Tuesday, August 31, 2010

How small can you make antennae?

When we talk about "small antenna", I think about the homebrew antenna I have made for WiFi devices on 2.4GHz.

Now, you can make Yagis for any frequency right? Right, so have a look at this; Antenna directs light at the nanoscale.

"Niek van Hulst and colleagues at the Institute for Photonic Sciences in Barcelona ... fabricated a number of nanoscale Yagi Uda antennas containing the tiny parasitic elements made from gold using lithography to etch the devices onto a glass substrate. The total length of individual antennas was 830 nm where individual feeds were just 145 nm, each separated by 175 nm."

73, Kim

Tuesday, August 10, 2010

Quote of the day by SKR

I've been using this quote in my email for about seven or eight years;
"Art without engineering is dreaming; engineering without art is calculating." Previously I only had th initials; SKR

Today I found out that SKR is none other than Steven K. Roberts. Yes the creator of the Winnebiko and BEHEMOTH!

I started using that quote because it appealed to my inner geek. Especially after I saw a series illustrations from Janet Reid entitled; 'Renaissance Geek'

See the posts on the Make blog; Make it anywhere with a mobile lab;

AHARS Symposium September 19

Event; AHARS Symposium

Topics; Amateur radio, Construction

Speakers; Drew Diamond VK3XU, Phil Harman VK6APH and more

Venue; Belair Community Centre, Corner of Sheoak Road and Burnell Drive, Belair

Cost; $20 at the door for morning tea, lunch and afternoon tea.

Date; 19 September, 2010

Time; 930am - 5pm

Saturday, August 07, 2010

Voltage dividers for 5volt Arduino and 3.3volt SPI devices

I am setting up a radio module to plug into an Arduino.
Specifically the RFM12B like in this schematic;

The Arduino runs at 5volts and the RFM12B runs at 3.3volts. So I have to convert the line levels from 5v -> 3.3v on the inputs to the SPI device and from 3.3v -> 5v for the output.

The example has a 4K ohms and a 10K ohms resistor for the 5v to 3.3v voltage dividers for the Arduino output data lines into the RFM12B, does that sound reasonable?

I did the math and worked through the examples on the Arduino tutorial site and came up with the following values; 1.5K ohms, 2.2K ohms

72, Kim

Thursday, August 05, 2010

usbsoftrock Ubuntu package, from the softrock40 group

Seeing the very lengthy instructions posted recently for how to install a set of SDR software for Ubuntu, I thought I'd make a (very small!) start on reducing that complexity.

This evening I've packaged the first piece of SDR-related software in that set of instructions, usbsoftrock version 1.0.1 , for Ubuntu Karmic, Lucid and Maverick. My initial "very unofficial" packages are (or will very soon be) available in my Ubuntu PPA for download and testing. As part of that process I created a (somewhat minimal) man page for usbsoftrock, so that lintian does not complain about the lack of such a page.

To use my PPA in Karmic, Lucid or Maverick, do:

sudo add-apt-repository ppa:jmarsden/ppa
sudo apt-get update

Then to install this packaged version of usbsoftrock, do:

sudo apt-get install usbsoftrock

and the correct version of the package for your release of Ubuntu (32bit or 64bit, Karmic 9.10, Lucid 10.04, or even Maverick 10.10 if you are running the Alpha version) will be installed for you. If I later update this package, you will automatically be made aware of the update, just as you are for other Ubuntu packages, and you will be able to automatically update it if you wish.

Graphically oriented Ubuntu users who prefer using Synaptic or a similar GUI package manager instead of the shell and apt-get can also add my PPA, and then use their package manager of choice to install usbsoftrock.

Note that this package is untested, because I do not possess any SDR hardware that would allow me to test it! Comments and feedback from those who *do* have such hardware are very welcome. Given sufficient interest, as time allows I will probably package up more SDR-related software for Ubuntu and Debian. Eventually such a set of SDR-related software packages could be added to the official Debian and Ubuntu software repositories, ready for easy installation by end users.

Questions arising:

(Q1) Is usbsoftrock usually used in daemon mode (with the -d option), or in command mode? Since it comes without any init scripts, I am assuming command mode is the usual approach, for now.

(Q2) The COPYING file in the source tarball is GPL-3, but the copyright statements in several of the included source files are "GPL-2 or later". Is there a reason for this? Could it be corrected so the two are consistent? This could help official acceptance into Ubuntu or Debian in future.

(Q3) The two source files interactive.c and interactive.h seem to lack any licence/copyright statement. If these could be added in the same manner as the other files are handled, that could also help official acceptance into Ubuntu or Debian in future.

(Q4) Is there an "official" online place from which the source tarball can be downloaded *without* needing to be a member of this Yahoo Group, and where new releases would appear? This would allow a "watch file" to be created in the package to check for new versions as they are released, etc. There is an automated monitoring system in place for this, but as far as I know it can't work with the files inside a Yahoo group file area, since the monitoring system (obviously) is not a member of all Yahoo groups.

(Q5) Currently my package allows access to the USB device(s) by any user in the 'admin' group. This probably works adequately for Ubuntu, but would probably work rather less well for Debian. Is there any standardization of a "hamradio" or similar group for these kinds of permissions which I should be using?

Lastly, if anyone else is packaging SDR-related software for Ubuntu or Debian, please let me know, so we can collaborate and avoid duplicating our efforts.