28 July 2014

587. Very Briefly: Getting pictures off of a corrupted Compact Flash card using testdisk

Nothing terribly complicated here. My CFII card (above, at /dev/sdb1)  is about a decade old and occasionally becomes corrupted. To recover the photos I use photorec which is part of testdisk:

sudo apt-get install testdisk
sudo photorec

Select the correct device, in this case /dev/sdb


Pick the correct file system, typically FAT16 or 32
Also select a place to store the recovered photos. Then recover:

And you're done.

586.Very Briefly: Gnuradio, RTL-SDR, GQRX and an R280T device on debian jessie

* I did this on debian jessie which at the time has gnuradio v 3.7.3-9+b1 and rtl-sdr v 0.5.3-3

* I'm having a lot of trouble getting gqrx working on debian wheezy even with backports. Whereas the backports versions of gnuradio, rtl-sdr and gqrx-sdr install just fine, when running gqrx I get the following error:
gqrx: symbol lookup error: /usr/lib/x86_64-linux-gnu/libQtNetwork.so.4: undefined symbol: _ZN16QIODevicePrivate13putCharHelperEc
* gqrx won't work on debian wheezy systems with 2 Gb of memory for some reason. I get the same error as is shown in this post: https://groups.google.com/forum/#!topic/gqrx/20F8RMWkNbU

The post:
I recently bought a DVB USB dongle based on RTL2832 and R280T: http://www.ebay.com.au/itm/221450623699?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649. AU$11for a TV card which actually works flawlessly under linux really isn't bad!

As I already have a mythtv setup using leadtek DTV 1000S I was more interested in exploring the R820T dongle as a software defined radio (SDR).

 So, after glancing at  http://www.thepowerbase.com/2012/06/getting-started-with-rtl-sdr/2/ I did the following

sudo apt-get install rtl-sdr gnuradio gnuradio-dev libgnuradio-osmosdr0.1.1.4 git libboost-dev liblog4cpp5-dev libboost-system-dev libboost-program-options-dev checkinstall
mkdir ~/tmp
cd ~/tmp
git clone https://github.com/csete/gqrx.git gqrx.git
cd gqrx.git/
mkdir build
cd build
qmake ../
sudo checkinstall --install=no
0 - Maintainer: [ root@niobium ] 1 - Summary: [ gqrx ] 2 - Name: [ gqrx ] 3 - Version: [ 20140726 ] 4 - Release: [ 1 ] 5 - License: [ GPL ] 6 - Group: [ checkinstall ] 7 - Architecture: [ amd64 ] 8 - Source location: [ build ] 9 - Alternate source location: [ ] 10 - Requires: [ ] 11 - Provides: [ build ] 12 - Conflicts: [ ] 13 - Replaces: [ ]
sudo dpkg -i gqrx_20140726-1_amd64.deb

Starting gqrx and using it is easy:
So far I haven't managed to get anything other than regular commercial radio signals (I've only explored the FM band).

17 July 2014

585. Very briefly: use latex to combine .eps files into a single .eps

Say you have a figure made up by several smaller images by combining several includegraphics statements. Say also that you need to submit the figure as a single file when uploading the final version of your article.

The first step is to make sure that the output .ps file fits flush to the figure (see http://texblog.org/tag/fit-page-to-content/) using the standalone class:
\documentclass[varwidth=true, border=10pt, convert={size=640x}]{standalone} \usepackage[english]{babel} \usepackage{graphicx} \begin{document} \begin{figure}[h] \begin{center} \includegraphics[width=2.0cm]{figure_1a.eps} \includegraphics[width=2.0cm]{figure_1b.eps} \includegraphics[width=2.0cm]{figure_1c.eps} \\ \includegraphics[width=2.0cm]{figure_1d.eps} \includegraphics[width=2.0cm]{figure_1e.eps} \end{center} \end{figure} \end{document}
Then use ps2eps to turn the ps into an eps file:

ps2eps combined_image.ps