Not recording it all

GNU Radio
1

I ran my “record” setup for over 10 seconds, but when I run the data
file
back through my “playback” I only get about two seconds (if that) of
result. What happened to all the data, and how can I change things next
time to get all the data?

My record setup is as follows:

Rate: 50M
USRP Source
Low Pass Filter
Decimation: 50
Cutoff Freq: 15M
Transition Width: 5M
File Sink

Paul B. Huter

2

On Sat, Nov 23, 2013 at 10:44 AM, Paul B. Huter [email protected]
wrote:

 Decimation: 50
 Cutoff Freq: 15M
 Transition Width: 5M

File Sink

Paul B. Huter

Try this. You only want to capture for a certain length of time, which
means a certain number of samples. So put a gr::blocks::head block
between the filter and file sink. The number of items you’ll want is
going to be samp_rate (samps/sec) * time (secs) (and we know samp_rate
here is 1 Msps). That will store exactly that many samples and then
shut down the application.

Tom

3

Thanks, Tom. Just to clarify, the 1Msps comes from the sample rate of
50M
and the decimation of 50, correct? Also, is this going to record 10
seconds
of “real-time” data? I was having issues with real-time, due to the
large
data stream, so will this record data from t=0 to t=10, just not in
real-time?

Paul B. Huter

4

On Sat, Nov 23, 2013 at 11:02 AM, Paul B. Huter [email protected]
wrote:

Thanks, Tom. Just to clarify, the 1Msps comes from the sample rate of 50M
and the decimation of 50, correct? Also, is this going to record 10 seconds
of “real-time” data? I was having issues with real-time, due to the large
data stream, so will this record data from t=0 to t=10, just not in
real-time?

Paul B. Huter

If you’re not running in real time, then you’re dropping samples. The
way these devices work is that they drop packets of samples, which can
be quite a lot of data. So you’ll store in your file sink 10 seconds
worth of data, but if you’re dropping samples, it won’t be 10
consecutive seconds of data.

But I just realized something. We’ve been trying to help you out
constructing your filters and everything, but why are you setting your
input sample rate to 50 MHz only to down-convert in software? The USRP
will do that for you! You can ask the USRP to set the channel and
sampling rate to what you want, then you just take that input and
capture it. It’s done it all for you! And since you’re talking about
just taking samples for a small amount of time, it’s not like you’re
trying to use this concept to quickly change channels instantaneously.
So why not let the hardware do the work for you?

Tom

5

Can I do that through GNU Radio, or is that a configuration I need to
make
through the USRP (ie Do I need to run the setup for the USRP)?

Paul B. Huter