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Re: [Discuss-gnuradio] *much* faster filtering --- plus vhf mountaintopp

From: James Cooley
Subject: Re: [Discuss-gnuradio] *much* faster filtering --- plus vhf mountaintopping
Date: Wed, 11 May 2005 10:19:25 -0400
User-agent: Mozilla Thunderbird 1.0.2 (X11/20050317)

I have successfully used an external USB 2 drive along with the usrp, no problems. And that's with a USB hub with USB2 drive as well as a GPS attached and spewing data. There's a trick, though.... compression. You can make a fifo, ask gnuradio to write to it, and zip it.

In one window, make the fifo and start it:

#> mkfifo testfifo
#> cat testfifo | gzip -c > data.gz

In another, start up the capture, something like this:

#> usrp_rx_file.py -o testfifo

THE reverse step is to unzip,, like this (for example, with the wfm script):

#> wfm_rcv_file.py testfifo

In the other window, do:
#> gzip -dcf data.gz > testfifo

Seems to work barely on my laptop, which is a 1.6 GHz pentium M machine.... HOWEVER, to aid things along even more, I did the captures without using X-windows (you don't need it if your not using any guis). You can switch consoles in linux with ctl-alt-Fx, where F7 is where your x-windows is running. I switched to a console, killed X, used one console for the usrp, the other for the piping and zipping.

How well did it work? I did a sweep of the entire front-end's range, about 40 minutes of sampling incrementing by 400kHz about every second from 50 Mhz to 860 MHz... this gave me a zipped file roughly 600MB.

For usrp source, complex samples, decim 8 (therefore, rate= 8Mbits/sec), this worked out well. By the way, Chuck, I think that if you're using a TVRX board, the downconverter 4937 has a 6 MHz bandwidth... so even though you captured at 8Mhz, don't you only have just 6 of useable data?


Daniel O'Connor wrote:

On Wed, 11 May 2005 21:43, Chuck Swiger wrote:
for about 3 or 4 minutes each before filling up 20Gb free space. Still it's
nice to collect
field data for later slicing and dicing in the basement.

Looking for faster/bigger portable storage. The Adaptec SlimSCSI 1480 card
will only do

If you can power a mains appliance (car inverter?) you could use an external firewire drive.

I doubt you could run a USB enclosure and the USRP without running out of USB bandwidth but firewire should be OK.

The enclosures I've used (Mapower) can keep up with WDxxxxJB drives which do around 30-50Mbyte/sec.


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