Monthly Archives: January 2010

KnightsQRSS blog

Joachim, PA1GSJ has decided to put up a blog for the KnightsQRSS. I recommend all those interested in QRSS operations to go ahead and subscribe, then we’ll have a common place to talk besides the mailing list.

That reminds me, I really do need to get my own site, QRSS.info working again.

KnightsQRSS.

Perils and Pitfalls of SDR | Signal and Noise

Jeff (KE9V) posted an interesting commentary on an article by G4ILO about why he’s not excited by software-defined radio. My comments are mostly directed to G4ILO’s original statements.

Before I begin the rant proper though, let me say that if something in ham radio doesn’t appeal to you, you should by no means think that I’m asking you to change your feelings. Everyone is free to explore and experience their hobbies in a way that maximize their own personal enjoyment, without any kind of justification or rationalization required.

But somethings I thought that G4ILO were just a little off target, and as someone who is excited by software-defined radio, I think its good that I air the counterview.

G4ILO begins with:

I say this even though I am a programmer of sorts. I have tried to learn how SDR works with the idea that if I could write my own SDR software it might become an aspect of the hobby I could get interested in. But I can’t. The math is totally beyond me and I just can’t understand how it works at all. The majority of radio amateurs without any knowledge of programming don’t have a chance. Which makes the limit of most people’s technical challenge in an SDR future that of getting somebody else’s SDR software to work. And after a lifetime working with computers frankly I don’t find faffing about with PCs very much fun.

In some sense of course, this is entirely correct. If we compare the number of users of PSK31 to the number of people who understand the modulation technique in sufficient detail to write their own working implementation, I’d say the ratio is likely 1000:1 or 10000:1. But I think it is odd to say that someone “doesn’t have a chance” at understanding software defined radio. I’ve managed to work it out. Most software defined radios are just big down converters, using the principles of phasing that are well exposed in the ARRL handbooks and in books like Experimental Methods in Radio Frequency Design. Once you understand how the digital down conversion works, you can work on designing good low pass filters. Again, the math is a bit heavy, but it isn’t completely impenetrable. Once you have those two bits, making a SDR that receives CW and SSB signals isn’t particularly difficult. The overwhelming majority of hams won’t ever do that, but so what? Isn’t it great that we are able to do so?

G4ILO continues:

A basic understanding of electronics is one of the prerequisites of getting a ham radio license. Although most of us could not design an Elecraft K3 and many of us choose never to design or even build any part of our station, most of us can understand how radio circuits work and quite a few of us can build simple circuits from a schematic. Some of us can even design circuits from scratch – a lot more of us I’d wager than could write their own SDR software.

Again, this may be true, but I also suspect that it is because there isn’t nearly the overlap between ham radio operators and experienced software engineers. The ham radio population as a whole isn’t actually all that computer saavy: there are exceptions naturally, but in general most software written by hams is pretty crufty. Designing feedback amplifiers and impedance matching networks isn’t particularly easier than writing software defined radio software: it’s just different. Everything is hard when you don’t know how it works.

I also expect that while most hams think they understand how lots of things in their radio work, the number who actually do and are able to design bits of their own radio gear effectively is quite low. Guys like SolderSmoke’s Bill Meara who’ve been hams for 20 years are still working to really understand mixers and amplifiers, and benefit greatly from luminaries like Wes, W7ZOI and Rick, KK7B.

The reason I don’t like SDR is that it reduces the majority of us to the role of appliance operators. That may be fine for those who are happy being appliance operators and just want the best technical solution for working weak DX or amassing the most contest points. But for the tinkerers and builders SDR doesn’t leave a lot to experiment with, because most of the interesting stuff happens in software, inside the computer, where we don’t have the tools or the knowledge to tinker with it. If you are using a SoftRock or a top of the line Flex you will be looking at the same software user interface. And I don’t find that a very enthralling prospect.

The majority of amateur radios are already appliance operators. That trend is at least 40 years old, and it shows no sign of slowing. Most of the gear that you can buy now already has a large software component, hidden deep inside the unit where it is not only difficult but literally impossible for you to examine it. The glory of things like the Softrock is that even if you have a modest understanding of electronics, you can figure out what how it works, and can use your ordinary every day PC to process the signals from it. If you only use Rocky, well, then you’ve built a $15 receiver that can do AM, FM, SSB and CW with varying filters. If you examine the circuit, you”ll learn how Tayloe detectors work, and why they are a good idea. If you spend a bit more of time, you might begin to understand how sampling works, what the Nyquist limit is about, and how you can construct good heterodyne filters in software.

And frankly, the idea that software defined radios don’t leave much room for experimentation makes me blow milk out my nose. If it isn’t the kind of experimentation that you are personally interested in, so be it, but there is lots to do. I’ve been working on my own code for detecting QRSS beacon activity. I’ve got a perverse interest in modes like Hellschrieber, and thought that making a compact, self-contained rig to do Hellschrieber would be a fun thing to do, and could be powered by something as cheap and inexpensive as a dsPIC. Even if you just like RTTY, you could probably make a small self-contained rig that could decode multiple RTTY signals simultaneously. Or, you can develop (or someone can) really nice PC interfaces, like the one from sdr-radio.com. I’d like to see a SDR kit or design that includes the analog capture as well (we should stop relying on sound cards, which have characteristics which aren’t always in tune with our needs) so we can sever the ties with our laptops. I’d like to see software defined radios with wide bandwidth available at VHF+ (but perhaps cheaper than the ones available from ettus.com).

Software defined radios aren’t a panacea. They don’t solve all possible problems, or even any given problem in the best possible way. They do however give hams a set of tools and techniques that are versatile and exciting, and I welcome their addition to ham radio.

W3EEE on LF radio..

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.

Jonathan Ward – MIT – Machines That Make

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.

Gilbert Cells

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.

Digital Radio Mondiale, recorded on the SDR-IQ, decoded with GNU Dream

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:

2010-01-07_1919_001

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.

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

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.

New gadget in the shack: an RFSPACE SDR-IQ

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:

2010-01-04_2222-cuban-numbers

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.


httpv://www.youtube.com/watch?v=P_YxgDt8aM0

30m Subharmonic I/Q-SDR Receiver

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.

Autodyne receiver for WWV

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:

Picture 1

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

autodynereceiver kennnick.