brainwagon

G3XBM posted a link to VE7SL’s nifty LOWFER beacon transmitter, setup to run around 188khz. I’m still fascinated by LF operation under Part 15, and this circuit is just about as simple as you can get. Very neat. Preserved for later consumption.

It’s too late, I should be in bed, but once again I’m reading up on low frequency radio communication, another of those oddball interests you pick up when you read too much. I blame tuning around with the SDR-IQ this evening, where I found that a number of DGPS beacons were easily heard down around 314Khz. Trying to find more information lead me to W3EEE’s excellent LF website, which makes me think that perhaps I should try receiving NAVTEX beacons sometime. Good stuff.

W3EEE – Mt. Gretna, PA, U.S.A.

I’ve been interested in all kinds of machine tools for a long time, and in the various projects like Rep Rap and the like that use either additive or subtractive technologies. Now that I am involved more in radio stuff, the prospect of milling small pc boards seams very cool, and this little CNC mill seems to fit the bill. Preserved for later.

Jonathan Ward – MIT – Machines That Make.

Diane, VA3DB passed along this excellent page detailing the inner workings of the Gilbert Cell mixer. I was interested in these primarily because I was trying to understand the inner workings of the NE602/SA602/SA612, and was looking at an LTSpice model of it, and couldn’t understand the way that the various transistors were biased. I haven’t had time to read over this page too closely, but amidst the math I suspect the answer can be found.

Gilbert Cells.

Earlier tonight, I noticed that CW traffic on 40m picked way up. You get an interesting view of the band conditions when you can tune 100Khz at a time:

Even with my own wimpy antenna, it was hopping pretty good.

Digital Radio Mondiale is a new digital broadcasting standard that is being used on shortwave. Sadly, its one of those annoying standards that relies on all sorts of patented technology, which makes experimentation really difficult and annoying. But I heard that Sackville Canada echoed Radio Chinas DRM broadcasts here to the U.S. for an hour a day, so I set up my new SDR-IQ to record ten minutes of it while I was at work the other day. Here’s the spectrogram, showing the near solid block of DRM right in the middle:

It took me a few tries to figure out how to decode this. In the end, what I did was playback the I/Q recording with Spectravue. The signal was centered around 6.080Mhz, so I tuned the SDR-IQ ten kiloherz below, and put it into WUSB mode, after adjusting the filters to pass between 3Khz and 18khz (I left some slop on both sides). I then re-recorded the demodulator output into a wav file. While you can’t open wav files directly from the menus, if you invoke the drm decoder with the wav file as an argument, it will use the wav file as input. I then recorded the resulting decode using Audacity. Here’s a sample. There are some drop outs, but overall the quality is quite good. It would be a bit better if I didn’t recompress the output as an MP3, but hey, it’s a faster download this way.

Digital Radio Mondiale of Radio China, via Sackville, CA

I’m not sure what this is good for, but it was an interesting experiment for my new radio.

Phillip Torrone pointed out a dreadful article on CNN.com today:

Digital piracy hits the e-book industry – CNN.com

A few things that I’d like to directly comment on:

“With the open-source culture on the Internet, the idea of ownership — of artistic ownership — goes away,” Alexie added. “It terrifies me.”

This is dreadfully annoying, because “open-source culture” has nothing whatsoever to do with piracy. Open-source culture is actually based upon the idea that artists should be allowed to choose (for themselves! gasp!) the conditions under which their works are used and shared. Nothing in the open source world does anything to deprive anyone of anything they own: indeed, to be enforceable, it absolutely relies on copyright law. But even more annoying is that someone can be quoted in a CNN story basically equating open source culture with piracy.

“Textbooks are frequently pirated, but so are many other categories,” said Ed McCoyd, director of digital policy at AAP. “We see piracy of professional content, such as medical books and technical guides; we see a lot of general fiction and non-fiction. So it really runs the gamut.”

Textbooks are an interesting case: they are frequently pirated for a couple of reasons. First, they are enormously expensive. Ridiculously expensive. 25 years ago when I was in college, they were expensive, but now, they are ridiculously so. What’s more is that publishers have worked hard to destroy any potential resale value for books on the used market. They do this by deliberately obsoleting books by creating only short runs of a version of a textbook, immediately replacing it with a “new version”. In order to keep all students using the same version of the text (for uniformity), professors are then required to ask that all students use the most recent and available version of the text. This drives down resale prices for the old versions, and creates a single supplier situation for the publisher. Combine this with attempts to “license” medical and legal textbooks to students, and it’s no wonder that students seek a way to reduce the $500-$1000 or more that they’ll spend on books in a semester.

