted and received pulse.
I expected to have two fix pulsed signals in the oscilloscope at a fixed
delay.How can I do it?

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