The Beagle Has Landed!

The Beagleboard is an open-source hardware project developed around an ARM Cortex A8 processor (TI OMAP3 family). See Beagleboard.org for the general scoop. The Beagleboard-XM shown above sports the DM3730 1 GHz processor with 800 MHz DSP, 512 MB RAM, 4 GB micro SD "disk", 4 USB ports, 10/100 Ethernet, HDMI video, audio in and out. Oh, and an old-fashioned serial port. It is about 3" square and draws 2.5 W on a 5 V power supply.

That's all the hardware you need to run a slew of interesting applications. First, there is Angstrom Linux, which is a distribution tailored for embedded systems. There is also a version of Ubuntu being developed. And you can run other ARM environments, too. Android, anyone? Forth?

I'm interested in some ham applications along the lines of remote control, such as remote receiver systems for HF. The hardware is wonderful, but it's clear that 99% of such a project is software.

Google reveals a number of ham applications already out there:

• OpenSDR work at http://www.opensdr.com/node/10/
• The BeagleBrick at http://www.rarcpio.net/beaglebrick/
• A scanner project at http://djlewis.us/files/projects/beagleScanSpec/

I'd like to hear of others that are active. The net is littered with projects that have been announced in ambitious terms, but aren't heard from again.

Irenic Thoughts

So Hurricane (Tropical Storm) Irene came and went.  This is what it did to my little antenna stack.

2 meters is still pointing north, I think, but the HF SteppIR is off to the northwest, it seems.

Ham Radio Ecclesiastes

"Is there any thing whereof it may be said, See, this is new? it hath been already of old time, which was before us."  Eccl 1:10.

We often hear complaints about the decline of Amateur Radio in one way or another.  Often people say that we just don't build stuff the way we used to.  Well now, 'twas ever thus!

You can read it yourself in the pages of QST for March, 1916.  That's an article by Lloyd Manuel called "Thoughts of the Good Old Palmy Days".  He's talking about his old-time experiences -- probably ca 1905 -- when men were men and hams had to build their own stuff!

This article is a transcription from the QST archives.  You may be interested to browse through selected portions of early QST at history.aa6e.net.

The Sun may be headed for a little quiet time

"Is the solar cycle shutting down?

New results indicate it may very well be, at least temporarily. Even though the Sun is currently approaching the peak of its cycle in 2013, and we’re seeing an increase in activity (more sunspots, flares, and other violent events), there are strong signs that the next expected peak (in 2022 or later) may be weaker, or may not come at all! ..."

(Read more from Phil Plait's Bad Astronomy blog...)

Most Political / Historical QSL Ever?

Up with Bulgaria and savior Russia.  Sorry, Ottoman Turks.

Maybe this isn't the best way to QSL your contact with TA-land?

Bels and Nepers - BSTJ 1929

Today's ARRL Contest Update mentions the on-line availability of all the issues of the Bell System Technical Journal. That's a wonderful thing, because so much of the cutting edge electronic and technical developments of the era 1922-1983 were written up there.  It is a spectacular testament to the value of AT&T's Bell Laboratories.  It is so sad that Bell Labs (and other private research labs like IBM's) no longer have the prominence in fundamental research they once did.

So anyway, enough sentimentality.  I thought I would open up a BSTJ article at random.  Sure enough, it was very interesting.  The first article in the Jan., 1929, issue was Decibel--The Name for the Transmission Unit, by W.H. Martin, wherein the "db" was introduced to the technical public!

Why do we always use "db" instead of bels? AT&T had been using the "transmission unit" for some time, which indicated a ratio of 10**0.1 -- which was identical to the new decibel.  It's a handy unit, too, because it is just about the minimum loudness ratio a person can detect in favorable conditions.