Some publishers may try to minimize theft by delaying releases of e-books for several weeks after physical copies go on sale. Simon & Schuster recently did just that with Stephen King’s novel, “Under the Dome,” although the publisher says the decision was made to prevent cheaper e-versions from cannibalizing hardcover sales.

Guess what? That’s not going to work. Here’s why. Projects like DIYBookScanner already exist, and can be replicated for a few hundred bucks. Using a book scanner, any hardcover book can be converted into digital form in a matter of hours. And as (I think) Mike Godwin said, digital piracy isn’t like trying to keep cows in a corral. All it takes is one smart cow to break the copy protection or scan a book, and then thousands of other cows can follow suit. And quite frankly, there is no possible way to stop it.

Some authors have even gone as far as to shrug off e-book technology altogether. J.K Rowling has thus far refused to make any of her Harry Potter books available digitally because of piracy fears and a desire to see readers experience her books in print.

And yet, as any one with a minute to spend on bittorrent might be able to tell you, it’s not hard to find scans of any Harry Potter book. And yet, Rowling has sold gazillions of dead tree books.

Ultimately, the headline of this article is totally misleading. For all the wailing and gnashing of teeth over piracy, those who buy e-books buy more real books. Those who download music buy more music. For every negative consequence of new technology, there is a positive opportunity. Some people will realize this and benefit from this new technology, creating new markets and products. Others will try to cling to business practices which they are comfortable with, and will fight a losing battle against the new technology by annoying their customers with new annoyances to “protect” their works.

Well, I got a new gadget in the mail today: an SDR-IQ from rfspace.com. It’s a cute little gadget: a general purpose receiver that can deliver the quadrature signals for any 192Khz of the spectrum anywhere from 100Hz (yes, Hz) to 30Mhz. It is a small black box, with only three connectors: a USB, a regular serial port (used for rig control) and a BNC port for attaching an antenna. I fired it up, and right away started to find interesting things: for instance, here is the frequencies around 5.8Mhz:

If you look carefully, you can see that this is actually an AM signal. The carrier and a couple of sidebands are visible to each side of the received signal. If you click on the signal, and select the AM demodulator, you get the following audio:

AM modulated Morse code at 5.8Mhz, recorded around 06:30, Jan 5, 2010

A quick google of the web indicates that this is a Cuban numbers station. Pretty nifty, and probably never would have discovered it without using the RFSPACE SDR-IQ.

You’ll be hearing more about this gadget in the future.

Addendum: I’m not the only person (obviously) to hear these guys.

Over on NT7S’s Ripples in the Ether blog, he presents a link to a project by Joachim, DL1GSJ, a very nifty little SDR designed to operate near the 30m QRSS watering hole frequncy. It uses pair of subharmonic mixers, whose operation I admit I don’t completely understand, but I’m bookmarking the circuit for later consumption.

de draaggolf     ~~~~~: 30m Subharmonic I/Q-SDR Receiver.

While scanning QRP-L today, I found an interesting link to a project which gave some details about a little WWV receiver that can serve as a frequency standard.   I haven’t had the time to work out how it all works, but it looks reasonably straightforward:

Here’s the original schematic from Chuck Adams, K7QO:

Nick, WA5BDU has some variations and additional comments which are interesting:

autodynereceiver kennnick.

I hadn’t worked SAUDISAT 1C (aka Saudi Oscar 50, or SO-50) in quite some time. My recollection was that it was a trickier satellite to work than AO-51, and this pass proved that my recollections were correct. I had significant problems with deep fades. Still, I managed to exchange calls with WD9EWK, K0KU, and N7EDK. Here’s the recording.

(I was working this with my TH-D7A HT and my Arrow Antenna).

2010-01-03-SO-50-FM, recording of WD9EWK, K0KU and N7EDK

I was driving around a bit yesterday (I needed a new hand nibbling tool to punch some holes in a project box, and wanted to get out of the house anyway, so a jaunt over to Harbor Freight seemed like a good way to kill two birds with one stone) so I did what I normally do: I downloaded a couple of amateur radio podcasts, and fired them up on my car stereo.

