April 2009

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srrctl, a Perl script to control a Quintech L-band switch

2009-04-28 15:51 +00:00 | No comments

We use Quintech SRR2150 L-band switches at our teleports. These are simple devices for switching L-band inputs and outputs. The most common application for one is to switch inputs to a spectrum analyser. This allows me to use one spectrum analyser to monitor several inputs (multiple antennas, multiple polarisations on the same antenna, etc).

Quintech’s switches are pretty basic. They have a front control panel, an interactive shell accessible by serial or telnet, and a custom communications protocol over 9100/TCP. Quintech provide a basic Windows management application, but it is either rudimentary (version 1.0) or totally broken (version 2.06). Why not control it from the command line? Thankfully Quintech have fully documented their management protocol, and implementing it in Perl was a few hours’ work back in 2007.

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My HTPC setup

2009-04-15 21:19 +00:00 | 7 comments

As I mentioned in my last post, I now have a Home Theater PC (HTPC). Want to look under the hood?

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Enabling 1080p video on the Shuttle X27D HTPC

2009-04-14 21:10 +00:00 | 9 comments

I recently bought a Shuttle X27D to use as a Home Theater PC (HTPC). The reviews of this hardware run from disappointing to average, but I’m reasonably happy with it. It’s quiet (just one small fan for the GPU, and none for CPU, case, or power supply), uses little power (I measured it at 32 W in full operation), and the analog audio jack on the motherboard has no discernable noise in the audio stream (unlike my Dell Vostro 1500 laptop).

Unfortunately, the Intel 945G graphics processor can’t reliably handle 720p @24 frames video. I tested with a downloaded copy of Sita Sings the Blues, and it dropped frames as the animated fireworks exploded during the title sequence. It was fine with most of the rest of the film. Still, it means I’m likely to stick to upscaled 480p video. Which is far better for my bandwidth usage.

Naturally, I ran into some problems setting it up.

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Adding a local respository to pbuilder

2009-04-09 13:46 +00:00 | 2 comments

I recently posted about backporting packages with pbuilder. Someone asked about forward porting PHP4, which is a huge task. PHP4 is out of date, and the entire set of PHP4 libraries has a lot of build dependencies, including some packages you must build yourself. I’m not going to take you through the process of backporting PHP4. If you really need it, you can install php4-cgi and php4-* from Ubuntu dapper directly on hardy. But I will show you how to enable a local repository in pbuilder. This will allow you to build a package with pbuilder, and then use that package to satisfy any build-dependencies that other packages need.

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Sun Java Firefox plugin working on Ubuntu Hardy amd64

2009-04-08 18:45 +00:00 | 7 comments

Finally, finally, FINALLY! The Sun Java plugin now works on Firefox amd64 in native 64-bit. It has already been included in Ubuntu 9.04 Jaunty, but the packages work just fine on Hardy as well, and probably on Intrepid.

Just download and install the Jaunty versions of sun-java6-bin, sun-java6-jre, sun-java6-fonts, and sun-java6-plugin. Install them, and remove the old icedtea plugin if you have it:

sudo dpkg -i sun-java6-bin_6-13-1_amd64.deb sun-java6-fonts_6-13-1_all.deb sun-java6-jre_6-13-1_all.deb sun-java6-plugin_6-13-1_amd64.deb
sudo apt-get remove --purge icedtea-gcjwebplugin

Then restart Firefox and Sun java will load natively 64-bit. Check it:

tyler@baal:~$ java -version

java version "1.6.0_13"
Java(TM) SE Runtime Environment (build 1.6.0_13-b03)
Java HotSpot(TM) 64-Bit Server VM (build 11.3-b02, mixed mode)

I’ve included them in the repository.

Update 2009-07-16: A more recent version is now available in the hardy-updates repository. I have removed the above copy from my repo. Intrepid users should upgrade to jaunty anyway, but can still download packages directly.

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Carrier sizing and the decibel scale

2009-04-07 17:11 +00:00 | No comments

In the satellite world we frequently work with the decibel scale. Decibels (dB) are a way of expressing the relative difference in signal strength between two sources. It is a logarithmic scale, so increasing numbers represent an exponentional increase in power. In simple terms, they are a convenient way of using addition instead of multiplication.

There are plenty of good places to understand decibels. I want to focus on how this helps us answer a few important questions in carrier sizing.

  1. I have two carriers, P1 and P2. What is the difference in power (Y) between them? Commonly this question appears as “Customer has capacity P1 and wants P2. How much additional power does he need to support the new carrier?”
  2. I have carrier P1 of a certain size, and Y dB margin (additional power available). How large can I make my new carrier P2? Or if Y is negative, how small?

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