It seems Logitech is going entirely to 2.4 GHz for their mice. This is very disappointing, as the spectrum is so crowded. I’d love to switch, but the interference problems with wifi are horrible. The tiny “unifying receiver” used by their new devices is pretty slick too, but I doubt you could put an effective 27 MHz antenna in such a small dongle. Does anyone make a modern mouse which doesn’t use 2.4 GHz or bluetooth?

I read an article in the Dec 2009 issue of Linux Magazine, one of several Linux-focused magazines we get at the office. I’d like to link directly to it, but it the magazine’s own website doesn’t offer the article or even a reliable permanent link to the issue number. Hint: hey guys, sort that out.

The article was about configuring ACPI hotkeys to support your specific laptop. IE, the buttons for “sleep”, “brightness up”, etc. For most laptops this already works on Ubuntu. On my Dell Vostro 1500, every button except for “sleep” worked right after install. This is Linux, so there is always some way to fix that.

Unfortunately, ACPI cannot even detect my keypress. The instructions in the article suggest starting acpid with -d for debug mode, which will print any keypresses that reach it. Pressing Fn+F1, the sleep button, prints nothing. So we’re going to use KDE’s hotkey support instead. Gnome users can use a similar method; only the menu instructions differ.

First, create a script somewhere your user can run. I have $HOME/bin in my $PATH, so I created a file there:

touch ~/bin/sleep-kde-screen
chmod 755 ~/bin/sleep-kde-screen

Then I edited it to contain the following:

#!/bin/sh
qdbus org.freedesktop.ScreenSaver /ScreenSaver Lock
sudo /usr/sbin/pm-suspend

This calls DBUS to lock the screensaver, then asks power-manager to suspend. This way you will be prompted for your password when you resume from suspend. If you prefer to hibernate, change “pm-suspend” to “pm-hibernate”.

Second, you need to tell sudo to allow your user to run this /usr/bin/pm-suspend without prompting for a password. Run sudo visudo to edit /etc/sudoers, and add this line at the bottom:

%admin ALL=NOPASSWD: /usr/sbin/pm-suspend

Finally, add this script to your K menu with a hotkey. Right-click on the K menu and select “Menu Editor”. Add a new item to the “System” menu, give it a name (I like “Sleep!” *), and tell it to call sleep-kde-screen (wherever you’ve put it). On the Advanced tab, select “Current shortcut key” and press the sleep button. Now save and close the menu editor.

* I imagine saying “Sleeeeeep!” like a hypnotist bad guy from an old movie on MST3K.

Press the sleep button, and you’ll suspend!

The 2.4 GHz spectrum is extremely crowded, especially in cities. It is commonly used for 802.11b/g wifi, baby monitors, wireless video cameras, and wireless television “extenders”. Plus, devices like microwaves make a huge amount of noise in this spectrum. In fact, microwaves use 2.4GHz to heat food because it is readily absorbed by water. So don’t put your access point in your kitchen.

I first noticed a problem with my mouse a few months ago. Sometimes the mouse movement became stuttery and a click wouldn’t register. The problem coincided with the time that Bacula runs its daily backup of my laptop. So I initially believed it to be some kind of bus issue with my laptop’s motherboard.

Then one day I was testing a wifi issue with my WiSpy 2.4 GHz spectrum analyser. I know that 802.11 has a lot of issues with spectrum overlap between channels, which effectively means that only channels 1, 6, and 11 are useful for wifi. But since I’ve also been working in satellite, I know that transmitters have intermodulation effects outside the expected spectrum. This can lead to noise in adjacent channels. So I decided to see if this happened to 802.11 signals.

My office network uses 802.11 channel 11, which is 2.462 GHz. Here is the spectrum when the network is idle. The full width of a network on channel 11 is overlayed with a blue column.

idle network on channel 11

Now here is the same network, while I’m running a “ping -f” to my office router.

intermodulation effects of busy network on channel 11

As you can see, even through my network is on channel 11, my wireless card generates 30 dB of noise on channel 6 and 20 dB of noise on channel 1. My V450 currently operates on channel 3, and it generates only 10 dB of carrier above the noise floor. When that carrier gets swamped by 20 dB of noise, such as when I’m uploading a file, the mouse stutters.

So I switched to a 27 MHz mouse. And now my wireless mouse is just as reliable as a wired one, and far more convenient. Recommendations on other, good-quality mice that don’t use 2.4GHz are appreciated.