One of the podcasts I listen to is the Amateur Radio Newsline, and they were running a story entitled RESTRUCTURING: WIRELESS BROADBAND WANTS MORE SPECTRUM FROM ANYONE. The basic gist (go ahead and listen to the podcast if you like more information) is that Rick Boucher (D) is asking that the federal government undertake a complete inventory of radio spectrum for the purpose of determining reallocations to satisfy the growing need for additional wireless data services. In addressing the possible threats to the amateur service:

Its when you get to 200 MHz and above that the hunt will likely be focused and right there lies the relatively silent 222 to 225 MHz allocation. Above that is the 70 centimeter ham radio allocation which is secondary to the Federal Government. If the government were to decide to move completely out of 70 centimeters it could put a lot of weak signal operators and repeaters in a fight to keep the spectrum on which they now reside.

But likely the real losses would be up in the microwave range where hams hold a lot of spectrum that to date is used mainly by experimenters. And a lot of it sits adjacent to bands used by other services that might eventually be pushed by government decree into moving elsewhere or simply told to disband to make way for more wireless broadband services.

For amateur radio as an FCC licensed communications service this means being vigilant about attempts at reallocations that might include any bands that we use. It also means making certain that our ham radio political leaders are aware that every hertz from DC to light will be under scrutiny by both the wireless broadband industry and the government in the coming months and years.

So, here was my thought: that amateur radio use at UHF+ is actually on very thin ice. The reality of amateur radio at UHF and above is that it’s an incredibly fringe activity. I just used K5EHX’s repeater search engine to find all repeaters which provide coverage to my QTH. There are 85, but only two are not in the 2m or 70cm band. One is on 6m, the other is on 1285 Mhz. While this isn’t the whole story with respect to microwave operation, I think it is indicative of the kind of numbers were are talking about. Probably only one percent of ham radio takes place on the bands above 70cm, and that is probably being rather generous.

When we say that our “ham radio political leaders” should remain vigilant against possible spectrum reallocation, I think that we are shifting the responsibility (and in the future, likely the blame) to them, when the responsibility really lies with us. We as radio amateurs are simply not doing enough to justify our use of UHF+ spectrum. When we rely on political action committees to justify our use of this valuable public resource, we should be working hard to provide them with every possible justification that they can use. It isn’t Congress who is placing these frequencies in peril: it is our own inactivity which does so. If we lose 1.2GHz, or 220Mhz, or any of our other allocations, it will be because we frankly aren’t using them enough. If I thought that these frequencies could be effectively used to give Internet broadband to millions of underserved Americans, I’d have to say “take those frequencies, we will miss them, but we had our chance with them”.

What do you all think?

More fun on HO-68!

During a low elevation pass, Mike DK3WN and Henk, PA3GUO made the very first SSTV contact via HO68 – linear transponder. Images were transmitted between the two radio stations in Germany and The Netherlands. Signals were transmitted to HO-68, which was 1200km above earth and about 8000km distant from the radio amateur stations.

Check out the pictures!

via DK3WN SatBlog » XW-1 SSTV.

I keep thinking that I should build one of these, but have never gotten around to it. Bookmarking this interesting link for future reference:

Build Your Own 3D Scanner: Optical Triangulation for Beginners.

I don’t really have the hardware to effectively transmit to satellites in linear transponder mode. To really make it straightforward, you probably would like to have a computer to handle the Doppler tracking and antenna pointing, and a full duplex SSB transmitter (or a pair of ordinary ones). That’s more than I am willing to invest at the moment, but with my little FT-817, you can actually receive these birds pretty easily, using my ever present Arrow antenna and just tuning by hand. So, that’s what I did this morning: here is my recording of HO-68. It begins with a bit of the CW beacon, then shows me tuning around to try to find SSB signals. Sometimes, the tracking is pretty good, but later in the recording, my next door neighbor began mowing his lawn and running a leaf blower, and it was hard to hear (I need to use my over the ear headphones instead of these earbuds I’ve used for FM passes). Anyway, here’s the recording:

2009-12-30-HO68-SSB, recording by K6HX in CM87 using an FT-817 and hand tuning