Quick Look at FUNcube Dongle SDR Radio

My candidate for the new radio with the most unlovely name is the FUNcube Dongle.  It is a part of the AMSAT-UK FUNcube satellite project, but it is attracting wide interest (not just for satellite work) as an example of what can be done by a volunteer group to build a very simple, but powerful Software Defined Radio to cover the 60 - 2000 MHz frequency range.  And it's pretty cheap.  The last lot went for £ 108.22 each to the US, about US $170.  They are only being made sporadically, but another batch is supposed to be coming at the end of February.

I have had a chance to borrow an FCD, and I've been trying to figure out what it does and does not do, and whether it's something I need to add to my stable.  Here are some of my lab notes:

My quick tests in my home shack without good signal generation & attenuation showed that the receiver (like any SDR) is sensitive to overload. The only signal source I could use easily was my 2M HT (¼ watt low power) transmitting into a dummy load a foot away from the receiver. I also noted that the dongle radiates at its LO frequency, breaking squelch on the HT. There seems to be little or no shielding on the dongle.  It has a plastic case, and there may or may not be shielding inside.

I used both the basic software combination (FCHid and SpectraVue) and the more user friendly (IMO) WRPlus with the G0MJW adapter DLL. The project's documentation for newbie users is fragmentary and frustrating, but that's understandable at this early stage.

At the ARRL Lab*, I found the FCD's crystal oscillator frequency in this unit is about 119 ppm high, but either software solution allows you to enter a frequency scale factor to correct for this. Warmup drift of nearly 1 ppm was observed from a room temperature start. (Lack of a high stability oscillator or an external sync capability might be a limit in some advanced applications.)

I was able to update the dongle firmware to version 18f, which is current. Surprisingly and unfortunately, I could find no indication in the PC software about what firmware version is actually installed.

I looked at the tweaks available for DC balancing (suppressing the zero frequency peak) and I/Q balance (maximizing image rejection). At 926 MHz, I was able to get 49 dB of image rejection, but the adjustment is critical. Switching to 2000 MHz, the image rejection is down to 30 dB. (Image rejection is typically about 24 dB if you don't do careful tweaking.)

Maximum input level before clipping occurs is about -55 dBm, varying somewhat with frequency.  You can easily reach this level depending on your RF environment.  A preselector filter may be needed.  (Strictly speaking, the -55 dBm limit applies to a simple sinewave input.  It's an instantaneous voltage limit, so a broadband input of greater power might be tolerated.)

A quick measurement of tangential sensitivity gave the following

60 MHz -122 dBm
144    -129
926    -130
1000   -129
2000   -133

Tangential sensitivity is a measure of the the minimum detectable signal. These values are by eye with a particular FFT and filtering setup. Don't hold me to them!

The frequency coverage was at least 60.1 – 2000 MHz.  I did not explore the outer limits of coverage.

The major limitations of the dongle are its limited sensitivity, lack of input filtering or attenuation or AGC, and limited instantaneous bandwidth (96 kHz). The USB dongle package is cheap and effective, but it's susceptible to mechanical damage if it's hanging off your laptop.

For about US $170, it's a steal. It is usable as a wide-coverage VHF/UHF receiver, especially with a low noise preamp, and it provides a good playground for learning about SDR.  I suppose it's even going to be a cheap and effective receiver for satellite work! I would want one as test equipment, but the bandwidth limitation becomes significant if you are searching for a signal with unknown frequency.

Update: The next sale of Dongles will begin Sunday 20 February 2011 22:00UTC.

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*I volunteer in the ARRL Lab in Newington, CT.  The work here is my own and ARRL is not responsible for my mistakes!

Very cool device

http://www.technologyreview.com/blog/arxiv/26194 or
http://arxiv.org/abs/1012.4415

This is a new nanoscale device that can detect RF.  You put in a bias current between D and S, it goes through the graphene (sheet of 1 atom thick carbon).  The graphene sheet resonates mechanically at an RF frequency (33 MHz in the reported device) when a signal is coupled in capacitively from the gate.  The vibration induces a signal on top of the D-S current.  The device works at 77 K (liquid nitrogen temperature), but hopefully can be developed for room temperature operation.