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Re: [Discuss-gnuradio] Problem with capture playout WBX daughterboard US

From: Bastien Auneau
Subject: Re: [Discuss-gnuradio] Problem with capture playout WBX daughterboard USRP N210
Date: Tue, 23 Aug 2011 18:28:31 +0000
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:6.0) Gecko/20110812 Thunderbird/6.0

Hi Josh

I'll stop flying blind for now
But I'm not sure what else can be done ?!

We are using USRP to create a DVB-RCS terminal
We already have a commercial product using another HW platform
We are now moving this product to the USRP N210 platform
UHD programming has been mostly done, especially regarding time settings
(as DVB-RCS is TDMA).
To make it short, we now have a proto-terminal that can transmit data at
required time using timestamp. Next step is to send some hard coded
data, to ensure that the system is fine (especially the time stability,
using DVB-RCS burst receiver as time reference). Following step is to
actually create the burst to send (coding and modulation done in mathlab).

So we want now to send some hard coded data (a specific burst). In order
to test the system and avoid problem on the burst generation side. The
idea is to capture for a couple of second, a signal that contain wanted
burst. Then use these captured burst to transmit theme at regular interval.

To do that, we are using the example script to capture the data (and the
tx example to test that captured data is correct)
There is no processing of the file, except for what the provided
examples do.

We tried first to capture a signal from a DVB-RCS commercial terminal
that we own, but this did not work. Then tried the same with a live
signal from the air.

When did it go wrong ?
Why playing out data just captured (using strictly same parameters) is
"flying blind" ?
Do you have any suggestion on how to acquire a burst for later use
(except generating it, as we want to avoid that for now)?

Best Regards

On 08/23/2011 10:36 AM, Bastien Auneau wrote:
> Hi All
> Using USRP N 210, WBX board, GPSDO, UHD 3.2.2, under Windows 7
> We want to use the example scripts to capture then playout a signal we
> get from the air (satellite link with bursts). We proceed as follow :
> 1. capture using rx_samples_to_file.exe --type short --rate 10000000
> --freq 1057232000 --gain 10
> 2. playout the newly captured file
> tx_samples_from_file.exe --type short --rate 10000000 --freq 1057232000
> --gain 2
> 3. Using a spectrum analyzer, we expect to see similar things when
> looking at signal from air (few small carriers, bursty), than when
> looking at USRP played out signal.
> But the USRP only output an around 2.5 MHz carrier, which does not
> contains the burst of the original carrier (looking on live signal the
> centered carrier constantly goes up and down). The carrier is extremely
> steady during all the playout time. Also, the doc
> (http://www.ettus.com/downloads/ettus_daughterboards.pdf) specifies
> 30MHz bandwidth, why can't we see the same bandwidth from played out
> signal than from original signal ?
> Also, we use the rx/tx port of the WBX board to capture then to playout
Here is my take on your method:


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